Shifting Lands - New insights into periglacial geomorphology

European Science Foundation (ESF) Network SEDIFLUX Sedimentary Source-to-Sink-Fluxes in Cold Environments

Second Workshop SHIFTING LANDS. NEW INSIGHTS INTO PERIGLACIAL GEOMORPHOLOGY Clermont-Ferrand, France 20 – 22 January, 2005 followed by

6e Journée des Jeunes Géomorphologues Program and abstracts edited by

Samuel ETIENNE University of Clermont-Ferrand

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Shifting Lands. New insights into periglacial geomorphology

Scientific partners European Science Foundation / Fondation Européenne pour la Science (ESF) International Geographic Union / Union Géographique Internationale (IGU) International Permafrost Association (IPA) International Association of Geomorphologists (IAG) Centre National de la Recherche Scientifique (CNRS) Comité National Français de Géographie (CNFG) Groupe Français de Géomorphologie (GFG)

Local organizer Université Blaise-Pascal Clermont-Ferrand II GEOLAB - CNRS UMR 6042 Géodynamique des milieux naturels et anthropisés, Clermont-Ferrand

S. Etienne (ed.), 2005. Shifting lands. New insights into periglacial geomorphology.

ESF-Sediflux Network, second conference, Clermont-Ferrand 20-22 January 2005. Coll.

Géoenvironnement, Séteun, ClermontFerrand, 122 p.

Published by : Editions Séteun 3 place du changil 63000 Clermont-Ferrand www.seteun.net Collection Géoenvironnement, volume 2 ISBN : 2-913169-10Dépôt légal : 1er trimestre 2005

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Program and abstracts

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Shifting Lands. New insights into periglacial geomorphology

Thursday 20th January

Program

8h-9h

Registration and welcoming of participants

9h-9h30

Special guest paper #1 Colin E. Thorn – Context, focus, methodology, and philosophy in periglacial geomorphology.

9h30

Paraglacial dynamics Session

9h30-10h

Special guest paper #2 Colin K. Ballantyne – Paraglacial landscapes dynamics

10h-10h15

Coffee break

10h15-11h30 Oral papers • Lasafam Iturrizaga – Paraglacial (transglacial) landscapes in the Karakorum Mountains.

• Etienne Cossart, D. Bourlès, R. Braucher, M. Fort – The importance of rock-slope failure in the high-alpine paraglacial systems. Examples from Upper-Durance area (Southern Alps of France).

• Vincent Jomelli, Daniel Brunstein, D. Grancher, Pierre Pech, M. Deque, L. Terray – Impacts of climatic change on debris flows dynamics in the French Alps (Massif des Ecrins): recent and prospective analysis.

• Myrtille Moreau, Denis Mercier, Dominique Laffly, Erwan Roussel – Runoff impact on plant colonization on the forefield of midre Lovénbreen, Spitsbergen (79°N) since the end of the Little Ice Age. • Monique Fort – How significant is the distinction between paraglacial and seismotectonically induced mass-movements in active orogens? insights from the Pamir-KarakorumHimalayan ranges.

11h30– 12h30 14h 14h-14h30

ESF-SEDIFLUX Working groups # 1 Weathering Session Special guest paper #3 Kevin Hall – Perceptions of rock weathering: some thoughts on attributes of scale.

14h30-17h Oral papers • Cécile Tsao – Blockfields of Gaspé peninsula: origine and age.

• Marie-Françoise André, Kevin Hall, Joselito Arocena – Stone runs in the Falkland Islands : periglacial or tropical ?

• Matti Seppälä, Sean Campbell, Robert G. Darmody, Colin E. Thorn –Chemical and biological weathering of granitic tors in Arctic Finland.

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

• • • • • •

Dominique Sellier – L’influence respective des processus périglaciaires et des processus glaciaires dans l’élaboration des felsenmeers de montagnes de l’Europe du Nord-Ouest.

Dawn T. Nicholson, Frank H. Nicholson – Post-glacial weathering form and process in a periglacial environment, Hardanger Plateau, southern Norway Kenji Yoshikawa – Weathering of Granite around the summit of Denali (Mt. McKinley), Alaska, USA. Achim A. Beylich – Sedimentary source-to-sink-fluxes in arctic-oceanic swedish Lapland – results from process geomorphological investigations at the landscape level.

Christine Elliott – Influence of moisture in rock weathering in cold climates.

Jan Boelhouwers – Rock weathering by thermal stress: observations from the antarctic and critical discussion.

17h30-18h

Plenary oral presentation of Paraglacial and Weathering posters

Paraglacial dynamics • Volker Rachold & the ACD Group – Arctic Coastal Dynamics (ACD): overview of an International Research Program.

• Denis Mercier, Marie-Françoise André, Samuel Étienne, Dominique Laffly, Myrtille Moreau, Dominique Sellier, Joëlle Dupont, Angélique Prick, Grzegorz Rachlewicz – Paraglacial dynamics in Spitsbergen. Pr. 400 – Geomorphoclim – French Polar Institute Paul-Émile Victor.

• Jasper Knight – Formation and deformation of periglacial deposits, Cornwall, SW England.

• Bernd Etzelmuller – The influence of permafrost on paraglacial processes.

• N. Casarosa, P.R. Federici, M. Pappalardo, A. Ribolini – Paraglacial fans in the Maritime Alps (Western Alps, Italy): landforms, sediments and significance.

• Knut Stalsberg, E. Larsen – Results and challenges in studying past and current valley-to-fjord sediment transport - The SEDITRANS example from western Norway.

• Samuel Etienne, Virginie Comte, Morgane Priet-Mahéo, Erwan Roussel – Presentation of the GEOMORPHOGLIS program (Postglacial geomorphic dynamics in south-Iceland, 2006-2009).

Weathering • Achim A. Beylich, Karl-Heinz Schmidt – Water chemistry and solute fluxes in the Kidesjoki catchment, subarctic Finnish Lapland.

• Robert G. Darmody, Charles E. Allen, Colin E. Thorn – Soil and weathering on a glacial foreland, Storbreen, Jotunheimen, Norway.

18h-18h45 20h

Poster session : Paraglacial and Weathering Buffet auvergnat 7

Shifting Lands. New insights into periglacial geomorphology

Friday 21st January Periglacial and permafrost dynamics Session 9h-9h30

Special guest paper #4 Hugh French – Periglacial geomorphology as a branch of geocryology.

9h30-10h15 • • •

Session Periglacial and permafrost dynamics Subsession : Permafrost dynamics Xavier Bodin – Investigations on permafrost in the French Alps: first results and future orientations.

Julia Boike, Kurt Roth, Olaf Ippisch, Birgit Hagedorn – Mud boils and solute fluxes in periglacial landscapes.

Guido Grosse, L. Schirrmeister, H.-W. Hubberten, Ch. Siegert, V.V. Kunitsky – Remote sensing and classification of thermokarst structures formed during Holocene climate changes in the Laptev Sea coastal region, NE Arctic Siberia.

10h15-10h45 Coffee break 10h45-12h Periglacial dynamics Subsession I • Martin Gude – Periglacial geosystem change: event versus trend dynamics.

• Kellerer-Pirklbauer Andreas, Avian Michael, Lieb Gerhard Karl, Proske Herwig – The influence of geological conditions on the distribution of rock glaciers - Niedere Tauern Mountain Range, Styria, Austria.

• Enrique Serrano, Carlos Agudo – Morphogenetic phases of rock glacier in the high mountain of Aragonese Pyrenees.

• Christophe Lambiel – Ground surface temperature in scree slopes of high altitude : case studies in the Valais Alps.

• J.J. González-Trueba, E. Serrano – Periglacial morphodynamic and environment in the central massif of Picos de Europa, Cantabrian Range, north Spain.

12h-13h45

Lunch

13h45-15h Periglacial dynamics Subsession II • Marianne Font, J.-L. Lagarde, D. Amorese, J.-P. Coutard, J.-C. Ozouf, G. Guillemet – Laboratory simulation of scarp degradation under freeze/thaw cycles.

• V. Golosov, Nadezda Ivanova – The role of hollow systems in the modern sediment balance of cultivated watersheds (the forest-steppe zone of central Russia).

• Vladimir Belyaev – Relics of periglacial processes in modern relief, soil cover and surface geology of Central russian plain.

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

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Piotr Migoñ, Andrzej Traczyk – Rocks, glacial history and periglacial landscapes of the Sudetes, Central Europe.

H. Lantuit, W.H. Pollard – The relation between retrogressive thaw slumps polycyclic pattern and shoreline evolution on Herschel Island, Yukon Territory.

15h-15h30

Coffee break

15h30-16h10 Plenary oral presentation of Permafrost and periglacial dynamics posters • Avian Michael, Kellerer-Pirklbauer Andreas – The relationship between kinematics and geomorphology of an active rockglacier, Hinteres Langtalkar, Hohe Tauern, Austria.

• Sébastien Monnier – Mapping of an unusual ice-cored rockglacier, in the Mont Thabor area (northern French Alps), linked to the deglaciation since the Little Ice Age. • V.V. Kunitsky, L. Schirrmeister, H. Meyer, G. Grosse – Small scale initial thermokarst in the region of Cape Mammoth Tusk (northern middle Siberia).

• Armelle Decaulne, Þorsteinn Sæmundsson – Slush flows in north-western Iceland and their geomorphological impact. The case study of Bíldudalur.

• Thomas Glade, Rainer Bell – Sediment budget assessments as a prerequisite for landslide hazard analysis - examples from arctic environments in Iceland.

• Hanna Ridefelt – Spatial modelling of solifluction processes in the Abisko area, northern Sweden.

• Maciej Dabski – Sorted patterned grounds in marginal zones of Fláajökull (SE Iceland) and Elisbreen (NW Spitsbergen).

• Reynald Delaloye – Shall we reconsider the processes controlling the spatial distribution and the evolution of permafrost in an alpine environment ?

• Nicola Casarosa & the AIGeo Working Group – The study of relict forms for the reconstruction of past periglacial environments in the Italian mountain chains.

• Enrique Serrano, Carlos Agudo – Morphogenetic phases of rock glacier in the high mountain of Aragonese Pyrenees.

• J.J. González-Trueba, E. Serrano – Periglacial morphodynamic and environment in the central massif of Picos de Europa, Cantabrian Range, north Spain.

• Georg Schwamborn, Lutz Schirrmeister, Christine Siegert, Hanno Meyer, Hans.W. Hubberten, Grigory Fedorov – Late Quaternary terrestrial records for a permafrost site nera the impact crater ake El’Gygytgyn, Chukotka, NE Siberia 16h10-17h

Permafrost and periglacial dynamics posters

17h-17h30

Special guest paper #5 John C. Dixon – Scale in Periglacial Geomorphology.

20h

Gastronomic dinner 9

Shifting Lands. New insights into periglacial geomorphology

Saturday 22nd January 9h-10h30 • • • • • •

Periglacial dynamics Session III Nival and snow-related processes Subsession

Lutz Schirrmeister, G. Grosse, V.V. Kunitsky, A.J. Dereviagin – The role of nival processes for modern and Pleistocene landscape genesis in Northeast Siberia.

M. Valcárcel-Díaz, P. Carrera-Gómez, A. Pérez-Alberti – Nival bedrock erosion at a seasonal snow patch site from the Cuiña cirque, Ancares Sierra, northwestern Spain.

Thomas Glade, Kirsten von Elverfeldt – MultiRISK - modelling natural risks and its application under aspects of global warming and land-use changes in northwest Iceland.

Tobias Heckmann, Michael Becht – Quantifying and modelling the contribution of full-depth snow avalanches to the sediment budget of high-mountain areas based on field measurements and spatial modelling. Þorsteinn Sæmundsson, Armelle Decaulne – Morphological impact of ground snow avalanches in Iceland.

Robert G. Björk, Ulf Molau – Snow distribution and biocomplexity in alpine landscapes: a progress report.

10h30-11h

Coffee break

11h-12h

ESF Working groups meeting #2

12h

Conclusions of the ESF-Shifting lands Conference

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Sixième Journée des Jeunes Géomorphologues Groupe français de Géomorphologie 14h-18h30 •

• • • • • • • • •

• •

Etienne COSSART – Estimation des bilans de masse glaciaire par intégration d’héritages géomorphologiques dans des Modèles Numériques de Terrain : application à trois glaciers du Massif des Ecrins.

Morgane LE DARZ – Dynamique glaciaire et paléogéographie pléistocène dans le massif de la Chartreuse (Alpes du Nord, France).

François AMELOT – Mise en évidence géomorphologique des modalités de l’instabilité chronique du versant occidental du Mont Margériaz (Savoie, France).

Sylvain JOBARD – Les modalités du retrait glaciaire dans le bassin versant du Haut Arc depuis la fin du Petit Age Glaciaire aux années 2000 (Savoie, France).

Florence GARLATTI – Intégration de la diversité torrentielle dans l’évaluation du risque torrentiel - cas du bassin de l’Arzino (Friuli, Italie du Nord-Est).

Gilles GARITTE – Contribution à la gestion du risque torrentiel en vallée de la Clarée (Hautes-Alpes, France) Emmanuel RIBES – Dynamiques morpho-sédimentaires actuelles d’une rivière fortement aménagée : le cas de la basse Durance.

Caroline RUFIN – Les morphologies sous-marines, témoins des variations eustatiques depuis le Pléistocène, dans les atolls de l’archipel des Maldives.

Guillaume MARIE – Evolution du couple falaise-plate-forme d’érosion marine sur les littoraux volcaniques de l’archipel d’Hawaï.

Isabelle SICHE – Evolution historique et reconstitution de la dynamique d’un paléofleuve sur une plaine côtière subsidente. Exemple de la “Natiso” sur le site du port fluvial d’Aquilée (Vénétie Julienne, Italie du Nord).

Stéphane CORDIER – L’évolution des vallées de la Meurthe et de la Moselle dans le Bassin parisien et le Massif schisteux rhénan depuis le Pléistocène moyen : premiers résultats.

Matthieu GHILARDI – Dynamiques géomorphologiques et évolution Holocène de la plaine de Thessalonique - étude géoarchéologique.

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Shifting Lands. New insights into periglacial geomorphology

Special Paper #1

CONTEXT, FOCUS, METHODOLOGY, AND PHILOSOPHY IN PERIGLACIAL GEOMORPHOLOGY Colin E Thorn Department of Geography University of Illinois 220 Davenport Hall 607 South Mathews Ave. Urbana, IL 61801 U.S.A.

Science is a balance between specialization and generalization. Of necessity individual scientists specialize, while small groups of scientists generalize to some degree by creating subdisciplines, such as periglacial geomorphology.

Nevertheless, the best science is always measured by the breadth of its applicability. In periglacial geomorphology, as in all subdisciplines, practitioners need to identify both the peculiar and general attributes of their field. Consequently, the validity of a subdiscipline is established by both a focus and a context. A strong discipline is characterized by balance between theory and practice, accepted knowledge and skepticism, and past and future trajectories.

Much of this perspective is captured in the two colloquial adages ‘How can we know where we are headed if we do not know where we have been?’ and ‘Necessity is the mother of invention’. In large disciplines the sheer number of practitioners fosters diversity and 12

tends to drive the discipline forward: in a small discipline, such as periglacial geomorphology, pressure on the established disciplinary framework (paradigm for relativists) tends to be slight and a conscious effort to challenge it is often needed. In the absence of challenge, accepted practice tends to linger too long and disciplinary progress is slowed. I will attempt to survey some individual concepts stemming from the issues outlined above. For example, what does periglacial geomorphology add to general geomorphology? Is the focus of cold region and periglacial geomorphology the same? What is the relationship between geocryology and periglacial geomorphology?

What are the primary inputs to, and constraints on, a periglacial landscape?

What is the spatial and temporal diversity of periglacial regimes? At best the exercise can only be one geomorphologists’s view of his subdiscipline, at worst it may simply be selfevident and trivial. Nevertheless, the exercise

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

is an essential one that needs to be performed individually and collectively, and with some frequency. This is not because we should have the illusion that some authorized or correct way to undertake periglacial geomorphology will emerge, but rather that an overt, critical

perspective on our subdiscipline will steer our research in an optimal manner. Furthermore, it is an essential exercise because we may rest assured that such an approach is the prevailing one in both large and successful scientific disciplines.

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Shifting Lands. New insights into periglacial geomorphology

Special Paper #2

PARAGLACIAL LANDSCAPE DYNAMICS Colin K. Ballantyne School of Geography and Geosciences University of St Andrews Fife KY16 9AL Scotland

The retreat of glacier ice frequently exposes landscapes that are in an unstable or metastable state, and consequently liable to erosion and sediment release at rates greatly exceeding background denudation rates. Such glacially-conditioned landscape modification is decribed as paraglacial. The unifying rudiment of all forms of paraglacial response is that of glacially-conditioned sediment availability, implying that rate of sediment reworking can be approximated by the exhaustion model: St = Sa e –lt

(1)

Where t is time elapsed since deglaciation, St is the proportion of ‘available’ sediment remaining at time t, Sa is total ‘available’ sediment at t = 0 and l is the rate of loss of ‘available’ sediment. Relaxation of landscape elements to nonglacial conditions operates over timescales of 101 to >104 years, and is conditioned by both the nature of operative processes and spatial scale. In the case of 14

primary reworking of glacigenic sediment extrinsic perturbation may rejuvenate sediment flux long after termination of the initial period of paraglacial adjustment.

Landscape-scale (primarily fluvial and coastal) systems also exhibit intrinsically complex responses due to reworking of secondary paraglacial sediment stores.

Paraglacial landform succession reflects the fact that different paraglacial subsystems relax over different timescales, so that some paraglacial sediment stores experience net erosion even as others continue to accumulate. Over millennial timescales individual sediment stores (such as talus, debris cones, alluvial fans and valley fills) exhibit net sediment accumulation then net sediment loss. A general steady-state model of paraglacial sediment storage is developed based on the equation: S = (Sa – Sa e-lt) e-kt

(2)

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

where S is storage volume at time t, and k is the rate of sediment loss from the sediment store. Sediment budgets for any time t can be retrodicted or predicted through derivation of Sa, l and k provided that two points on the curve described by the above equation are known: (t’, Sm) and (t’’, Sv), where t’ is time since deglaciation when the sediment store reaches its maximum volume, Sm is the maximum volume of stored sediment, t’’ is time elapsed since deglaciation and Sv is the present volume of stored sediment.

These models have important implications for the nature of landform development and rates of mass transport in formerly-

glaciated environments. Because paraglacial sediment sources are nonrenewable, they imply that eventual change from net sediment accumulation to net sediment loss is an intrinsic characteristic of all paraglacial sediment stores unless sediment loss is negligible, and need not reflect changing boundary conditions. Equally, measured rates of mass transport are likely to be conditioned by time elapsed since deglaciation, and cannot be considered representative of the full span of post-deglaciation time. The influence of paraglacial inheritance on mass transport rate is considered for talus accumulation and the development of talus rock glaciers.

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Shifting Lands. New insights into periglacial geomorphology

Special Paper #3

PERCEPTIONS OF ROCK WEATHERING: SOME THOUGHTS ON ATTRIBUTES OF SCALE Kevin Hall Geography Program University of Northern British Columbia 3333 University Way Prince George BC Canada V2N 4Z9

Simplistically, breakdown of rock in cold environments is frequently viewed as a singularity in the sense that no temporal or spatial scale attribute is ascribed to the notion of weathering (i.e. ‘rocks in cold regions are shattered by frost action’). Alternatively, weathering is considered to fall into one of two categories - ‘macrogelivation’ or ‘microgelivation’: the former being with respect to ‘frost wedging’ of large blocks or bedrock and the latter to granular disintegration or flaking. In the same manner, rarely are transducer type and data frequency considered in respect to the scale of the weathering under investigation. The data themselves are also often non-existent or of a spatial scale inappropriate to the issue under review: i.e. the absence of rock temperature at depth for consideration of stresses created by thermal gradients to produce flaking.

In much the same way, temporal issues are 16

frequently ignored: the process operative now may be far removed from those which initiated breakdown of that rock. Equally, in cold regions, the transition of process through the annual cycle and the synergy that devolves from this is often lost in the pre-occupation with the role of cold and hence the need for winter data at the expense of measuring parameters appropriate to the summer. Here data from Antarctica, Canada and Tibet will be used as a medium for showing the highly complex and inter-acting attributes of scale of monitoring (grain vs rock blocks), temporal scales of data acquisition (seconds to days), spatial attributes in terms of aspect and depth, the impact (or not!) of albedo, and how these data determine our perceptions of the weathering regime. It will be shown that many of our traditional notions of weathering in cold regions (and other environments) have been highly skewed by the scale attributes of

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

our data and that as these scale attributes of data collection are improved so many of our long-cherished perceptions and paradigms are brought into question. With more and better data so it may require a reappraisal of

the weathering basis and climatic implications of many primary landscape-level periglacial concepts (e.g. nivation, cryoplanation, blockfields, tors, etc).

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Shifting Lands. New insights into periglacial geomorphology

Special Paper #4

PERIGLACIAL GEOMORPHOLOGY AS A BRANCH OF GEOCRYOLOGY Hugh French Professor Emeritus Departments of Geography and Earth Sciences University of Ottawa Ottawa, Ontario K1N 6N5 Canada E-mail: hughfrench@rogers.com

This paper summarises the central role that permafrost plays in fashioning the periglacial landscape.

First, the nature and diversity of periglacial landscapes are briefly described. Second, it is argued that the process underpinnings of traditional Pleistocene-oriented periglacial geomorphology were formulated prior to obtaining all the necessary observational and theoretical data concerning the nature of the processes that fashion the periglacial landscape. Third, it appears that much modern periglacial research has become increasingly concerned with permafrost and permafrostrelated processes and landforms. Today, periglacial geomorphology is considered by some to be a branch of geocryology It is concluded that periglacial geomorphology must explicitly position itself as a bridging discipline between geocryology, geomorphology and Quaternary science. Permafrost-related process studies will link the discipline to geocryology. Studies 18

involving cryostratigraphy and cryolithology will permit inferences to be made about Pleistocene paleo-periglacial conditions. The continued study of frost action, cold-climate (cryogenic) weathering, and the azonal processes associated with wind, wave action, running water, and snow, all of which assume distinct characteristics in cold non-glacial regions, will link periglacial geomorphology to mainstream geomorphology.

Key words: periglacial geomorphology, permafrost, geocryology, Quaternary science.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Special Paper #5

SCALE IN PERIGLACIAL GEOMORPHOLOGY John C. Dixon Department of Geosciences University of Arkansas Fayetteville AR 72701 U.S.A.

Scale is a fundamental theoretical issue in geomorphology, and while it has received considerable attention from process geomorphologists as a group, it appears to have received disproportionately less attention from periglacial geomorphologists.

The focus of this paper will be on scale dependence and linkage within soil and weathering systems and hillslope evolution.

Examples will be primarily drawn from the Colorado Rocky Mountains and Swedish Lapland. While issues of temporal and spatial scale are inextricably linked, the focus of this presentation is on spatial scale issues and particularly on issues of upscaling in the context of periglacial landform and landscape evolution. In considering scale issues in periglacial geomorphology, it is important to keep in mind that scale issues affect three fundamental components of the Earth Surface System: form, process, and process controls.

It has been widely argued that landforms, landscapes, and geomorphic processes are

scale dependent. According to Phillips (1999), that means that consistent representations of form and process across the Earths surface cannot be meaningfully extended from representations at any given scale. Haff (1996) has argued that the appearance of emergent variables at large scales which are not identifiable at smaller scales preclude upscaling as a way of understanding large scale systems. At best, it has been argued that inferences can be extrapolated no more than one or two orders of magnitude. Yet great effort has been expended by geomorphologists to investigate the idea of scale linkage and how a greater understanding of landscape and landform evolution might be obtained by being able to upscale or downscale.

Thorn (1988)has suggested three means by which the problem of extending research findings undertaken at one scale might be transferred to another scale. These include the use of methodologies that specifically exclude scale variability such as the use of dimesionless values, a second approach is to 19

Shifting Lands. New insights into periglacial geomorphology

smooth small scale data so that larger scale patterns begin to emerge using techniques such as trend surface analysis, and thirdly the reformulation of small scale data using some sort of synthetic approach (eg. Caine, 1979) to understanding landforms by aggregating smaller scale data derived at essentially the plot level. Church (1996) however argues that in reality, there is presently no coherent theoretical framework which meaningfully links geomorphological processes operating at restricted spatial and temporal scales to the evolution of landscapes. He suggests that perhaps the most appropriate solution to the lack of sound theoretical frameworks is the aggregation (averaging) of event (process) patterns to understand landscape evolution.

While processes and forms may be scale dependent, controlling factors (driving forces) may be largely scale independent. That is to say controlling factors (geology, hydrology, climatology, biogeography) may influence when and where processes operate and forms evolve, but not how they operate. A holistic understanding of periglacial landform and landscape evolution that largely transcends or circumvents scale dependence and linkage problems may be achieved by adopting such a factorial approach to landscape evolution (Phillips, 1999). Another potentially fruitful solution to the dilemma is to apply/adopt research methodologies that are most appropriate for a given scale of inquiry. These

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methodologies might include, but are not limited to, electron microscopy at the smallest scales, field and laboratory instrumentation at intermediate scales and digital modeling at the largest scales (Viles, 2001; Thorn, 2003).

References Caine, N. 1979. The problem of spatial scale in the study of contemporary geomorphic activity on mountain slopes (with special reference to the San Juan Mountains). Stud. Geomorphol.

Carpatho-Balcanica. 13, 5-22.

Church, M. 1996. Space, time, and the mountain.

How do we order what we see? In: Rhodes. B.L. and Thorn, C.E. (eds.). The Scientific Nature of Geomorphology. John Wiley and Sons.

Chichester. pp 147-170.

Haff, P.K. 1996.

Limitations on predictive modeling in geomorphology. In: Rhodes, B.L. and Thorn, C.E. (eds.). The Scientific Nature of Geomorphology John Wiley and Sons. pp337-358.

Phillips, J.D. 1999. Methodology, scale, and the field of dreams. Annals of the Association of American Geographers, 89, 754-760.

Thorn, C.E. 1988. Introduction to Theoretical Geomorphology. Unwin Hyman, London, 247p.

Thorn, C.E. 2003. Making the most of new instrumentation. Permafrost and Periglacial Processes, 14, 441-419 Viles, H. 2001. Scale issues in weathering studies.

Geomorphology, 41, 63-72.

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Abstracts (by order of appearance)

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Shifting Lands. New insights into periglacial geomorphology

Paraglacial Session Oral Paper

PARAGLACIAL (TRANSGLACIAL) LANDSCAPES IN THE KARAKORUM MOUNTAINS Dr. Lasafam Iturrizaga Earth Surface Research Group School of Earth Sciences and Geography Keele University, UK e-mail: liturri@gwdg.de

The Karakoram Mountains (72°-79°E/35°36°N) are characterized by their high volume and variety of debris accumulations. In the classical view of geomorphology, talus cones in high mountain areas are mainly classified as periglacial landscape elements ànd considered as products of frost weathering processes.

However, field investigations in over twenty Karakoram valleys showed that the major part of slope deposits has a glacial origin.

Therefore its distribution and genesis is closely linked to the Last Glacial Maximum and Lateglacial glaciation extent. Those paraglacial (transglacial) sediments can be used to reconstruct the minimum trimlines of glaciation (Fig. 1).

Despite the intensive weathering processes in this subtropcial mountain range, secondary debris production, i.e. the redeposition and reshaping of glacial sediments, exceeds primary debris production. The current rate of debris production is turning out to be too low to account for the huge volumes of debris presently blanketing the rock slopes 22

up to 1000 m above the valley floor. High morphodynamics in the mountain relief primarily contribute to the remobilization of ancient unconsolidated slope moraines leading to convergent forms with periglacial talus cones. In order to comprehend the genesis and age of those debris accumulations it is necessary to consider the position-specific topographical relationship of the debris accumulations to the corresponding stages of glaciation. The presentation will highlight the main types and characteristics of paraglacial landforms and focus on the aspects which disagree with the frost weathering paradigm.

References Iturrizaga, L. (1995): The evolution of debris accumulations in response to the former glaciation in the Karakorum and Himalaya. In: Terra Nostra, Schriften der Alfred-Wegener-Stiftung 2/95, 242.

Iturrizaga, L. (1999a): Die Schuttkörper in Hochasien - Eine geomorphologische Bestandsaufnahme und Typologie postglazialer Hochgebirgsschuttkörper im

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Hindukusch, Karakorum und Himalaya.

In: Gรถttinger Geographische Abhandlungen Band 106, 326 pp.

Iturrizaga, L. (1999b): Typical debris accumulation forms and formations in High Asia. A glacial-history-based concept of the origin of Postglacial debris accumulation landscapes in subtropical high mountains with selected examples from the Hindu Kush, the Karakoram and the Himalayas. In: GeoJournal, Tibet and

High Asia V, vol. 47, 277-339.

Iturrizaga, L. (in press): Paraglacial (transglacial) landforms in the Karakoram.

In: Kreutzmann, H. (Ed.) Karakoram in Transition. 18 pp.

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Shifting Lands. New insights into periglacial geomorphology

Paraglacial Session Oral Paper

THE IMPORTANCE OF ROCK-SLOPE FAILURE IN THE HIGHALPINE PARAGLACIAL SYSTEMS. EXAMPLES FROM UPPERDURANCE AREA (SOUTHERN ALPS OF FRANCE) Etienne Cossart1, Didier Bourlès, R. Braucher, Monique Fort1 Université de Paris 7 - eedc79@aol.com

1

In high-mountains morphodynamic system, consequences of glacial dynamics are of wide variety. For example they erode the substratum, steepening the slopes to shape a trough valley. They both erode and guarantee substratum stability as they buttress the slopes, applying on them a strength proportional to their thickness. As a consequence the glacial shrinking may destabilize entire slopes. My proposal is to understand how the slopes react to glacial debuttressing. To realize this study we compare the paraglacial evolution of slopes in two catchments (La Clarée and Vallouise), situated in Upper Durance catchment, but in different geological settings.

In Upper Durance, during the Late Glacial Maximum the palaeo-glacier reached a 1000meter thick. Its disappearance had generated an important debuttressing, which values were estimated around 100.103 Pascals.

In the Vallouise catchment, relief is characterized by large and steep slopes sustained by crystalline rocks (granite, gneiss). Only few rock-failures had occurred, but they are of large magnitude, and the deposits associated (volume around 106 m3) had dammed the valley. Their release is due to high debuttressing values, steep slopes and the presence of faults or joints 24

weakening the bedrock. Consequently, these deposits have constrained fluvial dynamics, trapping sediments upstream them. So, fluvial adjustments (for example due to glaciations post-LGM and to climatic change) are sensitive in the upper catchment.

In the Clarée catchment, relief is both less steep and high than in Vallouise, the geological setting is characterized by sandstone outcrops. Spatially the frequency of rock collapses is high, but they are of low magnitude. The deposits of these collapses were not sufficient to dam the valley, and they haven’t constrained the fluvial dynamics.

The nature of rock collapses has constrained recent fluvial dynamics. After the LGM many glacial advances occurred (the last one is the Little Ice Age) and the fluvial system have been influenced by those glacial/paraglacial cycles.

In the Vallouise catchment, the responses of the fluvial system are sensitive in the upper part, upstream the rock-failures deposits, where sediments are preferentially trapped while in the Clarée catchment the responses are sensitive all over the catchment.

To conclude we insist on the fact that rockfailures due to LGM paraglacial adjustments have conditioned the fluvial post-LGM paraglacial responses.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Paraglacial Session Oral Paper

IMPACTS OF CLIMATIC CHANGE ON DEBRIS FLOWS DYNAMICS IN THE FRENCH ALPS (MASSIF DES ECRINS): RECENT AND PROSPECTIVE ANALYSIS. Vincent Jomelli 1, Daniel Brunstein 1, David Grancher 1, Pierre Pech², M. Deque 3, L. Terray 4 CNRS UMR 8591, 1 place A. Briand 92915 Meudon France Université Paris I Panthéon-Sorbonne 3 Météo France CNRM/GMGEC/EAC 4 CERFACS 1 2

The progressive increase in socio-economic activity in the Alps is resulting in an increasing potential risk from natural hazards such as debris flows at a time when changes in climate may be altering the frequency of such mass movements. Nevertheless, quantifying the impacts of climatic change on such process remains a serious problem. From a framework of meteorological stations and different scenarii from two high resolution GCM model outputs realized by Meteo-France and Cerfacs for the end of the next century, and a dataset of 350 debris flows deposits extracted from a GIS database and dated since 1952, we test

the impacts of these actual and future climatic change on debris flows dynamic in the French Alps. Triggering frequency probabilities are estimated from different stochastic models.

These models show a climatic effect for these last 40 years. The frequency of intense rainy events controls the triggering on the short time scale. On a larger scale, we show an effect of freezing days which summarize stock reconstitution of the volume of debris stored between two debris flows. Finally, we realized a prospective analysis with climatic scenarii based on the IPCC hypothesis.

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Shifting Lands. New insights into periglacial geomorphology

Paraglacial Session Oral Paper

RUNOFF IMPACT ON PLANT COLONIZATION ON THE FOREFIELD OF MIDRE LOVÉNBREEN, SPITSBERGEN (79°N) SINCE THE END OF THE LITTLE ICE AGE Myrtille Moreau1, Denis Mercier² Dominique Laffly3, Erwan Roussel1 Université Blaise-Pascal Clermont II, UMR 6042 CNRS Maison de la Recherche, 4 rue Ledru, 63057 ClermontFerrand et Institut Polaire Français Paul-Émile Victor. E-mail : myrtille.moreau@free.fr ² Université Paris IV-Sorbonne, 191 rue Saint Jacques, 75005 Paris, UMR 6042 CNRS et Institut Polaire Français Paul-Émile Victor. E-mail : denis.mercier@paris4.sorbonne.fr 3 Université de Pau, avenue du Doyen Poplawski, 64000 Pau, UMR 5603 CNRS et Institut Polaire Français PaulÉmile Victor. E-mail : dominique.laffly@univ-pau.fr 1

Climatic changes that took place since the end of the Little Ice Age have considerably disturbed environmental balances in the high latitudes. In Spitsbergen (79°N) (Svalbard archipelago) valley glaciers moved back ca. 1 km in one century. In the recently deglaciated areas, new paraglacial processes have been acting on the landscape. They are accompanied by plant colonisation, the dynamics of which correlates with the increase through time of plant cover and floristic diversity. The paraglacial dynamics, however, contribute with runoff to the instability of the sedimentary deposits at different time and

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spatial scales and partly destroy the plant cover. There is thus a strong interactive link between postglacial morphogenic process and plant dynamics. The present studies were carried out in the Midre Lovénbreen foreland at Brøggerhalvøya in Spitsbergen during 2001 and 2002. They allowed us to establish a chronology of plant colonisation in deglaciated areas in relation to the level of instability of the geomorphic environments.

Key words: Little Ice Age, runoff, plant colonisation, paraglacial, proglacial area, Spitsbergen.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Paraglacial Session Oral Paper

HOW SIGNIFICANT IS THE DISTINCTION BETWEEN PARAGLACIAL AND SEISMO-TECTONICALLY INDUCED MASSMOVEMENTS IN ACTIVE OROGENS? INSIGHTS FROM THE PAMIR-KARAKORUM-HIMALAYAN RANGES Monique Fort Université de Paris 7 Denis-Diderot

Research dealing with the paraglacial concept of fluvial readjustment during and after deglaciation (Church and Ryder, 1972) has been extended to embrace the entire geomorphic system, as recently pointed out by Ballantyne (2002). In the case of tectonically active orogens, the definition of paraglacial landscapes as « directly conditioned by glaciation and deglaciation » is challenged, in respect of the resultant landforms and geomorphic activity, by the potential risk of confusing paraglacial (in sensu stricto) processes with those arising from indirect tectonic responses. This is particularly true in the case of large massmovements, features commonly observed in the formerly extensively glaciated PamirKarakorum-Himalayan ranges, where relative relief is at a maximum. Several questions arise. What is the exact origin of the very steep slopes - glacial excavation,

or fluvial incision driven by uplift? What is the primary control on large rock failures; are they debuttressing-induced during and after deglaciation, or seismically-induced by tectonic activity? In the latter context, how can a potential delayed paraglacial response on a rock slope be accounted for if, at any time, slope collapse is likely to occur in response to rock-mass stress release? These questions are addressed here using selected examples derived from various situations encountered in the Pamir-Karakorum-Himalayan orogenic system. It is concluded that, in contrast to other well-documented processes (reworking of sediment-mantled slopes and deposition of paraglacial debris-cone, alluvial fans and some valley fills), it appears that assertions claiming a paraglacial origin for most, if not all, of the large rock-slope failures observed in this orogen cannot be sustained.

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Shifting Lands. New insights into periglacial geomorphology

Weathering Session Oral Paper

BLOCKFIELDS OF GASPÉ PENINSULA : ORIGINE AND AGE Cécile Tsao Centre d’Études Nordiques Pavillon Abitibi-Price Université Laval Sainte-Foy, Québec CANADA, G1K 7P4

On the rigth river of the St Lawrence estuary, the higher summits of the Mounts Chic-Chocs reach an altitude of 1 200 m. Some mountains are mantled by blockfields between 0,6 to 3 m thick, covering the summit and the slopes. On gaspesian mountains, blockfields consisting of a complete cover of decimetric boulders with no visible fine soil and very patchy vegetation cover.

As the Gaspé peninsula has been overridden by the Laurentian ice sheet during the last glaciation, blockfields of the Chic-Chocs mountains are in the center of the discussion about the vertical extent of the quaternary glaciations (Lebuis and David 1977; David and Lebuis 1985; Occhietti 1989; Hétu and Gray 2000). Furthermore, this discussion is based on two unresolute problemes : the age and the origine of blockfields (Ives 1958; Loken 1962; Sugden and Watts 1977; Gangloff 1983; Ballantyne 1998). Several observations may indicate that gaspesian blockfields can’t be used to determine the vertical extent of ice masses at the last glacial maximum.

First, the thickness of blockfields increase downwards away from the summits, implying that blocks have gradually moved along the slopes. This hypothesis is supported by a 28

second observation : a thick layer of blocks on a geologic contact, and the presence of blockfields on presumed quaternary deposits at the slope foot. We conclude from these constatations that gaspesian blockfields can’t be used as a indicator of nunataks. Moreover, the presence of erratics attest the passage of an ice sheet on the summits. Whilst it is true that erratics are sometimes lying on blockfields, other considerations indicate that most debris cover result from in situ weathering. For example, the composition of blockfields generally reflects that of the underlying bedrock. Furthermore, sections cut through blockfields often exhibit a vertical transition from intact rock trhough imbricated to loosened rock fragments and finally chaotic block mantle. There is also a vertical contrast in the roundness of exposed and buried clast. The roundness appearance of exposed rock, in comparaison with angular blocks in profoundless may be an effect of granular desintegration. This contrast tends to demonstrate that granular desintegration responsible for rounding exposed clast surface postdates the development of the blockfields itself, and therefore occurred during the Holocene. The roundness of exposed clast

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

may also indicates a chimic dissolution under an ancient forest cover. Buried organic horizons suggest that very patchy and fragmented forest result from fire episods.

References Ballantyne, C. K. (1998). “Age and significance of mountain-top detritus.” Permafrost and Periglacial Processes 9(4): 327-345.

David, P. P. and J. Lebuis (1985). Glacial maximum and deglaciaition of western Gaspé, Québec, Canada. Late Pleistocene History of Northern New England and adjacent Québec. H. W. Borns, P. LaSalle and W. B. Thompson, Geological Society of America, Special Paper. 197: 85-109.

Gangloff, P. (1983). “Les fondements géomorphologiques de la théorie des paléonunataks : le cas des Monts Torngats.” Zeitschrift für Geomorphologie, Supplementband 47: 109-136.

Hétu, B. and J. Gray (2000). “Les étapes de la déglaciation dans le nord de la Gaspésie (Québec) : les marges glaciaires des Dryas ancien et récent.” Géographie Physique et Quaternaire 54(1): 5-40.

Ives, J. D. (1958). “Moutain-top detritus and the extent of the last glaciation in northeastern Labrador-Ungava.” The Canadian Geographer 12: 25-31.

Lebuis, J. and P. P. David (1977). “La stratigraphie et les événements du Quaternaire de la partie occidentale de la Gapésie.” Géographie Physique et Quaternaire 31(3-4): 275-296.

Loken, O. (1962). “On the vertical extent of glaciation in northeastern Labrador - Ungava.” Canadian Geographer 6(3-4): 106-119.

Occhietti, S. (1989). Géologie quaternaire de la sous-région de la vallée du SaintLaurent et des Appalaches. Le Quaternaire du Canada et du Groenland. chap. 4, R.J. Fulton, Commission Géologique du Canada. vol. 1: 374-416.

Sugden, D. E. and S. H. Watts (1977). “Tors, felsenmeer and glaciation in northern Cumberland Peninsula, Baffin Island.”

Canadian Journal of Earth of Sciences 14: 2817-2823.

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Shifting Lands. New insights into periglacial geomorphology

Weathering Session Oral Paper

STONE RUNS IN THE FALKLAND ISLANDS : PERIGLACIAL OR TROPICAL ?

Marie-Françoise André 1, Kevin Hall 2, Joselito Arocena 2 Laboratory of Physical Geography, GEOLAB-UMR 6042-CNRS, Blaise Pascal University, 4 rue Ledru 63057 ClermontFerrand Cedex 1, France E-mail : m-francoise.andre@univ-bpclermont.fr 2 Geography Program, University of Northern British Columbia, 3333 University Way, Prince George, BC, Canada V2N 4Z9 E-mail : hall@unbc.ca ; arocenaj@unbc.ca 1

The Falkland Islands were not been glaciercovered (except for a few cirque glaciers) during Pleistocene cold phases but did experience long-lasting periglaciation. In this context, stone runs, that are striking quartzite block streams covering hundreds of km2, were previously interpreted as typically periglacial features, reflecting intense frost wedging of exposed rock surfaces during the Quaternary. Indeed, they present large morphological similarities with various types of rock-rubble material found in past and present cold-climate environments, including block fields (= Felsenmeer) and stone rivers (= rivières de pierres).

A preliminary field study of some stone runs located between Stanley and PortLouis leads to a different interpretation.

Whereas superficial microfeatures such as stone stripes, stone circles and individual uptilted stones can be justifiably attributed to frost sorting and frost heaving processes under Quaternary periglacial conditions, the origin of the constitutive angular rockrubble is here suggested to be tropical. This 30

interpretation is based on the finding of widespread rubefaction phenomena affecting both the angular quartzite fragments of the stone runs (that appear to belong to rather thin though impressive pavements) and the underlying heterometric material including fine-grained matrix. This two layer system might represent the truncated roots of a pre-Quaternary weathering profile, as early suggested by Caine (1968) for block fields of Tasmania. Laboratory analyses are in progress and further field investigations are required, but if confirmed, the tropical origin of the Falklands stone runs would be a new milestone in support of the antiquity of part of the high latitude block fields whose some are known to have survived several glacial episodes (Kleman J. & Borgström I., 1990).

References Caine N., 1968. The fabric of periglacial blockfield material on Mt. Barrow, Tasmania.

Geografiska Annaler 50A (4), 193-206.

Kleman J. & Borgström I., 1990. The boulder fields of Mt. Fulufjället, West-Central Sweden. Geografiska Annaler 72A, 63-78.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Weathering Session Oral Paper

CHEMICAL AND BIOLOGICAL WEATHERING OF GRANITIC TORS IN ARCTIC FINLAND Matti Seppälä, Sean Campbell, Robert G. Darmody, Colin E. Thorn University of Helsinki University of Kentucky University of Illinois

Two granitic tors located at Pyhä-Nattanen (27E 22.207’E, 68E 07.335’ N) and Riestovaara (27E 09.003’ E, 68E 02.613’ N) in Arctic Finland were sampled comprehensively and material for cosmogenic dating obtained from their summits. At Pyhä-Nattanen the sampling sequence includes bedrock material and grus taken from within horizontal cracks which are so prevalent at the site as to make it resemble a stack of pancakes. At Riestovaara bedrock and grus samples were also collected, but in this case are also supported by a sample set extracted from a shallow pit dug in an embryonic soil forming on the bedrock

surface at the outcrop. In both instances, the availability of a cosmogenic date from the top of the tor provides an estimate of the time available for development of the weathering reported assuming that the rock was fresh at the time of most recent exposure. Analyses include comprehensive chemical evaluation of all materials, a complete pedogenic analysis of the soil at Riestovaara, plus a systematic analysis of the chemical and biological processes producing rock weathering at both sites using Scanning Electron Microscopy (SEM).

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Shifting Lands. New insights into periglacial geomorphology

Weathering Session Oral Paper

L’INFLUENCE RESPECTIVE DES PROCESSUS PÉRIGLACIAIRES ET DES PROCESSUS GLACIAIRES DANS L’ÉLABORATION DES FELSENMEERS DE MONTAGNES DE L’EUROPE DU NORDOUEST. Dominique Sellier Institut de Géographie et d’Aménagement régional de l’Université de Nantes UMR 6042-CNRS et UMR 6554-CNRS Rue de la Censive du Tertre BP 81227 44312 Nantes cedex 3 France

Les restes de surfaces d’aplanissement situés au sommet des montagnes de l’Europe du Nord-Ouest, ou à proximité de ces sommets, comportent des champs de blocs qui ont suscité plusieurs explications impliquant des processus glaciaires, des processus périglaciaires supraglaciaires et des processus périglaciaires postglaciaires.

L’observation d’une centaine de sommets de montagnes du Spitsberg, de Norvège, d’Ecosse et d’Irlande du Nord, conduit à interpréter la majorité de ces champs de blocs comme des champs de gélivation, qui ont été élaborés au-dessus des niveaux d’englacement pléistocènes, tout au moins du niveau supérieur de l’englacement weichselien, et qui ont éventuellement continué à subir une morphogenèse périglaciaire en périodes interglaciaires, du fait de leurs altitudes.

Ces “champs de blocs d’origine périglaciaire supraglaciaire”, auxquels pourrait être réservé le terme de “felsenmeers s.s.”, se caractérisent en effet par trois propriétés reconnues : - les nombreux témoignages de processus périglaciaires hérités (soulèvement gélival 32

et gélifraction in situ, structures polygonales de dimensions plurimétriques et de texture openwork, distinctes de figures périglaciaires fonctionnelles, plus réduites et plus localisées), - les signes d’une longue exposition aux agents météoriques (subangulosité des blocs, formation de vasques et livraison d’une matrice sableuse ou argilo-sableuse), - l’absence d’héritages glaciaires notoires, en dehors de blocs erratiques éventuels, rares et dispersés, caractérisés par un arrondi significatif de leur origine et par une désagrégation superficielle significative de leur météorisation.

Ces felsenmeers s.s., d’origine périglaciaire supraglaciaire, jalonneraient des paléonunataks weichseliens ou préweichseliens.

Ils s’opposent à des formations moins étudiées, correspondant à des champs de blocs d’origine glaciaire, situés en contrebas des précédents, sur des replats, revers, ou versants peu inclinés.

Hormis leurs conditions de site, ces champs de blocs se différencient des felsenmeers précités par quatre propriétés principales :

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

- l’abondance des blocs arrondis, à émoussé glaciaire caractéristique, - la fréquence des erratiques hétérométriques et pétrographiquement hétérogènes, - une matrice sablo-caillouteuse qui détermine une texture souvent fermée, - mais aussi les marques d’une gélidivision in situ, de densité croissante avec l’altitude, qui distinguent formellement ces champs de blocs d’origine glaciaire, mais progressivement défigurés par les processus périglaciaires postglaciaires, des dépôts morainiques ordinaires.

Les propriétés et les conditions d’évolution de ces “champs de blocs d’origine morainique” suggèrent qu’une partie des “felsenmeers s.s.”, à blocs erratiques dispersés et altérés, situés en amont, dérivent de champs de blocs analogues, corrélatifs de glaciations plus anciennes et plus étendues en altitude.

Les observations de terrain ont conduit à identifier un troisième type de champs de blocs, plus rare que les deux précédents en raison des conditions exigées par sa genèse et par sa conservation. Ces champs de blocs, situés sur des paliers topographiques ou des niveaux d’érosion étagés, s’intercalent entre les deux précédents, sans s’éloigner beaucoup des sommets. Ils se distinguent d’abord par un assemblage de blocs hétérométriques et anguleux, enchevêtrés et souvent instables, à texture le plus souvent openwork. Ils se caractérisent surtout par une triple série de propriétés : - la présence effective, mais accessoire, de vieux erratiques épars et très altérés, comparables à ceux qui demeurent sur les felsenmeers s.s. et qui, comme eux, peuvent jalonner de très anciens niveaux d’englacements pléistocènes, - la présence d’héritages glaciaires récents, notamment de vides d’arrachement ou

de délogement à partir des affleurements rocheux éventuels, de blocs perchés exemplaires disposés sur ces affleurements ou à la surface des champs de blocs, de traces de déplacements glaciaires sur les affleurements et sur les blocs (stries, broutures), - les marques, secondaires, de processus périglaciaires postglaciaires, sinon fonctionnels (gélifraction, ostioles, cercles de pierres).

La rareté des héritages périglaciaires et l’angulosité des blocs dissocient ces formations des felsenmeers s.s.. L’absence d’un fond morainique authentifié et celle d’une matrice abondante les dissocient tout autant des champs de blocs d’origine morainique.

Leur fréquente disposition en contrebas de felsenmeers s.s. et les témoignages évidents d’actions glaciaires relativement récentes conduisent à considérer ces formations comme des “felsenmeers de marge supraglaciaire”, élaborés sous une couche de glace mince, en contrebas de nunataks éventuels. Reconnus pour l’instant sur une dizaine de montagnes de Norvège et d’Ecosse, ils fourniraient un moyen d’identifier les niveaux supérieurs d’englacements pléistocènes ou de les vérifier.

Les propriétés de ces “felsenmeers de marge supraglaciaire” suggèrent ainsi que certains des “felsenmeers s.s.” situés en amont dérivent aussi de champs de blocs de ce type, et héritent, pour partie, des effets directs d’une érosion glaciaire sur le substratum.

Cette typologie fournit une illustration supplémentaire des relations entre processus périglaciaires et processus glaciaires dans l’espace et dans le temps, à propos de l’élaboration des champs de blocs des montagnes de l’Europe du Nord-Ouest.

33

Shifting Lands. New insights into periglacial geomorphology

Weathering Session Oral Paper

POST-GLACIAL WEATHERING FORM AND PROCESS IN A PERIGLACIAL ENVIRONMENT, HARDANGER PLATEAU, SOUTHERN NORWAY Dawn T. Nicholson*, Frank H. Nicholson Department of Environmental and Geographical Sciences Manchester Metropolitan University Chester Street Manchester, UK. E-mail: d.nicholson@mmu.ac.uk Tel: 0161 247 6232 *

The broad aim of this research is the investigation of post-glacial weathering on the Hardanger Plateau in southern Norway.

Specific interests are the relative influence of post-glacial chemical and mechanical weathering processes, the determination of post-glacial weathering rates and the identification of relationships between form and process at all scales. This is being achieved through analyses of the geochemistry, lithology, micro-structure and micro-morphology of ice-smoothed surfaces. In addition, attempts are being made to characterise the macro-fractures and morphology of r么che moutonn茅e and their relationship to the coarse, angular weathering product which is ubiquitous here.

little soil development and a high percentage of bare rock. The area has been affected by glaciation as recently as 10,000 years ago, but there may have been localized glaciers in the highest areas in the Little Ice Age.

The work is based on several study locations, comprising approximately 5km2 in the south west corner of the Hardanger Plateau in southern Norway (53oN) at altitudes ranging from 1200 to 1450m. This region experiences a mean annual temperature of -2oC and mean annual rainfall of 1000mm. The plateau supports sparse tundra vegetation and there is

Evidence for chemical weathering includes the presence of pseudokarren on granitic gneiss such as rounded solution pits up to 80cm in length and 10cm in depth. They have much the same appearance as the rundkarren observed in limestone terrain and may represent a meso-scale version of solution features found at the micro-scale by Dixon et al (2002). Rock

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The region is dominated by a mantle of angular debris which appears to be the product of frost shattering. The debris looks very fresh, though this is partly due to the lack of lichen cover. However, examination of icescoured surfaces reveals evidence of chemical weathering. There is increasing evidence and argument that chemical processes contribute much more to weathering in cold regions than previously thought (Dixon et al 2002, Hall et al 2002).

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

surfaces are commonly discoloured and have weathering rinds typically 5mm thick and up to 30mm thick on fracture surfaces. Work is under way to determine if this discolouration represents the same solutional loss of key mineral constituents as found by Dixon et al (2002). Rarely, there are examples of deeply penetrative mineral decomposition. Many ice-smoothed rock surfaces display small scale surface spalling and rounded fracture edges.

These may involve mechanical processes, but discolouration associated with them suggests chemical weathering is also active.

Preliminary results from a study of ice polished quartz veins (using the method of Dahl, 1967) indicate an average rate of postglacial lowering of 0.8mm ka-1, with a range from 0.0 to 2.3mm ka-1 for different locations (based on nearly 400 measurements). These results are comparable with those obtained

by André working on a similar range of rocks in the Abisko Riksgränsen region in north Norway (André 1995, 1996, 2002).

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Shifting Lands. New insights into periglacial geomorphology

Weathering Session Oral Paper

WEATHERING OF GRANITE AROUND THE SUMMIT OF DENALI (MT. MCKINLEY), ALASKA, USA Kenji Yoshikawa Water and Environmental Research Center Institute of Northern Engineering University of Alaska Fairbanks PO Box 755860 Fairbanks Alaska 99775-5860 Phone & Fax 907-474-6090 E-mail ffky@uaf.edu

Weathering processes are examined around the summit of Denali (Mt. McKinley) (6194m) by using in-situ rock surface temperature, wind direction and speed, scanning electron microscopy (SEM), Energy Dispersive Spectrometry (EDS), X-Ray Diffraction (XRD) analysis and remote sensing techniques (Airborne Visible/Infrared Imaging Spectrometer:AVIRIS). Weathering processes are very slow and dominated by frost action and varnish. The effective freezethaw cycles were recorded 63 times at the south facing wall and 30 times at the north facing wall between 2002 and 2003. The daily rock surface temperature fluctuated more than 30ÂşC, which strongly stresses the mineral grains in the granite. However, neither granular disintegration nor micro-sheeting were commonly observed. The rock wall is partly coated with a reddish-brown oxidized film. This process is observed to be different from place to place on the same granite unit.

Slope and aspect are not strong factors in the varnish process. North facing and south facing 36

walls of the bedrock displayed similar spectral properties in the near infrared wave length (750 – 2500 nm) range. Frost shattering and varnishing of rocks are controlled by surface temperature, moisture, and the physical properties of the rock. One of the important control agents in this study area was moisture availability, given the same bedrock and effective freeze-thaw cycle. Snow particles, moved by strong winds, bring moisture to the rock during summer period. The maximum wind speed was recorded at 82.5 m/sec on July 22, 1995 at the weather station (5715m) near Denali Pass. Strong winds (>50 m/sec) are commonly sustained more than a day by the jet stream circulations. Severe rock varnish was observed on the west and southwest facing walls and higher than 4500m at the West Buttress and Cassin Ridge.

Very little varnish was observed around the Harper Glacier and North Peak (5934m). The severity of the varnish is influenced by the wind direction during summer periods and the snow particle size.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Weathering Session Oral Paper

SEDIMENTARY SOURCE-TO-SINK-FLUXES IN ARCTIC-OCEANIC SWEDISH LAPLAND – RESULTS FROM PROCESS GEOMORPHOLOGICAL INVESTIGATIONS AT THE LANDSCAPE LEVEL Achim A. Beylich Geological Survey of Norway N-7491 Trondheim, Norway Achim.Beylich@ngu.no

The Latnjavagge drainage basin (ca. 9 km²; 950-1440 m a.s.l.; 68°20`N, 18°30`E) is a representative catchment for the higher mountain area in the Abisko region in northernmost Swedish Lapland. The analysis of sediment fluxes, denudation rates, sediment sinks and sediment budgets in fluvial drainage basins forming clearly defined landscape units are major elements for the interpretation of landscape evolution. The comparison of denudation rates and sediment budgets in representative drainage basins in present periglacial environments with given morphoclimatic, topographic, lithological/ geological and ecological features can give insight into the internal differentiation of the present-day periglacial environments. To cast further light upon present-day denudation rates and relationships between chemical and mechanical denudation in periglacial environments, a sediment budget study was initiated in Latnjavagge in 1999. Denudative slope processes, mechanical fluvial denudation, delta and lake sediments and chemical

denudation have been analysed. The mean annual chemical denudation rate in the entire catchment is 5.4 t km-2yr-1. Mechanical fluvial denudation is slightly lower than chemical denudation and appears to be the second most important geomorphological process type regarding annual mass transfers [t m yr-1].

Most fluvial sediment transport in creeks occurs within a few days during snowmelt generated runoff peaks. The calculated mean mechanical fluvial denudation rate at the inlet of lake Latnjajaure (0.73 km²), situated in Latnjavagge close to the catchment outlet, is 2.3 t km-2 yr-1. At the outlet of the entire Latnjavagge drainage basin, situated below lake Latnjajaure, the mean annual mechanical fluvial denudation rate is only 0.8 t km-2yr-1.

Analysis of the volume of the delta of lake Latnjajaure and additional corings of lake sediments document little Holocene sediment accumulation in the Latnjajaure delta and in the five lakes in Latnjavagge.

The relatively most important denudative slope processes regarding annual mass 37

Shifting Lands. New insights into periglacial geomorphology

transfers are rock- and boulder falls.

Nevertheless, the thicknesses of material accumulated below rockwalls, rockledges etc. within the slope systems reach only at some localities more than a few metres. Today, both chemical and mechanical denudation are of low intensity. Because of the low intensities of denudative processes, both today and during the Holocene, Postglacial modification of the glacial relief is altogether negligible. At the landscape level, there has been no adjustment of the Pleistocene glacial landforms to the denudative processes which have been operating during the Holocene. Today, there is no equilibrium between landforms and denudative processes operating under the present-day vegetation cover and the presentday arctic-oceanic morphoclimate.

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The low present-day intensities of denudative processes with a low frequency of debris flows and slides and very little wash denudation at the slope systems are to a large extent due to the very stable vegetation cover and the closed rhizosphere which have developed below 1300 m a.s.l. in the entire catchment area. Local disturbances of the vegetation cover and rhizosphere caused by present-day direct human impacts like extensive reindeer grazing (reindeer husbandry), some hiking tourism and field research at LFS are of minor importance and do not significantly affect the present-day denudative process rates and the present-day sediment budget of the drainage basin.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Weathering Session Oral Paper

INFLUENCE OF MOISTURE IN ROCK WEATHERING IN COLD CLIMATES Christine Elliott PhD Candidate Department of Geography University of Canterbury Private Bag 4800 Christchurch New Zealand Email: c.elliott@geog.canterbury.ac.nz

The importance of moisture in determining which rock weathering processes may operate, as well as the rate at which rock weathering occurs, has long been recognised. Despite this there has been no systematic study of how increasing quantities of moisture may influence the type of process operating. In addition, few attempts have been made to quantify the influence of changing moisture availability on weathering rates. This paper describes the results of recent research to measure the frequency of moisture fluctuations on granite rock surfaces at four locations in Victoria Land, Antarctica. Moisture levels at 45 mm and 90 mm depth within the rocks were also recorded and used to determine the moisture levels required for simulated weathering rate experiments in the laboratory.

Initial results from two sites show that moisture reaches the surface of the rock more frequently than might initially have been expected in this dry climate (Figure 1).

The subsurface measurements indicate for the first time how moisture varies with depth.

Although levels are low, for example between 3.3 and 5.4 gm/m3 at 45 mm depth for the Victoria Valley in January 2003, these results show that average levels differ between the beginning and the end of the summer season at both depths. In addition, they fluctuate during the course of a 24-hour period so that at times the moisture levels increase with depth whereas at other times they decrease.

The average moisture levels of small rock blocks recorded in other studies do not identify these differences with depth.

Preliminary results of the relationship between moisture levels and weathering rates will also be presented.

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Shifting Lands. New insights into periglacial geomorphology

Figure 1. Hourly surface moisture results for the north-facing Victoria Valley site between 30th October 2002 and 25th January 2003 indicating the times, frequency and magnitudes of these events

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Weathering Session Oral Paper

ROCK WEATHERING BY THERMAL STRESS: OBSERVATIONS FROM THE ANTARCTIC AND CRITICAL DISCUSSION Jan Boelhouwers Department of Earth Sciences Uppsala University Sweden

In recent years several papers have advocated the importance of short term temperature fluctuations in promoting weathering at the rock surface. This study discusses the potential role of thermal stress in the light of observations on blockfields and high resolution temperature records from basalt nunataks near Wasa station (73oS, 13oW).

Blockfields in dolerite at Wasa station are typically highly angular whereas blocks on nearby Fossilryggen in medium-grained basalt are highly rounded. Rock temperature records show i) high rates of surficial temperature changes well in excess of the reported threshold of 2oC/min, ii) a maximum diurnal warming not at but some distance below the surface, iii) rapid disappearance of thermal fluctuations within cm below the surface.

The role of thermal stress in producing large blocky material relies on the potential for longer duration (diurnal to seasonal) temperature fluctuations to produce sufficient stress to overcome the tensile strength of the rock mass. Recent observations of lateral displacement of surfaces of salt mountains in Iran support such a hypothesis for hot desert environments (Safaei, 2001; Talbot and Aftabi, 2004).

The role of rapid temperature fluctuations at the rock surface is argued by Hall and AndrĂŠ (2003) to promote surficial disaggregation and flaking. This could argue for a more rapid surficial weathering rate in the coarse grained basalt, leading to a rounded surface appearance.

However, in the light of the findings by Chen and Chi-yuen (1980) considerations should be given to the importance of absolute temperature, the significance of a 2oC/min threshold and hysteresis effects.

Chen, Y. and Chi-yuen, W., 1980: Thermally induced acoustic emission in westerly granite, Geophysical Research Letters, 7, 1089-1092.

Hall, K. and AndrĂŠ, M-F., 2003: Rock thermal data at the grain scale; applicability to granular disintegration in cold environments. Earth Surface Processes and Landforms, 28, 823-836.

Safaei, H., 2001: Elastic diurnal movements of masses of Tertiary salt extruded in north central Iran, Journal of Science of the Islamic Republic of Iran, 12, 241-250.

Talbot, C. and Aftabi, P. 2004: Geology and models of salt extrusion at Qum Kuh, central Iran, Journal of the Geological Society, London, 161, 321-334.

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Shifting Lands. New insights into periglacial geomorphology

Paraglacial and Weathering Poster Session

ARCTIC COASTAL DYNAMICS (ACD) – OVERVIEW OF AN INTERNATIONAL RESEARCH PROGRAM Volker Rachold and the ACD Group Alfred Wegener Institute Potsdam, Germany vrachold@awi-potsdam.de

The coastal zone is the interface through which land-ocean exchanges in the Arctic are mediated and it is the site of most of the human activity that occurs at high latitudes.

The Arctic coastlines are highly variable and their dynamics are a function of environmental forcing and coastal geology, geocryology and morphodynamic behavior (Figure 1).

Coastal processes in the Arctic are strongly controlled by Arctic-specific phenomena, i.e. the sea-ice cover and the existence of onshore and offshore permafrost. During the winter season comprising 7-8 months a thick and extensive sea-ice cover protects the coastline from hydrodynamic forcing. During the open water season, mainly after break-up in spring, the sea-ice is an important transport agent for coastal sediments. The Arctic coastal region is the transition zone between onshore and offshore permafrost and the degradation of permafrost, which can be connected with the release of permafrost-bond greenhouse gases (GHG), is concentrated in the coastal zone. During the short ice-free period, the unlithified ice-rich, permafrost-dominated coastlines are rapidly eroded and the resulting coastal sediment, organic carbon, and nutrient fluxes play an important role in the material 42

budget of the Arctic Ocean. Global and regional climate changes will significantly affect physical processes, biodiversity and socio-economic development in the Arctic coastal areas.

Arctic Coastal Dynamics (ACD) is a multidisciplinary, multi-national project of the International Arctic Science Committee (IASC) and the International Permafrost Association (IPA) which aims to: • establish the rates and magnitudes of erosion and accumulation of Arctic coasts and to estimate the amount of sediments and organic carbon derived from coastal erosion; • develop a network of long-term monitoring sites including local communitybased observational sites; • refine and apply an Arctic coastal classification (includes ground-ice, permafrost, geology, etc.) in digital form (GIS format) and produce a series of thematic and derived maps (e.g. coastal classification, ground-ice, sensitivity etc.); • compile, analyze and apply existing information on relevant environmental forcing parameters (e.g. wind speed, sea-level, fetch, sea ice etc.); • identify and undertake focused research

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

on critical processes; • develop empirical models to assess the sensitivity of Arctic coasts to environmental variability and human impacts.

Currently, ca. 25 institutions from Austria, Canada, Germany, Norway, The Netherlands, Russia, Switzerland, UK and USA are contributing to the ACD project. This presentation provides an overview of the research activities and the latest results of the ACD project.

Figure 1. Arctic coastal processes and responses to environmental forcing.

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Shifting Lands. New insights into periglacial geomorphology

Paraglacial and Weathering Poster Session

PARAGLACIAL DYNAMICS IN SVALBARD (Pr. 400 – Geomorphoclim –French Polar Institute Paul-Émile Victor) Denis Mercier1 & 2, Marie-Françoise André2, Samuel Étienne2, Dominique Laffly3, Myrtille Moreau2, Dominique Sellier4, Joëlle Dupont5, Angélique Prick6, Grzegorz Rachlewicz7.

- Université Paris IV – Sorbonne - UMR 6042 CNRS – Géolab – Clermont-Ferrand 3 - Université de Pau et des Pays de l’Adour 4 - Université de Nantes 5 - Muséum National d’Histoire Naturelle de Paris 6 - University Courses on Svalbard (UNIS), Norvège 7 - Adam Mickiewicz University (AMU), Pozna, Pologne 1 2

1 - Question Since the end of the Little Ice Age, high latitude glacier margins have undergone net retreat in response to changing meteorological conditions, with associated geomorphological consequences. As a result, some parts of Spitsbergen are experiencing a transition from a landscape dominated by glacial and periglacial processes to one in which paraglacial landscape response is predominant, as other glacier margins all over the world. The aim of this programme is a better understanding of the impact of contemporary climatic change on the morphodynamic processes and plant dynamics.

The selected research field is constituted of the northwest Spitsbergen, Kongsfjorden area and surroundings, Svalbard.

2 – Paraglacial context In western part of Spitsbergen (Kongsfjorden, Krossfjorden, Isfjorden, Bellsund, Hornsund areas) cold-based valley glaciers have retreated 44

more than a kilometre from their Little Ice age maxima. Mass balance investigations on the local glaciers indicate a negative net balance, due to a decrease in winter snowfall and a concomitant increase in rainfall. So small glaciers (around 8 km2 in area) have been retreating throughout the 20th century, though in 1907 austre Lovénbreen, midre Lovénbreen and vestre Lovénbreen were at their maximum, with domed fronts associated to the outmost frontal moraines, as we can see on Isachsen’s photos. In 1936, these glaciers were still very close to their terminal moraines.

3 – Sediment fluxes and paraglacial progradation of the coastal zone One consequence of these changes in climate and glacier mass budget is that glacigenic sediments exposed by glacier retreat are being extensively reworked by proglacial meltwater streams. Active outwash plains occupy the zone between arcuate terminal

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

moraine complexes and fjord coastline which experiences local progradation where sediment input is augmented but local retreat where sediment input is reduced. The barrier coastline at the seaward end of the outwash plains constitutes a paraglacial coast in which the nearshore sediment budget is dominated by inputs of reworked glacigenic sediments transported by glacial meltwater streams.

Average shoreline progradation is estimated to amount to 3 m yr-1 over the last 30 years, a period of uninterrupted sediment provision from the glacial runoff system.

4 – Paraglacial modification of sedimentmantled slopes On the lateral moraine, like on the Colletthøgda or Conwaybreen, the active processes reworking sediments are debris flows. Process occurs each “summer” and is not dependent on extreme events but on the spatial distribution of ice inside the sedimentmantled. Rapid melting ice-core produced both slumping and translational sliding and transfers of saturated sediments generate small alluvial fans. Paraglacial dynamic modified slope profiles (reduction in gradient from a mean angle of 37° to 15°). Rapidly, full sequence of paraglacial slope modification (gully incision-stabilisation) may occur within few decades.

5 – Plant dynamics on glacier foreland Knowledge of the history of glacier retreat, it is possible to estimate rates of plant colonisation since the end of the little ice age.

In front of the ice margin, deglaciated since ten years, neither floristic groups nor plant cover but only moss (Polytricum species) can be seen. After 35 years of deglaciation, plant colonisation begins and floristic groups

are composed of 16 vascular plant species and covered 14 % on space. After 65 years of deglaciation, the floristic situation has evolved but the advance is less evident than during the preceding stages. However, surface reworking due to paraglacial processes takes place and constitute a hindrance to plant cover maturation.

6 – Weathering on glacier foreland On the other hand, we continue our investigation about rates of erosion of cold processes and weathering. We use Grant Squirell 1022 to have very precise thermic datas for erratic limestone. We use also a Schmidt hammer to know rates of weathering on slope and erratics that know paraglacial evolution since the end of glacial period. A SEM-study of the quartz surfaces has been investigated and micro-forms from glacial, fluvio-glacial, aeolian, frost, chemical and biological processes, are analysed.

Photo MEB ?

7 -Conclusions In western part of Spitsbergen, glaciers have retreated more than one kilometre from their Little Ice Age limits, all over the 20th century, and offer instructive examples to analyse paraglacial dynamics. Those examples show how polar environment answers after climatic change and how paraglacial dynamics succeed to glacial dynamics, in time and space, in geomorphological landscape evolution.

8 – Recent references ANDRÉ M.-F., 2003 - Do periglacial areas evolve under periglacial conditions ?

Geomorphology, 52, 149-164.

ETIENNE S., 2003 – L’apport de la microclimatologie à l’étude des processus 45

Shifting Lands. New insights into periglacial geomorphology

de météorisation. Résultats préliminaires au Spitsberg. Environnements périglaciaires, 28, p.66-72.

ETIENNE S. & ANDRÉ M.-F., 2003 — Variabilité de la hiérarchie des processus de météorisation dans divers milieux nordatlantiques (Islande, Labrador, Laponie, Spitsberg). Géomorphologie, 3, 177-189.

LAFFLY D. & MERCIER D., 2002 - Global change and paraglacial morphodynamic modification in Svalbard, International Journal of Remote Sensing, vol. 43, n°21, 4743-4760.

MERCIER D., 2003 - Glaciaire, paraglaciaire, périglaciaire : relais et combinaisons de processus, Bulletin de l’Association de Géographes Français, 4, 349-354.

MERCIER D., ÉTIENNE S., & SELLIER D., 2004 – Recent paraglacial slope deformation in the Kongsfjorden area, West Spitsbergen (Svalbard), in A.A. Beylich, S. Sæmundsson, A. Decaulne, O.

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Sandberg (ed.), First Science Meeting of the European Science Foundation ESF – Network SEDIFLUX, Náttúrustofa Nordurlands vestra, 3, 46-47.

MERCIER D. & LAFFLY D. - 2005 – Actual paraglacial progradation of the coastal zone in the Kongsfjorden area, West Spitsbergen (Svalbard), in Cryospheric Systems: Glaciers and Permafrost, Ch. Harris & J. Murton (eds), Special publication n°242, chapter X, Geological Society, Londres, 111-117.

MOREAU M., 2003 : La reconquête végétale des marges libérées des glaces depuis la fin du Petit Âge Glaciaire au Spitsberg.

Bulletin de l’Association de Géographes Français, 4, 377-385.

MOREAU M., MERCIER D. & LAFFLY D., 2004 – Un siècle de dynamiques paraglaciaires et végétales sur les marges du Midre Lovénbreen, Spitsberg nordoccidental, Géomorphologie, 2, 157-168.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Paraglacial and Weathering Poster Session

FORMATION AND DEFORMATION OF PERIGLACIAL DEPOSITS, CORNWALL, SW ENGLAND Jasper Knight Department of Geography University of Exeter in Cornwall Penryn, TR10 9EZ j.knight@exeter.ac.uk

Slope deposits composed of angular rock fragments (head) and formed under a periglacial climate are known throughout coastal south-west England where they are interbedded with raised beach, aeolian, fluvial and organic sediments (Scourse, 1985, 1996; Harrison, 2004). Radiometric dating indicates slope deposit formation during parts of the Middle to Late Pleistocene, but these dates are not meaningful where sediments have been continually reworked downslope and where lithostratigraphic members, identified on the basis of stratigraphic position, are correlated between geographically isolated rock-bounded embayments with different infilling histories.

An alternative method of identifying phases of slope activity is to consider superposition of periglacial structures within individual lithostratigraphic members irrespective of assumptions of age.This study describes evidence for several phases of slope and ground activity from head units (0.4-1.6 m thick) and associated sediments from four well-known sites on the coast of Cornwall (St Loy, Godrevy, Trebetherick, Towan) (Fig.1). Based on their stratigraphic position with respect to raised beach gravels, slope deposits at these sites are of different ages (Campbell et al., 1999) and therefore

reflect different climate trends (warming or cooling tendencies). These climate trends should be manifested as the superposition of different sedimentary structures which reflect periods of varying coldness and aridity. For example, at Trebetherick lens-shaped units of cryoturbated head overlie reddened aeolian sand in which sand wedges are developed. Wedges with cryoturbated breccia infills are also developed at the top of the head unit. Superposition of these features suggests a complex sequence of subaerial exposure, ground and wind-blow activity and desiccation. At Godrevy, the boundary between head and the underlying sand unit is deformed by cryoturbation and is marked by finger-shaped sand-filled cracks. Within the head unit, smaller clasts have been deformed around larger clasts, suggesting different levels of clast mobility based on their size. Large-scale cryoturbations (< 1.2 m wide) are also superimposed upon smaller cryoturbations at this site.

The presence of superimposed periglacial sediments and structures indicates multiple periods of land surface instability under different thermal and hydrological regimes throughout the Middle and Late Pleistocene.

This time period was therefore one of both dynamic climate change, and dynamic land 47

Shifting Lands. New insights into periglacial geomorphology

surface/active layer response to climate cooling and warming tendencies.

References Campbell, S., Hunt, C.O., Scourse, J.D., Keen, D.H. and Croot, D.G. 1999. Southwest England. In: Bowen, D.Q. (ed) A revised correlation of Quaternary deposits in the British Isles. Geological Society Special Report, 23. Geological Society, London, 66-78.

Harrison, S. 2004. South West England. In: Lewis, C.A. and Richards, A. (eds) The Glaciations of Wales. Logaston Press, Hereford, in press.

Scourse, J.D. 1985. Late Pleistocene stratigraphy of the Isles of Scilly and adjoining regions.

Unpublished PhD thesis, University of Cambridge.

Scourse, J.D. 1996. Late Pleistocene stratigraphy and palaeobotany of north and west Cornwall. Transactions of the Royal Geological Society of Cornwall, 22, 2-56.

Fig. 1. Location of sites investigated in Cornwall, SW England 48

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Paraglacial and Weathering Poster Session

THE INFLUENCE PROCESSES

OF

PERMAFROST

ON

PARAGLACIAL

Bernd Etzelm端ller Department of Geosciences Physical Geography University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo Norway

In arctic and mountain areas where glaciers and permafrost co-exist, the thermal regime of the ground and the glacier ice is interrelated. Is a glacier ending in a permafrost environment, at least marginal parts of the glacier are cold-based, favoring the build up of ice-cored moraines, which may persist over long timer periods. The poster illustrates hypothetically the consequences of glacier-permafrost interaction in the light of landform generation, erosion and particulate sediment transport pattern. In this respect, icecored moraines play an important role for the sediment evacuation of recently deglacierised catchments. The poster tries to show how permafrost in glacierised catchments reduces the variability of sediment yield and promotes sediment storage over longer time periods.

Sediment magazines in these areas are mobilized during permafrost degradation

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Shifting Lands. New insights into periglacial geomorphology

Paraglacial and Weathering Poster Session

PARAGLACIAL FANS IN THE MARITIME ALPS (WESTERN ALPS, ITALY): LANDFORMS, SEDIMENTS AND SIGNIFICANCE Nicola Casarosa, Paolo Roberto Federici, Marta Pappalardo, Adriano Ribolini Dipartimento di Scienze della Terra University of Pisa Via S. Maria 53 56126 Pisa, Italy

In the Maritime Alps, particularly in the mid-low part of Stura and Gesso basins, the retreat of the Pleistocene glaciers exposed the slopes to an accelerated geomorphic activity, involving so the thick and extended glacigenic sediments as the bare rockwalls. These were subjected to rock slope deformation and instability, namely deep-seated gravitational slope deformations and enhanced rockfall and talus accumulations. A strong adjustment of sediment-mantled slopes led to the formation of fan-shaped landforms infilling the valley bottoms. Morphometry and facies analyses were used to understand the processes that led to fans formation.

Fan gradients were calculated and related to area (A), height (Ht), length (Lb), relief number (N = Ht/(A)1/2) and mean slope (Ht/Lb) of the relative sediment-supplying basins. The results evidence that in many cases a correlation between source basins and fans morphometry does not exist (R2 = 0.1-0.2), suggesting a dependence of the fans shape mainly from the availability of debris in the source areas. The fans with 50

these morphometric characteristics were selected for a geomorphological survey and stratigraphic analysis.

Fan-head trenching, base level dissection and truncation (fan terraces) are the main post-depositional modifications of the fans surface. These erosional processes indicate a progressive reduction of sediment load through time, and a lowering of the valley floor base level after an aggradation phase. Moreover, the depositional process readjustment to the lowering base level led to the formation of small multilevel fans (telescopic structure) at the fan terraces base.

The stratigraphic characteristics observable in the vertical sections allow to group all the fans in two categories on the basis of the main depositional process: mass-flow dominated (gravity flow) fans and stream-flow dominated (fluvial) fans. Mass-flow dominated fans are made up by an alternance of a) coarse-sandy gravel deposits, well sorted, massive and clast supported (Gm2), and b) gravel deposits, poorly sorted, massive and matrix-supported (Gms), typical sequence of debris-flow events.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Stream-flow dominated fans show lithofacies with characteristics shifting from Gms to very coarse sandy-gravel deposits, massive and poorly sorted, clast-supported, moderately stratified, typical of sheetflood in more sediment-laden flow (Gm1).

The rock fragments lithology and shape indicate that most of the debris supply derives from a) the reworking of glacigenic sediment mantling the slopes, b) the rockwall instability processes (rock falls, talus slope accumulation) likely triggered by stress release and freezethaw cycling.

Fans morphometry and facies point out that this marginal alpine sector (only 40 km far from the Mediterranean Sea) underwent to a post-Last Glacial Maximum paraglacial evolution, when huge fans were built and infilled the valley bottoms. Debris flows proved to be the most active slope processes in this paraglacial landsystem, redistributing an high quantity of unconsolidated glacigenic sediment.

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Shifting Lands. New insights into periglacial geomorphology

Paraglacial and Weathering Poster Session

RESULTS AND CHALLENGES IN STUDYING PAST AND CURRENT VALLEY-TO-FJORD SEDIMENT TRANSPORT – THE SEDITRANS EXAMPLE FROM WESTERN NORWAY Knut Stalsberg, Eiliv Larsen Geological Survey of Norway N-7491 Trondheim Norway knut.stalsberg@ngu.no, eiliv.larsen@ngu.no

Valleys and fjords of Norway may be considered as conduit for sediment transport from the mountain areas to the continental shelf. Studying present sediment transport and accumulations in the different parts of the valley-fjord system makes it possible to reconstruct the evolving sediment filling in three dimensions from the present glacier, through the valley, and into the fjord. The main goals of the SEDITRANS project (2004 – 2007) are to identify sedimentary processes, determine the distribution of deposits, constructing qualitative and quantitative models, providing basic knowledge on erosion-, transport- and sedimentary processes of glaciated coastal regions. The study area form a transect from the present snout of the Jostedalsbreen glacier to the ice front position during the Younger Dryas maximum in Nordfjord, western Norway. This transect comprise well-defined subaquatic and subaerial depositional systems such as moraine ridges, fluvial plains, colluvial fans, deltas and lacustrine and marine troughs. Accordingly, our project is organized in sub-tasks focusing on the glacial, fluvial, gravitational, lacustrine, 52

and marine depositional systems, as well as the development of intergrated depositional models. The following field activities have been started.

1) The chemical composition of river waters will be used to estimate the dissolved load running out of the watershed and the order of magnitude of the present chemical denudation rate. The geochemical depletion of soils developed on known-ages tills will be used to estimate the long-term chemical denudation rates, and then compared to the long and short-term physical denudation and deposition rates.

2) Detailed DEM’s covering one of the glacier forefields and a series of marginal moraines are made from state-of-the-art land surveying data combined with automated digital photogrammetry. Although very important, this cannot be transformed directly to the volumes of eroded bedrock because evidently some of the material are polycyclic. This will be tried estimated through detailed process studies.

3) Different kinds of acoustic data were sampled within the marine sink area. Within

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

the fjord basin sediment thickness are normally 100-200 ms TWT (80-160 m). The largest volume of sediments appears close to the fjord head, where thicknesses exceed 200 ms TWT. The sediment succession constitutes mainly glaciomarine sediment from the last deglaciation and the Holocene (or â&#x20AC;&#x153;normal marineâ&#x20AC;?) sediment package is suggested to be maximum 15 ms TWT (12 m) thick.

4) A total of 3.5 km georadar profiles and 1.3 km of seismics have been acquired from one of the sub basins within the valley.

The combination of these two methods provides information on depth to bedrock and stratigraphic information at high resolution for the upper part of the valley fill. Good

GPR penetration down to 40 m allowed separation of some valley fill components, e.g. glaciofluvial sediments and slide deposits.

5) Existing maps cover part of the valley and show the quaternary deposits in general. A more specific characterisation of sediment genesis has started, and forms a first step in quantifying the contributions to the sediment budget from different processes. Colluvial deposits form well defined accumulations like fans, rock fall talus and rock avalanche deposits, and clearly show the primary transport agents. Debris flows and fluvial erosion act as secondary mechanisms, transporting sediments further down and into the valley fill.

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Shifting Lands. New insights into periglacial geomorphology

Paraglacial and Weathering Poster Session

PRESENTATION OF THE GEOMORPHOGLIS PROGRAM (POSTGLACIAL GEOMORPHIC DYNAMICS IN SOUTH-ICELAND, 2006-2009) Samuel Etienne, Virginie Comte, Morgane Priet-Mahéo, Erwan Roussel Université Blaise-Pascal Clermont-Ferrand II GEOLAB - CNRS UMR6042 Maison de la recherche 4 rue Ledru 63057 Clermont-Ferrand cedex 1 E-mail : setienne@seteun.net

Since the end of the Little Ice Age (around 1890 in Iceland), icecaps ang valley glaciers have receeded and new surfaces have been offered to geomomorphic and biogeographic processes. Paraglacial sequence seems very short but efficient in low-lying plains of south-Iceland where plant colonization might be very dynamic.

Reference Etienne S. 2004. Islande. Biogéomorphologie d’un milieu périglaciaire humide. Seteun, Clermont-Ferrand, 260 p.

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Paraglacial and Weathering Poster Session

WATER CHEMISTRY AND SOLUTE FLUXES IN THE KIDESJOKI CATCHMENT, SUBARCTIC FINNISH LAPLAND Achim A. Beylich1, Karl-Heinz Schmidt2 Geological Survey of Norway, N-7491 Trondheim, Norway; Achim.Beylich@ngu.no Institute of Geography, Martin-Luther-University Halle-Wittenberg, Halle/S., Germany

1 2

Water balance, water chemistry and solute fluxes have been investigated in the Kidesjoki catchment (16.1 km²; 150 - 365 m a.s.l.; 69°47`N, 27°05`E) in subarctic Finnish Lapland. The study area is part of the Precambrian Baltic Shield and is lithologically composed of gneisses and granulites. Discharge was measured at the outlets of selected subcatchments within the Kidesjoki catchment and at the outlet of the entire drainage basin. The pH values, TDS and ion composition of snow pack, precipitation and surface water were analysed on samples collected during the 2003 summer field season at several selected sites within the entire catchment area.

Chemical water analysis included the components Na+, K+, Mg2+, Ca2+, Cl-, F-, Brand SO42-. Fresh and (partly) weathered rock samples collected at bedrock outcrops within the catchment were analyzed for chemical components of relevance for the results from the surface water analyses. Water chemistry is clearly dominated by Na+, Ca2+, Cl- and SO42, and pH values of the surface water range normally from 6.3 to 6.5. Altogether, chemical

denudation appears to be low in this subarctic environment. Atmospheric solute inputs are estimated to be in the range of 5.1 t km-2yr–1, based on mean annual precipitation of 415 mm and TDSmean of 12.4 mg l-1, derived from snow pack samples and precipitation samples. The preliminarily calculated chemical denudation rate for the entire catchment is in the scale of 2.9 t km–2yr -1.

Spatio-temporal variability of solute yields and chemical denudation within the catchment is mainly caused by spatial variations of winter ground frost duration and regolith thicknesses. In spite of the low intensity of chemical weathering and the low solute concentrations in the surface water, chemical denudation appears to be more important than mechanical fluvial denudation and is obviously the most important denudative process type in this subarctic environment.

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Shifting Lands. New insights into periglacial geomorphology

Paraglacial and Weathering Poster Session

SOIL AND WEATHERING ON A GLACIAL FORELAND, STORBREEN, JOTUNHEIMEN, NORWAY Robert G. Darmody, Charles E. Allen, Colin E. Thorn University of Illinois Santa Cruz, CA University of Illinois

Chemical weathering and soil development were examined at Storbreen glacial foreland in Norway. We observed soil weathering at this â&#x20AC;&#x153;Little Ice Ageâ&#x20AC;? foreland on moraines dated to 1750, 1810, 1870, and 1928, and, in addition, on the adjacent 9000-year-old surface. An elevational range of 1165-1465 m was encompassed by the sample sites. All soils examined were weakly developed, only showing rudimentary podzolization. However, there were detectable physical, chemical, and mineralogical differences between the same age soils at different elevations and between the same elevation soils of differing ages. Finer textured soils were associated with older and higher elevation sites, possibly due to aeolian additions. Soils became more acidic, i.e. lower base saturation and pH, with time, and extractable Al and Fe, CEC, organic matter, and C: N ratio tended to increase with time, while most extractable elements generally decreased with time. Increased extractable Mg, Al, Fe, K, P, and Cu was related to higher elevation. The rate of organic N accumulation diminished from 0.120 to 0.001 g cm-2 yr1 on the 68 and 9000-year-old surfaces, 56

respectively. Organic C accumulation rate was greatest on the 248-year-old surface, 0.31 g cm-2 yr-1, and least on the 9000-year-old surface, 0.02 g cm-2 yr-1. Rates of organic C and N accumulation increased with elevation.

Primary minerals, quartz, mica, feldspar, and amphibole dominated mineralogy of the soils, but secondary minerals, in particular hydrobiotite, increased with age and elevation.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Permafrost Dynamics Session Oral Paper

INVESTIGATIONS ON PERMAFROST IN THE FRENCH ALPS: FIRST RESULTS AND FUTURE ORIENTATIONS Xavier Bodin Doctorant géomorphologie périglaciaire Université Paris 7 / Institut de Géographie Alpine 8 rue Etienne Marcel 38000 Grenoble Tel : 04 76 47 36 89

French Alps include a lot of massifs that reach and outgrow 3000 meters, and which may be underlain by permafrost in the upper part of their periglacial belt. Comparing with the neighbouring Swiss Alps, where permafrost is well known, monitored and spatially defined, it appears that French periglacial workers don’t have paid many attention to ‘their’ alpine permafrost.

Trying to partly fill the gap, some results of recent works on permafrost distribution in French Alps and future research orientations are presented. The main objectives of our research is to investigate the relationships between permafrost and climate through air temperature and ground surface measuring, to analyse the relative influences of the main parameters and to propose a model for predicting spatial distribution of mountain permafrost in the Combeynot massif (Hautes Alpes). It is a 30 km² mountainous massif, homogeneous in term of lithology (granite) and climatology and its elevations range from 2200 m to 3155m. Glaciers are quasi nonexistent and permafrost belt has a potential extension of 200-400 m. Within Combeynot

massif B. Francou has intensively investigated talus formation and evolution in the ‘Combe de Laurichard’.

In order to perform a correct analysis of the main factors controlling permafrost distribution, an approach based on multiscaled investigations and combination of descriptive empirical-based model and explanatory process-oriented model is chosen. Local study of the Laurichard rock glacier with ground temperature measurements provide knowledge about the importance of seasonal variation of heat transfer in ground thermal regime. Thanks to systematic BTS (Basal Temperature of winter Snow cover) measurements on a wide range of slopes, a topoclimatic model of the Combeynot massif is elaborated, allowing setting up of relatively accurate map of permafrost distribution simulation.

Several kind of data (air temperature, ground surface temperature and ground temperature measurements, geophysical investigation and remotely sensed data) allow comparison with the topoclimatic model, and consequently provide improvement of the understanding 57

Shifting Lands. New insights into periglacial geomorphology

of mountain permafrost occurrence.

Furthermore, the knowledge on ground thermal regime on Laurichard rock glacier can be interpreted in terms of permafrost creeping dynamic, thanks to measurements of shallow displacements rates on Laurichard rock glacier (monitored since more than 20 years) and geophysical soundings.

RÉSUMÉ Les Alpes françaises sont composées d’un grand nombre de massifs qui atteignent et dépassent les 3000 m d’altitude, laissant supposer que des portions non-négligeables peuvent être recouvertes de pergélisol.

Alors que le pergélisol des Alpes suisses est bien connu, suivi et spatialement défini, les chercheurs français sur le périglaciaire se sont peu intéressés au pergélisol présent en France.

Afin de combler en partie cette lacune, sont présentés ici les résultats de travaux récents sur la distribution du pergélisol en France et les orientations de recherche futures.

Les objectifs principaux de notre recherche consistent à étudier les relations entre le pergélisol et le climat au travers des mesures de température de l’air et du sol, à analyser les influences relatives des principaux paramètres et à proposer un modèle de distribution du pergélisol sur le massif du Combeynot. Ce dernier, d’une surface de 30 km², est homogène aux niveaux lithologique et climatique et est compris entre 2000 m et 3155 m d’altitude.

Les glaciers y sont quasiment inexistants et la frange à pergélisol potentielle s’étale sur 200 à 400 m de dénivelé. C’est dans ce massif que B. Francou a étudié les mécanismes de formation et d’évolution des éboulis, en particulier dans la Combe de Laurichard.

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Afin d’analyser correctement les principaux facteurs contrôlant la présence ou non de pergélisol, une approche basée sur des études à plusieurs échelles et une combinaison de modèles descriptifs et empiriques et de modèles explicatifs orientés sur les processus a été choisie. L’étude locale du glacier rocheux de Laurichard, avec les mesures de température du sol, fournit des informations sur l’importance des variations saisonnières des transferts de chaleur sur le régime thermique. Grâce à des mesures BTS (Basal Temperature of winter Snow cover, température à l’interface sol/neige) systématiques sur les versants du massif, un modèle topoclimatique du massif du Combeynot a été élaboré, permettant de simuler de manière relativement précise la distribution du pergélisol. Différents types de données (température de l’air, température à la surface du sol et dans le sol, sondages géophysiques et photo-interprétation) sont comparées au modèle topoclimatique et améliorent la compréhension des conditions favorables au pergélisol de montagne.

Enfin, les connaissances sur le régime thermique du glacier rocheux de Laurichard peuvent être interprétées en terme de dynamique de fluage du pergélisol, grâce au mesures de déplacement superficiel (effectuées depuis plus de 20 ans) et aux résultats des sondages géophysiques.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Permafrost Dynamics Session Oral Paper

MUD BOILS AND SOLUTE FLUXES IN PERIGLACIAL LANDSCAPES Julia Boike1, Kurt Roth2, Olaf Ippisch3, Birgit Hagedorn4 1. Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany 2. Institute for Environmental Physics, University of Heidelberg, Germany 3. The Centre for Interdisciplinary Scientific Computing, University of Heidelberg, Germany 4. University of Washington, Quaternary Research Center, Seattle, WA, USA

What role do frost boils play in transport and storage of solute fluxes in a permafrost environment?

The seasonal and spatial behaviour of solute concentration within one mud boil is analyzed to classify these landscapes as potential solute accumulators or leachates.

Mud boils, a form of non sorted circles, cover the surface in many periglacial landscapes.The vegetation covered rim acts as an effective buffer to the downward movement of water and chemicals, while the bare center experiences larger fluxes of heat and mass.

Since dissolved chemicals affect the electrical conductivity of water (ECw), measurements of bulk soil electrical conductivity (ECb) offer potential for estimating solution concentration. ECb is measured automatically hourly using 32 time domain reflectometry probes over an approximate 1x1 m mud boil close to Ny-Alesund, Spitsbergen, since 1998.

ECw is calculated from ECb measurements using the model of Boike and Roth (1997) requiring only water content.

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Shifting Lands. New insights into periglacial geomorphology

Permafrost Dynamics Session Oral Paper

REMOTE SENSING AND CLASSIFICATION OF THERMOKARST STRUCTURES FORMED DURING HOLOCENE CLIMATE CHANGES IN THE LAPTEV SEA COASTAL REGION, NE ARCTIC SIBERIA G. Grosse*, L. Schirrmeister*, H.-W. Hubberten*, Ch. Siegert*, V.V. Kunitsky째 * Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, Germany 째 Permafrost Institute Yakutsk, Russian Academy of Science, Yakutia

Periglacial surface structures are indicators for certain stages of landscape development and for regional climatic developments in the Siberian Arctic. The use of satellite data is very efficient for the characterisation of the periglacial relief, as morphological structures, like thermokarst depressions, are easy to identify by remote sensing in Arctic tundra areas with low vegetation.

The NE Siberian Arctic periglacial lowlands along the Laptev Sea coast are characterized by a sedimentary environment, which is affected by strong changes during the Holocene. Large regions consist of ice super-saturated permafrost deposits of the so-called Ice Complex. The Ice Complex is a mostly fine-grained paleo-soil sequence with high amounts of segregated ice (up to 160 % compared to dry mass) and big ice wedges (some meters in width and several 10 meters in depth). In these permafrost deposits extensive subsidence occurred during the Holocene warming due to ground ice thawing and a thermokarst relief has formed. In many regions the thawing is still in progress.

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High-resolution, panchromatic CORONAsatellite images in combination with mediumresolution, multi-spectral Landsat-7 ETM+ data, topographic and thematic maps and field data allow the characterisation and classification of different structures in exemplarily studied areas of the Laptev Sea coastal lowlands (Bykovsky Peninsula, Mamontovy Klyk, New Siberian Islands). The different data are merged in a Geographical Information System (GIS) to enhance datahandling and information output.

The remotely sensed features of structures like initial thermokarst ponds, thermokarst lakes, thermokarst depressions, lagoons, thermo-erosional valleys, thermo-erosional ravines and pingos are described in detail and conclusions for Holocene landscape evolution are drawn from spatial distribution and development stage in the coastal lowland.

Keywords: Thermokarst, Remote sensing, Northeast Siberia, Holocene, Climate change

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Periglacial Dynamics Session Oral Paper

PERIGLACIAL GEOSYSTEM CHANGE: EVENT VERSUS TREND DYNAMICS Martin Gude Department of Geography University of Jena LĂśbdergraben 32 D-07743 Jena Germany E-mail: martin.gude@uni-jena.de

Geomorphic dynamics in periglacial landscapes are characterized by a variety of processes. These act either as more continuous (e.g. solifluction) or as event-like processes (e.g. debris flows). Not only for periglacial geomorphology the relation of these process types concerning sediment budgets, landscape denudation and predominance of forms is widely discussed.

Basically, events and trends with their mass transfer rates can be defined as the principal procedures of geomorphic dynamics. Events are characterised by an abrupt but short term change of mass transfer rates. In contrast, trends reflect long lasting mean changes in the transfer rates. Consequently, any change can be described as an event, a trend, or a combination of both.

The assessment of this topic in field studies is characterized by problems in data acquisition methods, which typically escalate with increasing magnitude and decreasing frequency of events under surveillance.

Improvements of field methods in recent

years, both for observation and measurement of event-like mass transfer processes and for investigation of correlated sediments, have enhanced the possibilities for comparative studies of sediment budgets. Especially geophysical methods and datalogger and sensor techniques face an increasing usage in this context.

By means of results from investigations in two periglacial catchments, the Liefdefjord in NW-Svalbard and the Kärkevagge in NSweden, applications of these field methods are demonstrated. The studies allow for a comparative analysis of sediment transfer rates in a variety of time scales and process types. The findings stress the importance of event-like processes in landscape evolution.

Especially for a fluvial environment in NW-Svalbard, the broad span of sediment transport magnitudes and frequencies are reconstructed. While floods account for a denudation of 40 t km-2 a-1 on the average, slushflows cause a denudation rate of approximately 20 t km-2 a-1. But not only the 61

Shifting Lands. New insights into periglacial geomorphology

denudation rate is significantly altered by the slushflows, they at the same time represent formative events concerning landscape sculpturing.

Gude, M. & Scherer, D. (1999): Atmospheric triggering and geomorphic significance of fluvial events in high-latitude regions.

- In: Crozier, M. & M채usbacher, R. (eds.): Magnitude and frequency of geomorphological processes, Z. Geomorph.

N. F. Suppl.-Bd. 115: 87-111.

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Periglacial Dynamics Session Oral Paper

THE INFLUENCE OF GEOLOGICAL CONDITIONS ON THE DISTRIBUTION OF ROCK GLACIERS - NIEDERE TAUERN MOUNTAIN RANGE, STYRIA, AUSTRIA Kellerer-Pirklbauer Andreas1, Avian Michael2, Lieb Gerhard Karl2, Proske Herwig1 1 2

JOANNEUM Research, Graz, Austria Institute for Geography and Regional Sciences, University of Graz, Austria

Geological conditions are of crucial importance for the formation of rock glaciers.

In this study the lithological conditions of the debris source area (mostly headwalls) of 332 intact and relict rock glaciers of the Niedere Tauern Mountain Range (Styria, Austria) have been examined and analysed.

First results are shown here. The spatial distribution of the 332 rock glaciers is based on preworks. Lithological determination is based on an official geological map at scale 1:200,000. In most cases more than one type of lithology can be found in the debris source area of a given rock glacier. This fact has to be considered. Hence, three different classes of relevance have been distinguished: lithology that covers 50 to 100% (GM200-a), 25 to 50% (GM200-b) and 0 to 25% (GM200-c) of the total debris source area (fig. 1). In terms of number of different lithologies per rock glacier 76 out of 332 rock glaciers feature only one, 155 two and 101 three lithologies.

The class GM200-a (n=332) is dominated by the four lithologies (91.9%), which include mica schist (44.3%), paragneiss (20.5%), orthogneiss (14.8%) and slate (12.3%). Of

minor importance for the class GM200-a are amphibolite, quartzite, hornblende gneiss (1.8% each), marble (1.5%) and limestone (0.3%). For the class GM200-b (n=256) the situation is different. By far the most important lithology is morainic material (40.6%). In terms of solid rock lithologies amphibolite (21.9%) and paragneiss (10.2%) are significant.

A portion of ~5% each are covered by mica schist, orthogneiss, granite-gneiss and marble.

For the third class â&#x20AC;&#x201C; GM200-c (n=101) - the situation is again very different. Out of 101 rock glaciers with three different lithologies the major portion consists of moraines (73.3%).

Only 5 solid rock types are significant in this class: marble (6.9%), paragneiss (4.0%), and orthogneiss, slate and black mica schist (3.0% each).

This quantitative analysis of 332 rock glaciers clearly demonstrates the great importance of a number of metamorphic rock types on the formation of rock glaciers. These relevant rock types are mica schist, paragneiss, orthogneiss, slate, amphibolite, granite-gneiss and marble.

Furthermore, morainic material seems to play a crucial role in the formation of rock glaciers 63

Shifting Lands. New insights into periglacial geomorphology

within the study area as well. This surprising fact is mainly due to the used geological source map: (a) areas covered by moraines are displayed generously and (b) areas covered by rock glaciers in the field have not been recognised as such in the used map.

Figure 1: Lithological conditions of 332 rock glaciers in the Niedere Tauern Mountain Range (Styria, Austria); explanation of lithological abbreviations: MS mica schist, PG paragneiss, OG orthogneiss, SL slate, AM amphibolite, QU quartzite, HG hornblende gneiss, GG granitegneiss, MA marble, LS limestone, BM black mica schist, AG augen gneiss, MO moraine

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Periglacial Dynamics Session Oral Paper

MORPHOGENETIC PHASES OF ROCK GLACIER IN THE HIGH MOUNTAIN OF ARAGONESE PYRENEES. Enrique Serrano1, Carlos Agudo2 1 2

Department of Geography. University of Valladolid.

Edelvives, Madrid.

The aragonese Pyrenees include the southern side of central Pyrenees with the highest massif of the Pyrenees (see fig 1).The high mountain is characterised by the presence of rock glaciers. Today is possible differenciate between active rock glaciers and relict rock glaciers. The last ones are the most common periglacial feature above 2.200 m a.s.l. We have studied the morphological, morphogenetic and morphodynamic characteristic of 87 rock glaciers of the Aragonese Pyrenees. The spatial distribution of relict and active rock glaciers, the morphostratigraphic relations with glaciomorphological features, the wall denudation estimation and the displacement velocity estimation of active rock glacier are used to stablish the different morphogenetic phases of rock glacier genesis.

The Tardiglacial and Holocene periods, included the Little Ice Age, are the main phases of genesis of rock glaciers. The rock glaciers are related to four morphogenetic phases, named: Inner advance maximun phase, Inner retreat phase, the Holocene deglaciation period, and Smaller advance. It is not possible to atribute the pyrenean rock glaciers either to one phase (the named Rock Glaciers Phase) nor to one time period (Tardiglacial). The rock glaciers of the Pyrenees have been generated in a periglacial environment narrow related to the glacial retreat and the continuous environmental changes on the high mountain from Latepleistocene to today.

Figure 1. Location of study area 65

Shifting Lands. New insights into periglacial geomorphology

Periglacial Dynamics Session Oral Paper

GROUND SURFACE TEMPERATURE IN SCREE SLOPES OF HIGH LATITUDE: CASE STUDIES IN THE VALAIS ALPS. Christophe Lambiel Institut de Géographie Université de Lausanne BFSH 2 CH-1015 Lausanne E-mail : christophe.lambiel@rect.unil.ch

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Periglacial Dynamics Session Oral Paper

PERIGLACIAL MORPHODYNAMIC AND ENVIRONMENT IN THE CENTRAL MASSIF OF PICOS DE EUROPA, CANTABRIAN RANGE, NORTH SPAIN. J.J. González-Trueba 1, E. Serrano 2 1 2

Dpt. Geography, University of Cantabria.

Dpt. Geography, University of Valladolid.

The Central Massif of the Picos de Europa accomadates the highest altitudes of the Cantabrian Range (Torre Cerredo 2.648 m.s.l., Torre del Llambrión 2.642 m.s.l.). Its altitude and its proximity to the Cantabrian Coast produce a particular climatic and environmental conditions that define the massif as a wet and deglaciated high mountain environment. In the Central Massif of Picos de Europa the periglacial environment is predominant up to 1.900 m a.s.l. It is the inferior limit of the high mountain belt.

The periglacial environment of the Central Massif of Picos de Europa have been defined related to landforms and processes.

Geomorphological maps, scale 1:25.000 and scale 1:10.000, were used as a inventory of active, inactive and relict landforms, and to identify landform associations and active processes. Furthermore botton temperature of winter snow (B.T.S.) measurements and ground measurements (UTL-1) have been made to observe the ground thermal regime and the winter evolution and distribution of the nival layer.

There are at least fourteen morphogenetic processes intervening, associated to gravity, solifluction, nivation (nival karst) and gelifluction. All of them form a fast system

of debris transference, in a very active morphodynamic system. This processes are organized in altitude. Debris talus and cones, ridges, nival karst and surface weathering are the most common features of periglacial processes. Nivation processes are common, but they are weak indicators of periglacial environments and they are not associated to either permafrost nor frost action. In the Central Massif of Picos de Europa it is possible to differenciate two morphoclimatic belts: 1º) Nivoperiglacial belt (between 1.900 – 2.300 m.s.l.), where nivation together with karstification processes and landforms are predominant. 2º) Cryonival belt (above 2.300 m.s.l.), with an intense gelifraction and presence of gelifluction and cryoturbation processes and landforms There are not conditions for the existence of continuous or discontinuous permafrost.

The Picos de Europa is characterized by a nivoperiglacial morphodynamic system, with some strictly periglacial conditions, limited to those areas that have been occuped by ice during the Little Ice Age. The massif has a big variety of actives morphogenetic processes and landforms sensitives to the current environmental changes.

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Shifting Lands. New insights into periglacial geomorphology

Periglacial Dynamics Session Oral Paper

LABORATORY SIMULATION OF SCARP DEGRADATION UNDER FREEZE/THAW CYCLES Marianne Font, Jean-Louis Lagarde, Daniel Amorese, Jean-Pierre Coutard, Jean-Claude Ozouf, Gérard Guillemet UMR CNRS 6143 “M2C”, Morphodynamique Continentale et Côtière, 2-4, rue des Tilleuls, 14 032 Caen, France.

E-mail : marianne.font@geos.unicaen.fr Tel : 33 (0)2.31.56.57.57 Fax : 02.31.56.57.57

The conjugate effects of tectonic and climatic processes have influenced landforms in intraplate zones, during Quaternary time. In Western France, evidences of scarp erosion under moist periglacial conditions can be found along the La Hague-Jobourg Fault Zone (North Cotentin, Normandy). In this area, cryoclastic processes, linked to periglacial conditions, have contributed to the cracking of rocks near the surface ; then sliding of cryoclasts during thawing periods gives rise to slope deposits several ten of meters thick.

Downward displacement of the cryoclastic material occurs mainly by cryoreptation, gelifluxion and debris flows.

A laboratory simulation of scarp degradation under periglacial conditions was carried out in a climatic chamber where temperature (freeze/thaw cycles), precipitations, and lithology (heterogeneous cryoclasts) were controlled. The evolution of the scarp morphology has been followed.

Laboratory simulation improves our knowledge of landform degradation that results from cryoclastic processes : – Slope processes involve (i) cryoreptation of the whole deposits (~ 0.3 cm of displacement by cycle), (ii) debris flows 68

which lead to prograded fan accumulation at the base of the slope, (iii) small mass slips ; – Landform evolution is characterised by (i) development of concave scarp profiles, (ii) scarp ablation as a consequence of debris flows and (iii) final slope softening ; – Erosional products at the base of the scarp indicate (i) falls against the scarp, (ii) fine-grained sole resulting from runoff, (iii) fans and flows of coarse material on the fine-grained material, (iv) stratified deposits when the slope decreases.

Quantification of the displaced material volume, along the experimental scarp, leads 3 2 to values about 1 cm /cm for 41 freeze/thaw cycles. Computations of the volume of rock eroded from the La Hague-Jobourg scarp by fitting digital elevation model data and field data, indicate heavy ablation rates about 5 m3/ m2 by climatic cycle.

Laboratory simulation demonstrates that scarps are particularly concerned by the climatic degradation in periglacial environments. Cryoclastic processes lead to significant ablation rates that can partially conceal the morphological signature of the Plio-Quaternary deformation in Normandy.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Periglacial Dynamics Session Oral Paper

THE ROLE OF HOLLOW SYSTEMS IN THE MODERN SEDIMENT BALANCE OF CULTIVATED WATERSHEDS (THE FOREST-STEPPE ZONE OF CENTRAL RUSSIA) V. Golosov, Nadezda Ivanova Moscow State University

Our investigations within different regions of the forest-steppe zone revealed that the hollow network represents the most effective pathway linking ploughed slopes and bottoms of the small valleys. The predominance of the sediment mobilization, transport or accumulation in different parts along the talweg of the hollow depends mainly on the morphometric parameters, particularly on the form of the longitudinal profile of the hollow.

Such significant role of the hollow network in the actual dynamic of the relief of agricultural regions determines the importance of the problem of its genesis. Apparently the hollows of ploughed slopes can be subdivided into two groups which differ in its genesis. The linear hollows without tributaries, the talweg of which coincides of the general slope gradient are usually formed by man-made erosion.

There are the depressions which originally represented the ploughing furrows or former field borders (after the abolishing reform in 1861 the new land shares were cut along the slope), transformed by erosion processes. The more complex and forked hollow systems are most likely the polygenic forms.

According to one of the supposition the part

of the actual hollows inherits the interblock depressions of the relict cryogenic polygonal relief. It was established that the zone of the widespread relict cryogenic morphosculpture reached in the Late Pleistocene to 48-49o N, i.e. more south that the actual south boundary of the forest-steppe zone.

RÔLE DES SYSTÈMES DE DÉPRESSIONS LINÉAIRES DANS LE BILAN SÉDIMENTAIRE MODERNE DES BASSINS VERSANTS CULTIVÉS (ZONE DES FORÊTSSTEPPES DE LA RUSSIE CENTRALE)

Nos recherches dans les différentes régions de la zone des forêts-steppes ont montré que le réseau des dépressions linéaires représente la voie la plus efficace reliant les versants labourés et le fond des petites vallées. La prédominance de la mobilisation, du transport ou de l’accumulation des sédiments érodés dans les différentes parties du talweg de la dépression linéaire dépend essentiellement des paramètres morphométriques, le plus souvent de la forme du profil longitudinal de la dépression.

Le rôle tellement considérable du réseau de dépressions linéaires dans une dynamique actuelle du relief des régions agricoles 69

Shifting Lands. New insights into periglacial geomorphology

détermine une importance d’un problème de sa genèse. Evidemment les dépressions linéaires des versants cultivés peuvent être subdivisées en deux groupes selon leur genèse.

Les dépressions linéaires sans affluents, avec le talweg coïncident le gradient principal d’un versant sont formées le plus souvent par l’érosion anthropique. Initialement c’était les sillons résultant de labour ou les anciennes limites des champs (après la reforme de l’abolition du servage en 1861 les nouvelles parcelles de terrain ont été installées le long de versants), transformes ultérieurement par les processus de l’érosion. Les systèmes plus compliques et bifurques sont probablement les formes polygénique.

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D’après l’une des suppositions, une partie des dépressions linéaires existantes aujourd’hui hérite les dépressions entre les blocs polygonaux de l’ancien relief cryogénique.

On a constate que la région d’une large propagation de l’ancienne morphosculpture cryogénique du Haut Pléistocène s’étendait jusqu’aux 48-49° de la latitude nord soit plus au sud que la frontière méridionale de la zone des forêts-steppe d’aujourd’hui.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Periglacial Dynamics Session Oral Paper

RELICS OF PERIGLACIAL PROCESSES IN MODERN RELIEF, SOIL COVER AND SURFACE GEOLOGY OF CENTRAL RUSSIAN PLAIN Vladimir Belyaev Moscow State University

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Shifting Lands. New insights into periglacial geomorphology

Periglacial Dynamics Session Oral Paper

ROCKS, GLACIAL HISTORY AND PERIGLACIAL LANDSCAPES OF THE SUDETES, CENTRAL EUROPE Piotr Migon, Andrzej Traczyk Department of Geography and Regional Development University of Wroclaw pl. Uniwersytecki 1 50-137 Wroclaw, Poland migon@geogr.uni.wroc.pl traczyk@uni.wroc.pl

The Sudetes Mountains host a variety of medium- and small-scale relief features, commonly considered as reflecting periglacial legacy in the present-day landscape.

These include blockfields, blockstreams and blockslopes, tors, rock-cut steps and cryoplanation terraces, rock glaciers, patterned ground, solifluction landforms and deposits. Spatial distribution of these landforms indicates two principal controls on the dynamics of Pleistocene periglacial environment: lithology and time.

The role of bedrock is reflected in different associations of cold climate landforms being supported by different lithologies. Rock glaciers, blockfields and blockstreams develop on massive, well-jointed rocks such as gabbro, fine-grained granite or basalt. Stepped slopes, rock cliffs, patterned ground and heterogenic solifluction mantles are typical for most metamorphic rocks. No distinctive landforms occur in mudstones, marls, shales and some sandstones, which all break down preferentially through microgelivation, or coarse granite subjected to granular disintegration. The occurrence of periglacial landforms and deposits is thus controlled by the characteristics of regolith, which in turn 72

shows different susceptibility to frost sorting, heave and development of ground ice.

The other control is time. Less elevated parts of the Sudetes were overridden by continental ice sheets in the Pleistocene, although a number of hills acted as nunataks.

Inventories of periglacial landforms in the areas within and outside the limit of inland glaciation differ qualitatively from each other, the former being relatively undeveloped. For instance, stepped slopes, tors and blockfields are virtually absent in the area covered by ice sheets. Nunataks in particular show clear trimlines, which are evidently older than OIS 2, and probably older than OIS 6. This suggests that periglacial geomorphology of the Sudetes is the cumulative effect of many successive cold periods during the Pleistocene and the timescales involved in the origin of periglacial landscapes are much longer than previously assumed for this area.

The observations from the Sudetes show limited applicability of uniform models of periglacial landform development in areas of diversified geology and Quaternary history, highlighting the role of lithology, structure and temporal constraints instead.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Periglacial Dynamics Session Oral Paper

THE RELATION BETWEEN RETROGRESSIVE THAW SLUMPS POLYCYCLIC PATTERN AND SHORELINE EVOLUTION ON HERSCHEL ISLAND,YUKON TERRITORY. Hugues Lantuit, W.H. Pollard Department of Geography, Burnside Hall McGill University 805 Sherbrooke Street West Montréal, QC H3A 2K6 - Canada

Herschel Island, also known as Qikiqtaruk, is located in the Beaufort Sea at 69°36’N, 139°O4’W on the northern coast of the Yukon Territory, Canada. The island is a moraine resulting from the late fluctuations of the Pleistocene ice sheets and is composed of marine, non-marine and mixed origin sediments (Bouchard, 1974).

The tremendous coastal retreat occurring in the area, which is assumed to be the most icerich area of the Canadian Arctic (Pollard and French, 1980) has been recently emphasized in the scientific community. Horizontal coastal retreat rates have been documented on Herschel Island for two different periods.

MacDonald and Lewis (1973) investigated coastal evolution on the Yukon Coastal Plain for the period 1954-1970 and reported an average horizontal coastal retreat rate of 0.68 m/yr. For the 1970-2000 period, Lantuit and Pollard (2003) documented an average coastal retreat rate reaching 1.03 m/yr.

Coastal erosion was shown to be important (>1m/yr) in the vicinity of large retrogressive thaw slumps (Lantuit and Pollard, 2003), in other words, where the shoreface exhibited high ice contents. Although horizontal retreat rates provide valuable information

about the amount of sediment released by coastal erosion, Hequette and Barnes (1990) have shown that there can be a discrepancy between horizontal and volumetric rates. The goal of this study was therefore to compare horizontal and volumetric coastal retreat rates, and to highlight the parallel evolution of these two datasets during the last half of the twentieth century.

Softcopy photogrammetric tools and fieldcollected GPS control points were used to compile a recent IKONOS stereo-pair and airphoto archives of Herschel Island from 1954 and 1970. Layers were then subtracted in ArcGIS to describe volumetric erosion.

Two major processes were outlined by the output layers. First, a direct observation of the coastal delineation confirmed a general correlation between volumetric and horizontal coastal retreat. Second, the sections of the coast associated to the greatest rates of volumetric erosion during the period corresponded to retrogressive thaw slumps characterized by intense polycyclic activity.

Retrogressive thaw slumps are landforms associated with the meltout of bodies of massive ground ice. They are commonly found along ice-rich coasts (Wolfe et al., 73

Shifting Lands. New insights into periglacial geomorphology

2001) and are often complex combinations of several scale-variable slumps. These slumps were easily idenditified by their bowl-shaped signature on the GIS layer.

The current study confirms that the greatest volumetric losses are also associated with these features and pinpoints that the polycyclic evolution of these landforms is reflected on the shoreline’s retreat pattern.

References BOUCHARD, M., 1974. Géologie des dépots meubles de l’île Herschel, Territoire du Yukon. M.Sc. Thesis, Montréal, Quebec, 70 pp.

HEQUETTE, A. and BARNES, P.W., 1990.

“Coastal retreat and shoreface profile variations in the Canadian Beaufort Sea.” Marine Geology, 91, 113-132.

LANTUIT, H. and POLLARD, W.H., 2003.

“Remotely sensed evidence of enhanced erosion during the 20th Century on Herschel Island, Yukon Territory.” Pp 54-59 in Rachold, V.; Brown, J.; Solomon, S.; Sollid, J.L. (Eds.): Arctic coastal dynamics: report of the 3rd International Workshop University of Oslo (Norway) 25 December 2002. Berichte zur Polar- und Meeresforschung, 443. Alfred-WegenerInstitut für Polar- und Meeresforschung: Bremerhaven, Germany.

MCDONALD, B.C. and LEWIS, C.P., 1973.

Geomorphic and Sedimentologic Processes of Rivers and Coast, Yukon Coastal Plain.

Geological survey of Canada.

POLLARD, W.H. and FRENCH, H.M., 1980. „A first approximation of the volume of ground ice, Richards Island, Pleistocene Mackenzie Delta, N.W.T.“ Canadian Geotechnical Journal, 17, 509-516.

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WOLFE, S.A.; KOTLER, E.; and DALLIMORE, S.R., 2001. “Surficial characteristics and the distribution of thaw landforms (1970 to 1999), Shingle Point to Kay Point, Yukon Territory.”

Geological Survey of Canada, Open File 4088.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Paraglacial and Periglacial Dynamics Poster Session

THE RELATIONSHIP BETWEEN KINEMATICS AND GEOMORPHOLOGY OF AN ACTIVE ROCKGLACIER, HINTERES LANGTALKAR, HOHE TAUERN, AUSTRIA Avian Michael1, Kellerer-Pirklbauer Andreas2 1 2

Institute for Geography and Regional Sciences, University of Graz, Austria, m_avian@sbox.tugraz.at Joanneum Research, Graz, Austria, andreas.kellerer@joanneum.at

The rockglacier Hinteres Langtalkar (Gössnitztal, Hohe Tauern, Austria) is featured with a complex morphology. The highest creeping rates of all measured rockglaciers in the Hohe Tauern range create distinctive furrows and ridges. Geomorphological as well as hydrological analyses were carried out within the last 10 years, so consequent observation of surface deformation was the logical next step. The rockglacier is embedded in a typical glacial lateral valley ending in an altitude of 2480m, has a length of appr.

600m and a width of 300m. Five observation periods were taken into account: 1969-1991, 1969-1974, 1991–1997, 1997–1998 and 1974–1998 (mass balance).

Especially the front of the rockglacier has been changing its appearance dramatically since 1991. Intensified dynamic resolved the solid structure, first evidences occured as early as 1994. Shifting of material and typical imbrication of the surface as well as a high amount of superficial fine grain is visible.

Numerous boulders dominate the forefield.

The reason for this outstanding event has still

to be elucidated, exceeding tensile stresses on a prominent headwall might be an explanation.

Area 1 remained inert until 1991, afterwards creeping rates increased outstandingly. A prominent transversal crevasse (1) determines a clear boundary of activity, further crevasses have been developing. Area 2 showed a constant behaviour with flow velocities up to 270 cm a-1 (1997-1998), creeping rates decreased homogeneously towards the root zones. Another extending transverse crevasse (2) divides active and comparable inactive zones, the surface below the crevasse has a constant loss of mass. The most inert part of the rockglacier is area 3 which surprisingly shows a distinctive structure most probably representing older stages of activity. In the upper part of the rockglacier two lateral moraines from 1850 and typical depressions are developed. The two root zones are identical with the area of the former cirque glacier which disappeared 30 years ago.

The entire rockglaciers has a significant negative mass balance of –45000 m³, corresponding to an average falling of surface 75

Shifting Lands. New insights into periglacial geomorphology

of 1,2 cm a-1 (1974-1998). Consequently the rockglacier is not only thinned out due to creeping processes but also shows a striking loss of substance.

Figure 1: Classification of rockglacier Hinteres Langtalkar in terms of surface deformation

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Paraglacial and Periglacial Dynamics Poster Session

MAPPING OF AN UNUSUAL ICE-CORED ROCKGLACIER, IN THE MONT THABOR AREA (NORTHERN FRENCH ALPS), LINKED TO THE DEGLACIATION SINCE THE LITTLE ICE AGE. Sébastien Monnier UMR 85-91 CNRS / Université Paris 1, Laboratoire de Géographie Physique EA 435 / Université Paris Val-de-Marne

The Mont Thabor rockglacier is located in the Arc valley, Northern French Alps, and is part of a 150 rockglaciers population recognized in and around the Vanoise Massif.

This rockglacier develops in a large cirque, at the foot of the quartzitic crags of the Mont Thabor (3178 m) ; its front lies at an altitude of 2650 m a.s.l. This is a large rockglacier (of 900 m. long), entirely consisting of quartiztic debris, where were observed many and spectacular massive ice exposures in the very warm 2003 summer, when all the firns on the surface disappeared. The ice was supposed to be relict glacier ice. At first sight, the Mont Thabor rockglacier shows a surface morphology analoguous to the so-called « porridge-like » morphology, typical of rockglaciers, with its ridges and furrows. But a detailled study of its morphology highlights more complex and original patterns. We have thus realized a large-scale mapping of the whole rockglacier and interpretation shows that many of the surface forms are linked to the melting of a buried glacier ice. From these observations, we propose a model of

the genesis of the Mont Thabor rockglacier morphology, linked to the deglaciation of the area. The latter was studied by the means of ancient maps and completed with field investigations, thus in a short-term interval, in this case since the Little Ice Age. In this age, the Mont Thabor glacier seemed to occupy a considerable area. We are finally led to the conclusion that this large and particular rockglacier, of glacial origin, has developed in the landscape during the two last centuries.

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Permafrost and Periglacial Dynamics Poster Session

SMALL SCALE INITIAL THERMOKARST IN THE REGION OF CAPE MAMMOTH TUSK (NORTHERN MIDDLE SIBERIA) V.V. Kunitsky, L. Schirrmeister *, H. Meyer *, G. Grosse * Melnikov Permafrost Institute, Russian Academy of Science, Russia * Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, Germany

Various sizes of thermokarst depressions form the Edoma surface (hummocky plain with thermokarst hills and ice-rich permafrost deposits of the Ice Complex) at the northern slope of the Pronchiishchev Range in arctic middle Siberia. The authors studied some of these depressions and their deposits during the Russian-German expedition “LenaAnabar 2003” in the area of Cape Mammoth Tusk (western Laptev Sea coast; 76.6°N, 117.2°E) during the summer of 2003.

Peaty patches around 10 to 50 m in diameter are frequently exposed at the 25 to 30 m high coastal cliff at the top of the Edoma. The outcrops show that depressions of about 1

78

m depth at the top of Edoma were totally filled by peaty loam (see photo). Such packets discordantly cover the Ice Complex deposits that compose the largest part of the Laptev Sea coastal section. The fillings of these small thermokarst depressions contain thin white ice wedges of Holocene age. The ice-banded and lens-like cryostructure and absolute ice contents of 50 to 60 weight % reflect moisture excess and a thin active layer during accumulation. Therefore, the boundary between the Ice Complex and the newly-formed deposits is situated at the base of the seasonal active layer.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

According to these observations, it was possible to separate a special variety of permafrost deposit, which is probably associated with the formation of small thermokarst depressions, the so-called â&#x20AC;&#x153;Bylaryâ&#x20AC;?, and is interpreted as initial thermokarst. In contrast to alas deposits, which were often associated with taliks, the described sediments were formed without taliks possibly at the base of small thermokarst depressions. Sometimes, small thermokarst depressions were transformed into alas depressions. Generally, the formation of several small-scale initial thermokarst depressions, as well as its peaty deposits, ends after drainage by linear-oriented erosion.

The formation and infilling of the small thermokarst depressions at the top of Edoma reflects special modern periglacial surface processes in the arctic Siberian lowlands. More detailed information of this phenomenon with cryolithological characteristics of the corresponding deposits will be presented in the poster.

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Shifting Lands. New insights into periglacial geomorphology

Permafrost and Periglacial Dynamics Poster Session

SLUSH FLOWS IN NORTH-WESTERN ICELAND AND THEIR GEOMORPHOLOGICAL IMPACT – THE CASE STUDY OF BÍLDUDALUR Armelle Decaulne1, Þorsteinn Sæmundsson² Physical Geography Laboratory UMR 6042 CNRS, GEOLAB, Maison de la Recherche , 4 rue Ledru, 63057 Clermont-Ferrand, France ² Natural Research Center of North-western Iceland, Aðalgata 2, IS-550 Sauðárkrókur, Iceland 1

Slush flows in Iceland seem rather rare, but they represent 9% of recorded snow avalanches in the northwestern part of the country. This is the consequence of both a specific topographical shape and changeable meteorological conditions in this Icelandic fjord region. Despite of this, slush flows get only low interest from geomorphologists, and just a little is known on their geomorphological impact.

Topographical conditions are gathered in many places of the Westfjords, but especially in Bíldudalur surroundings: below a plateau area, two wide funnels notch the subvertical rockwall between 150 and 460 m in altitude, while large talus cone develop downslope, almost to the sea. Winter meteorological conditions are dominated by heavy perturbed weather and frequent temperature changes around frost point, which are favourable to weak cohesion of the snow cover.

The five most recent cases, which date from 1997 and 1998, get bigger interest than previous events, mostly because of its implications in natural hazards. After a 80

meteorological analysis of the triggering factors of slush flows, their geomorphic impact is studied from profile made along the main affected talus slope: while segments show the topographical characteristics of the slope, sedimentological measurements underline the talus features, and botanical considerations suggest both dynamic and relative dating of the deposits on the talus slope. Comparisons with other talus cone profiles, that are not affected by this process, attest the geomorphic impact of slush flows, carrying downslope a large amount of debris and getting both erosive and accumulative impacts, while snow avalanches get commonly a low efficiency in north-western Iceland, at present time.

Writing historical records, as Annals, reveal low slush-flow frequency, while the monthly distribution highlight the unsteady wintry snow cover stability: slush flows occur in north-western Iceland from November to May, with an activity peak in January, what is clearly different that in other arctic and mountainous countries.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Permafrost and Periglacial Dynamics Poster Session

SEDIMENT BUDGET ASSESSMENTS AS A PREREQUISITE FOR LANDSLIDE HAZARD ANALYSIS - EXAMPLES FROM ARCTIC ENVIRONMENTS IN ICELAND Thomas Glade, Rainer Bell

Analysis on landslide hazards differ significantly. Approaches range from expert judgement to highly sophisticated modelling techniques. The application of a particular approach is highly dependent on restrained budgets and time limitations. Therefore, investigations and analysis have to be focussed on the specific problem, often without considering the overall environmental setting appropriately. The inherent danger of the interpretation of results is to draw conclusions which are indeed appropriate to the current situation, but possibly not in conjunction with long-term trends.

Approaches of landslide hazard investigations include either statistical analysis of former events, mostly on small scales, or mathematically and physically based modelling of specific events in given locations considering detailed information on geotechnical, hydrologic and hydraulic parameters. Comprehensive investigations include herein current sediment storage and potential mobility of the sediment.

Unfortunately, often the reproduction of

sediment is not taken into account although the rate of refilling storages, removed by previous events, is most crucial in estimating future events.

Numerous communities in Iceland are heavily affected by many natural hazards, including landslides, and specifically rock falls and debris flows. As soon as either of these processes have occurred, sediment is partially or totally removed from the catchment. Therefore, comparable triggering conditions do not have similar process responses. In Iceland, sediment storage is refilled by continuous bedrock weathering. In addition it is suggested, that sediment is also delivered from high altitude plateaus to the slopes and channels by solifluction and frost creep processes. Although not quantified yet through measurements, it is concluded, that the delivering of sediment due to weathering and solifluction is most important for sediment availability for debris flows in the Westfjords in Iceland. The condition of sediment storage, removal, and deposition can be determined by a geomorphic assessment on sediment budgets 81

Shifting Lands. New insights into periglacial geomorphology

for the whole region before investigating the factors for debris flows hazard analysis in detail. Consequently it is suggested to include geomorphic assessments, and in particular sediment budget approaches, into detailed hazard analysis as a general procedure.

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Permafrost and Periglacial Dynamics Poster Session

SPATIAL MODELLING OF SOLIFLUCTION PROCESSES IN THE ABISKO AREA, NORTHERN SWEDEN Hanna Ridefelt

Movement monitoring of solifluction has been performed in the the Abisko area (especially in K채rkevagge) since the 1950s.

However there is little understanding of the regional constraints on solifluction distribution and movement rates and how they respond to climate change. Given the well documented increase in temperature in this sensitive subarctic environment, this study aims to model the spatial extent and variations of solifluction and explain how the environmental and climatic controls operate in this area.

More than ten different sites in the region have been selected, reflecting diverse environments, in terms of moisture availability, locations on summits or valleys and slope aspects.

Surface movement rates are measured with wooden dowels, placed in grids covering soliflucted areas as well as non-soliflucted areas on a range of slope angles. Movement profiles are obtained by vertical lines and data on frost heave rates are also obtained using CALM protocols.

Soil moisture contents at different depths and ground temperatures down to 60 cm are monitored on a year round basis. Detailed instant soil moisture values are also taken at each wooden dowel.

Preliminary ground temperature data illustrate thermal constraints between valleys (K채rkevagge) and summit environments (L책ktatj책kka), based on the extensive snow cover in the valley as opposed to the snow free summit sites. Following this the preliminary conclusions are that solifluction in valleys are mainly caused by snow melt, while solifluction in the snow free summit environments is related to ice lense formation causing frost heave, including sorting.

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Permafrost and Periglacial Dynamics Poster Session

SORTED PATTERNED GROUNDS IN MARGINAL ZONES OF FLÁAJÖKULL (SE ICELAND) AND ELISBREEN (NW SPITSBERGEN).

Maciej Dabski Laboratory of Sedimentology, Faculty of Geography and Regional Studies University of Warsaw, Krakowskie Przedmiescie 3000-927 Warsaw, Poland mfdbski@uw.edu.pl

Research on sorted patterned grounds developed within glaciers’ marginal zones created during LIA deglaciation are not reported frequently. Among few works one should mention Ballantyne and Matthews (1982, 1983), Harris and Matthews (1984), Matthews et al. (1998) who conducted research in Jotunheimen, Norway. Dabski and Gryglewicz (1998) described forms of frost sorting in marginal zone of Fláajökull in SE Iceland.

Following research aims to compare two markedly different climatic regions: SE Iceland (cool maritime temperate zone) and NW Spitsbergen (maritime high-arctic zone).

Both zones lie on similar altitude of about 30 to 80 m a.s.l. Since values and annual variations of temperature, precipitation, snow cover strongly influence development of patterned grounds, it can be expected that sorted patterns within the two marginal zones are much different.

In general forms of superficial sorting within the two moraine zones are not well developed are not easily found. The most distinguished forms are presented in the following figure.

Presented Icelandic forms can be classified as 84

small-scale nets and stripes (Washburn, 1956) and are developed on lee side of recession moraine ridge deposited about 85 year ago (Dabski, 2002). Analogue Spitsbergen forms, nets and stripes of slightly larger scale, are developed within upper parts of terminal moraine ridge about 100 years old (Lankauf, 1999).

In both places vertical sorting is limited to very shallow ground layers (10 – 20 cm). Clasts in the coarse borders of nets display rather chaotic orientation except for places where lateral pressure due to solifluction imposes orientation parallel to the boarder’s direction.

Granulometrical analysis of Fláajökull till display less silt content comparing with Elisbreen till, however both sediments are frost-susceptible according to Beskow (1935).

Structure of the forms suggests differential frost-heaving mechanism. In Icelandic conditions the smaller forms where initiated probably due to needle-ice action. Presence of permafrost in Elisbreen marginal zone does not seem to play the prime role in development of the forms since there are no signs or cracking not circulation of active layer. Thus the forms are probably initiated

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

by differental built-up of segregated ice.

Much smaller and poorly developed frostsorted surfaces, sometimes only individual nets, boulder-cored frost boils (Harris, Matthews, 1984), are also encountered within younger moraines in both marginal zones. Larger forms of superficial sorting such as stonefilled furrows (Dabski, Gryglewicz, 1998) which sometimes merge to form encircling patterns are found mainly within older, terminal moraines of both marginal zones.

They are probably developed by gravitation movements of larger clasts due to differential melt-out of dead ice (Corte, 1966).

It is concluded that despite major regional climatic differences between SE Iceland and NW Spistbergen, the periglacial modification of glaciers’ marginal zones is similar. Young age of sediments and local paraglacial factors exert very important role in development of superficial sorting.

References Ballantyne, C.K., Matthews, J.A. (1983). Dessication Cracking and Sorted Polygon Development, Jotunheimen, Norway. Arctic and Alpine Research, Vol. 15, No. 3, 339-349.

Ballantyne, C.K., Matthews, J.A. (1982). The Development of Sorted Circles on Recently Deglaciated Terrain, Jotunheimen, Norway. Arctic and Alpine Research, Vol. 14, No. 4, 341-354.

Beskow, G. (1935). Tjälbildningen och tjällyftningen með särskild hänsyn till vägar och järnvägar. S. Geol. U., ser.

C, pp. 375.

Corte, A.E. (1960). Experimental formation of sorted patterns in gravel overlying a melting ice surface.

Biuletyn Peryglacjalny, 8, 65-72.

Dabski, M. (2002). Dating of the Fláajökull moraine ridges, SE – Iceland; comparison of the glaciological, cartographic and lichenometrical data. Jökull, 51, 1724.

Dabski, M., Gryglewicz, E., (1998) Selected forms of frost sorting in the marginal zone of Fláajökull (Iceland). Biuletyn Peryglacjalny, 37, 19-34.

Harris, C., Matthews, J.A. (1984). Some Observations on Boulder-cored Frost Boils. The Geographical Journal, Vol. 150, No. 1, 63-73.

Lankauf, K.R. (1999). Recesja Lodowców rejonu Kaffiöyry (Ziemia Oskara II – Spitsbergen) w XX wieku. Rozprawa doktorska.

Matthews, J.A., Shakesby, R.A., Berrisford, M.S., McEwen, L.J. (1998). Periglacial Patterned Ground on the Styggedalsbreen Glacier Foreland, Jotunheimen, South Norway: Micro-Topographic, Paraglacial and Geoecological Controls. Permafrost and Periglacial Processes, 9, 147-166.

Washburn A.L. (1956) Classification of patterned ground and review of suggested origins. Bulletin, Geological Society of America, 67, 823-865.

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Permafrost and Periglacial Dynamics Poster Session

SHALL WE RECONSIDER THE PROCESSES CONTROLLING THE SPATIAL DISTRIBUTION AND THE EVOLUTION OF PERMAFROST IN AN ALPINE ENVIRONMENT ?

Reynald Delaloye Department of Geosciences, Geography, University of Fribourg, Switzerland Reynald.Delaloye@unifr.ch

What are the key mechanisms controlling the occurrence and the evolution of mountain permafrost in peripheral aeras, i.e. where the presence of permafrost is strongly discontinuous, isolated, or even uncertain ?

The question is the focus a recent PhD project achieved in the Swiss mountains.

Four types of permafrost terrain are analysed, namely : (a) scree slopes at low elevation (6501700 m a.s.l.); (b) talus slopes at high elevation (2200-3000 m a.s.l.); (c) inactive/relict rock glaciers; (d) historical (Little Ice Age) forefield of small glaciers. About twenty sites are investigated by means of electrical resistivity and ground temperature (instantaneous or continuous) measurements. Weather and snow data have been also permanently recorded on several sites between 1997 and 2004.

The results show that it is necessary to consider the spatial distribution of permafrost in an alpine environment as being the superposition of two modes in which the thermal mechanisms differ : a typical mode mainly resulting from a 1-dimension energy balance whose components are primarily 86

conductive and convective heat fluxes, and an atypical mode strongly influenced by an advective component of the energy balance.

At least two processes generating, or having generated, an atypical distribution of permafrost in non-consolidated sedimentary deposits are highlighted : the effects of the Little Ice Age glacier advance and an internal circulation of air (“chimney effect” or “wind tube”).

In the historical glacier forefields, the occurrence of permafrost is often limited to the margins of the former proglacial field; moreover, frozen materials can have been moved and significant imbalances, as much thermal as geometrical, can have been caused by the glacier advance.

In open-voids blocky accumulations (talus slopes, inactive and relict rock glaciers), an internal ventilation mechanism, which reverses and intensifies according to the contrast in temperature with the surrounding air, is crucial to allow the occurrence of permafrost in low elevation talus slopes where it can lead to a negative thermal

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

annual anomaly of the ground up to 3 to 7°C. Ground temperature measurements show in any case the existence, certainly attenuated, of the ascending winter phase of the ventilation system in talus slope at high elevation and in inactive/relict rock glaciers.

It is indeed possible that such a circulation of air also contributes to determine the spatial distribution of permafrost in the talus slopes and to preserve materials in a permanent frozen state for thousands of years in inactive or apparently relict rock glaciers.

In conclusion, we have to keep in mind that one or the other of these â&#x20AC;&#x153;advectiveâ&#x20AC;? processes may affect or have affected the permafrost conditions in any accumulation of materials and that it is necessary to take this into account for a reliable estimate of the effects of the climate warming on the evolution of mountain permafrost and its spatial distribution.

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Shifting Lands. New insights into periglacial geomorphology

Permafrost and Periglacial Dynamics Poster Session

THE STUDY OF RELICT FORMS FOR THE RECONSTRUCTION OF PAST PERIGLACIAL ENVIRONMENTS IN THE ITALIAN MOUNTAIN CHAINS AIGeo Working Group (Italy) “Past distribution of the periglacial environment in the Italian mountain chains: reconstructions based on the study of relict forms”: 2 3 4 5 1 Casarosa N. 1, Chelli A. , Firpo M. , Ginesu S. , Guglielmin M. , Pappalardo M. , Pecci M. 6 3 1 7 7 4 , Queirolo C. , Ribolini A. , Robustelli G. , Scarciglia F. , Sias S. , Tellini C. 2 Dipartimento di Scienze della Terra, Università di Pisa; Dipartimento di Scienze della Terra, Università di Parma; 3 Dipartimento per lo Studio del Territorio, Università di Genova; 4 Istituto Scienze Geologico-Mineralogiche, Università di Sassari; 5 ARPAL, Lombardia; 6 ISPESL-Dipartimento Insediamenti Produttivi e Interazione con l’Ambiente, Roma; 7 Dipartimento di Scienze della Terra, Università della Calabria.

1 2

At the end of 2002 a Working Group within the Italian Association of Physical Geography and Geomorphology (AIGeo) started its three-year activity, with the main aim to assess possible periglacial conditions occurred during past glacial stages. The research team focuses on the analysis of relict features (landforms and associated deposits), by comparing materials, methodologies and results of one’s own research on the periglacial environment, and the attempt to fix their chronology. Although present-day and Quaternary distribution of permafrost in Italy has been recently reconstructed by means of typical landforms, such as rock glaciers (Dramis and Guglielmin, 1999), the genesis of many other landforms, usually interpreted as related to periglacial processes, is not yet clear.

Scree taluses and block streams/fields, very recurrent on moderately steep slopes in the 88

Apennines and in Sardinia, and not related to any present-day morphoclimatic environment, are being investigated. Since sedimentary facies cannot be always univocally interpreted because possibly produced by different processes and often involved by significant post-depositional changes, the WG is trying to collect evidence about their genesis, whether really periglacial or not, investigating the role of frost weathering in sediment supply and maybe seasonal freezing and cryonival phenomena rather than permafrost in sedimentary processes, and consequently to use typical periglacial (relict) landforms for Quaternary paleoclimatic reconstructions in Italy.

After comparing the different types of landforms/deposits outcropping in the study areas (Fig. 1), separately investigated by the WG members, a work sheet for a standard

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description of their main characters and for possible data base implementation was prepared, and is being tested and applied at the various study sites.

A statistical approach (eigenvalue and spherical variance methods, recently applied

by Bertran et al., 1997) to support and compare the classical geomorphological and sedimentological description of scree deposits has been successfully performed on éboulis ordonné-types. It is based on the evaluation of the fabric strength/randomness of clasts by measuring a-axis orientation and dip, and revealed to be a good discriminator of sedimentary processes.

Fig.1 - Location map of the study sites

References Bertran P., Hétu B., Texier J.P., van Steijn H. 1997. Fabric characteristics of subaerial slope deposits. Sedimentology, 44, 1-16.

Dramis F, Guglielmin M. 1999. Permafrost investigations on the Italian mountains: the state of the art. In: Paepe R., Melnikov V. (Eds.) Permafrost response on economic development, environmental security and natural resources. Kluver Academic Publishers, 259-273.

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Shifting Lands. New insights into periglacial geomorphology

Permafrost and Periglacial Dynamics Poster Session

LATE QUATERNARY TERRESTRIAL RECORDS FOR A PERMAFROST SITE NEAR THE IMPACT CRATER LAKE ELâ&#x20AC;&#x2122;GYGYTGYN, CHUKOTKA, NE SIBERIA Georg Schwamborn, Lutz Schirrmeister, Christine Siegert, Hanno Meyer, Hans.-W. Hubberten, Grigory Fedorov*.

Alfred-Wegener-Institute for Polar and Marine Science, Telegrafenberg A43, Potsdam, Germany * Arctic and Antarctic Research Institute, Bering Street, St. Petersburg, Russia

Various types of patterned ground indicate that permafrost builds up the bottom of the impact crater holding Lake Elâ&#x20AC;&#x2122;gygytgyn, NESiberia, and periglacial conditions influence the properties of sediments being washed into the lake basin. For its impact crater age of ~3.5 Ma future deep drilling of lake sediments is planned to reach in time beyond the northern glaciation cycles during the Pliocene.

The presented permafrost studies focus on properties of terrestrial deposits in the catchment area of Lake Elgygytgyn in order to use their potential as Late Quaternary paleo-environmental archives for climatic reconstruction of the region.

Firstly, paleoclimate archive analysis is applied to an ice wedge formation, which is ca. 100 cm in greatest width and 500 cm in total height.

It uses oxygen isotope methods similar to those in glacial studies and are supported by hydrochemical measurements (i.e. major anions and cations). The oxygen isotope 90

signal is related to winter precipitation and first snowmelt occurring during early spring filling ice cracks. This discrete ground ice formation is expected to cover Holocene to late Pleistocene time. The ice wedge network began presumably to grow starting from frost fissures on an emergent ice-rich slope sediment surface as can be seen at the bottom of the formation. The current cold climatic phase is evident by the formation of close meshed ice wedge polygons (10-15 m in diameter) above a wide meshed polygon system (about 50 m in diameter) at the bottom.

Secondly, after a GPR pre-survey, sediment samples of an undisturbed, five meter deep frozen core sequence were taken in close vicinity to the ice wedge. The cryostructure and ice content here result from repeated thawing-freezing-cycles of the soil water within the paleo active layer. Environmental changes are deduced from the oxygen isotope signal discontinuities, from changes of the heavy mineral composition within the sediments as well as for grain size morphology,

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

which is related to transport mechanisms (such as eolian, fluvial or gravitational, sloperelated movement). Plant remains in the sediments will be used for radiocarbon age determination. Pollen stratigraphy allows the vegetation reconstruction.

Periglacial environmental changes are thought to trigger sediment export into the lake and we study periglacial (ground ice, sedimentary and cryosedimentary) properties to amend paleoclimate reconstructions using lake sediment records.

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Nival and Snow-Related Processes Session Oral Paper

THE ROLE OF NIVAL PROCESSES FOR MODERN AND PLEISTOCENE LANDSCAPE GENESIS IN NORTHEAST SIBERIA L. Schirrmeister*, G. Grosse*, V.V. Kunitsky**, A.J. Dereviagin*** *Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, Germany ** Permafrost Institute Yakutsk, Russian Academy of Science, Yakutia *** Moscow State University, Faculty of Geology, Russia

Various morphological forms connected with snow accumulations in snow patches shape the modern periglacial surface of Arctic Siberia.

Nival niches, i.e. the sites of snow patches, are important places for modern erosion processes in the coastal plains as well as Arctic seacoasts. This means modern thermoerosion and thermoabrasion are strongly connected with nival processes. Due to the treeless tundra the low winter precipitations are often blown together into depressions or in front of terrace edges. Many snow patches occur at the slopes of coastal mountain ranges around the Laptev Sea, some of which are perennial.

Rock weathering in Arctic regions is very active around snow patches. In addition, snow accumulation along coastal ranges feeds numerous small rivers and brooks. They are the most important transporters of clastic matter from the mountains to the coastal plains.

Late Pleistocene ice-rich deposits of the socalled Ice Complex, the widest distributed permafrost formation in the Arctic Siberian lowlands, were probably accumulated as a result of the increased occurrence of snow patches during this period. A 20 to 50 m thick 92

layer of Ice Complex deposits covers the coastal lowlands in front of the coastal ranges around the Laptev Sea. The coastal plain surface, which is dominated by thermokarst depressions and thermoerosional valleys, provides a large number of sites for snow accumulation.

Elevated tundra areas are more or less free of snow during winter, but valleys and basins are filled with snow. In the same way, snow blown from the sea ice that has accumulated along coastal cliffs form large snowdrifts. Snow accumulations are often protected against the sun in deeper valleys, slopes and cliffs with a northern orientation. Therefore, they can partially survive up to the Arctic summer or longer, which is recognizable in satellite pictures.

This talk will present field observations data from the Laptev Sea area gathered over the last five years. Various types of nival relief types are shown as well as satellite pictures and snow and sediment characteristics.

In addition, the idea of Late Pleistocene landscape genesis controlled by nival processes will be explained.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Nival and Snow-Related Processes Session Oral Paper

NIVAL BEDROCK EROSION AT A SEASONAL SNOW PATCH SITE FROM THE CUIÑA CIRQUE, ANCARES SIERRA, NORTHWESTERN SPAIN M. Valcárcel-Díaz, P. Carrera-Gómez, A. Pérez-Alberti Department of Geography, University of Santiago de Compostela, Santiago de Compostela, Spain Correspondence to: Dr. M. Valcárcel-Díaz, Departamento de Xeografía, Facultade de Xeografía e Historia, University of Santiago de Compostela, Praza da Universidade 1, 15.782-Santiago de Compostela (A Coruña), Spain.

E-mail: marcosvd@usc.es

Seasonal, late-lying snow cover plays a main role in present-day rock weathering on the highest portions of the northwestern Spanish mountains. In this communication we focus on the mechanical erosion exerted over the bedrock by a snow patch located in the Cuiña Cirque, Ancares Sierra. The snow patch extends over the northeast-facing sector of the cirque backwall, between 1,820 and 1,930 m.a.s.l. It overlies a substrate composed of densely jointed, near horizontal beds of Ordovician shales and quartzites. Bedrock shows a stepped topography formed by a series of superimposed narrow, nearly flat benches overhung by small steep walls, that facilitates snow accumulation. The snow patch usually begins to form by midNovember and completely disappears by late July. It thickness is very uneven, reflecting substrate irregularities. Maximum depths slightly exceeding 6 m. have been measured at the cirque edge, where most of the snow blown from the surrounding windward slopes is redeposited. A hard and continuous basal ice layer up to 30 cm. thick have been identified during one ablation season. The movement of the snow patch over the bedrock

produces detachment and transport of rock fragments of very different size, from small chips to metric blocks. Bedding and jointing planes pattern facilitates plucking. Annual displacements of up to 11 m. have been measured for loose clasts. Removed debris are deposited at the downslope margin of the snow pacht, forming an arcuate protalus rampart. Displaced, subnivally dragged rock fragments usually show worn edges, scratches and striae. Crushed clasts are very common and rock flour has been observed below some abraded rock slabs. Bedrock also shows a variety of nival erosional features.

Lichen-free, abraded and polished surfaces are ubiquitous. Smoothed surfaces show plenty of scratches, striae, abrasion tracks and small grooves. Striae are best defined on finegrained shale. Large abrasion tracks up to 70 cm. long and 1.5 cm. wide have been found on quartzite outcrops. Both striae and abrasion tracks are broadly aligned with snow patch displacement direction. The geomorphic activity of the snow pacht is mainly attributed to snowcreep and snowslide, although slab ground avalanches exceptionally can occur.

The erosional behaviour of the snow patch 93

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is currently irregular on a year-on-year basis. It is strongly dependent on the total amount of snow precipitation and, therefore, on snow patch size. Evidence from Cui単a Cirque suggests that seasonal, late-lying snow patches can carry out a significant geomorphic work.

Key words: seasonal snow patches, snowcreep, snowslide, subnival erosion, Ancares Sierra, NW Spain

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Nival and Snow-Related Processes Session Oral Paper

MultiRISK - MODELLING NATURAL RISKS AND ITS APPLICATION UNDER ASPECTS OF GLOBAL WARMING AND LAND-USE CHANGES IN NORTHWEST ICELAND Thomas Glade, Kirsten von Elverfeldt

Snow avalanches, slush flows, rock falls, and debris flows are an enormous thread to population and infrastructure in mountainous areas, posing different risks within the same region and locality. To obtain a comprehensive natural risk assessment a multi-processual approach is therefore essential. Currently, the respective processes are modelled in different software programmes with separate data management, whereas only the results of the single processes are finally summarized and displayed in a GIS. Therefore, fundamental research is needed regarding integrative and multi-processual modelling of natural risks, in order to develop a comprehensive, modular risk analysis tool with a high temporal and spatial resolution. Such a model has the potential to calculate different natural risks for one area, e.g. with seasonal differentiation.

The aim of this project is to attain a computer-based natural risk model for different processes (rock fall, snow avalanches, debris flows and slush flows) which will be developed in Northwest Iceland and applied to calculate scenarios of global warming and land-use change. The respective process models will be integrated as modules in an open GIS-platform. Using DEMs and

process parameters, hazard run-outs will be calculated and hazard zones derived. Zonation depends on the magnitude and frequency of the respective process, so that different scenarios are possible. Combining hazard zones with risk elements (e.g. people, houses, infrastructure), their damage potential, and their vulnerabilities to the respective process, natural risk zones will be deliniated. These can be displayed either for a single process or a process group or for a single object at risk or a large region.

The project is associated to the scientific natural risk analysis which includes studying the geosystem as well as the vulnerability of humans and their surroundings. Natural risk analysis has a strong application potential: In terms of protecting human beings and assets, it helps to detect and therefore reduce possible damages, maybe even prevent damage.

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Nival and Snow-Related Processes Session Oral Paper

QUANTIFYING AND MODELLING THE CONTRIBUTION OF FULL-DEPTH SNOW AVALANCHES TO THE SEDIMENT BUDGET OF HIGH-MOUNTAIN AREAS BASED ON FIELD MEASUREMENTS AND SPATIAL MODELLING Tobias Heckmann, Michael Becht Dept. of Physical Geography Catholic University of Eichstaett/Ingolstadt, Germany

Full-depth snow avalanches can contribute significantly to the sediment budget of highmountain geosystems, as it has been shown by several studies of different extent, mostly with considerably small sample sizes. This study presents an extensive dataset on the sediment yield of 115 avalanches measured in the years 2000-2003 in two study areas of the Bavarian Alps / S Germany.

Our results show that a correlation of sediment yield and geofactors of the avalanche tracks is very difficult. The combination of several modelling approaches, however, makes it possible to delineate the potential process area and zones of erosion, transport and deposition. First, a statistical disposition model established on the basis of mapped avalanche starting zones is used to define potential starting zones. Second, a 2-parameter friction model (Perla et al. 1980) is combined with a grid based random walk model (Gamma 2000) to delineate pathway and reach of the modelled avalanches along with a calculation of flow parameters such as flow velocity. Third, these model results showed a good correlation with mapped zones of erosion, transport and deposition of a well-documented avalanche event.

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Based on these results, spatial modelling of the geomorphic activity of full-depth snow avalanches is possible.

This study is part of the SEDAG research project (SEDiment cascades in Alpine Geosystems) conducted by 5 working groups aiming at the quantification and modelling of geomorphic processes associated with the sediment budget. As spatial models of the geomorphic activiy exist for several processes, an overlay of their results can show zones of predominant erosion or deposition as well as areas where two or more processes interact, i.e. where sediment is delivered from one process to another. The interaction of full-depth snow avalanches with hillslope and channel fluvial processes exemplifies, on the basis of field data, the potential of our approach.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Nival and Snow-Related Processes Session Oral Paper

MORPHOLOGICAL IMPACT OF GROUND SNOW AVALANCHES IN ICELAND Þorsteinn Sæmundsson1, Armelle Decaulne2 Natural Research Centre, of North-western Iceland, Adalgata 2, 550 Saudarkrokur, Iceland Physical Geography Laboratory UMR 6042 CNRS, GEOLAB, Maison de la Recherche , 4 rue Ledru, F-63057 Clermont-Ferrand, France 1 2

Snow avalanches can and do under certain weather condition transport considerable amounts of debris down into the lowlands, and are in that sense significant sedimentary transport process. This process has until recently not been regarded as an important sedimentary process in Iceland and not recognized as such.

By the use of sedimentological and stratigraphical methods, debris transported with snow avalanches can be recognized in the field and distinguished from other types of sediments (Blikra 1994, Blikra & Nemec 1998, Blikra & Sæmundsson 1998, Sæmundsson, Petursson & Decaulne 2003). The geological data can thus be used in combination with other methods to evaluate potential impact of snow avalanches in the run-out zones. Studies of this kind have only recently attached attention in avalanche-hazard evaluations.

From 1995 extensive studies of morphological impact of ground snow avalanches have been carried out in NW-, N- and E-Iceland.

The main studies have been focused on the morphological impact of snow avalanches that occurred during a heavy snowstorm in October 1995. Then a series of snow avalanches carrying large quantities of debris

occurred in the northern and north-western parts of Iceland, clearly demonstrating the significance of this type of sedimentary transport. These snow avalanches were caused by somewhat unusual weather condition. Prior to the storm the weather had been mild and the ground was unfrozen and snow free, also upon mountain slopes. Due to these conditions the snow avalanches were able to erode their pathways, and transport large quantities of sediments, a mixture of grain sizes between silt and boulders, down into their run-out zones.

References Blikra, L.H. 1994: Postglacial colluvium in Western Norway: Sedimentology, Geomorphology and paleoclimatic record.

Unpubl. Dr.Scient. thesies, University of Bergen, 261 pp.

Blikra, L.H. & Nemec, W. 1998: Postglacial colluvium in western Norway: depositional processes, facies and palaeoclimatic record.

Sedimentology, 45. 909-959.

Blikra, L.H. & Sæmundsson, Th. 1998: The potential of sedimentology and stratigraphy in avalanche-hazard research. 25 Years of Snow Avalanche 97

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Research, Voss 12-16 May 1998.

Norwegian Geotechnical Institute.

Publication Nr.203. 60-64.

SĂŚmundsson, T, Petursson, H.G. & Decaulne, A. 2003: Triggering factors for rapid mass movements in Iceland. In: DebrisFlow Hazards Mitigation, Prediction and Assessment. Rickenmann & Chen (eds).

Millpress, Rotterdam, pp. 167-178.

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Nival and Snow-Related Processes Session Oral Paper

SNOW DISTRIBUTION AND BIOCOMPLEXITY IN ALPINE LANDSCAPES: A PROGRESS REPORT Robert G. Björk, Ulf Molau Botanical Institute, Göteborg University, Box 461, SE-405 30 Göteborg, Sweden robert.bjork@botany.gu.se, www2.botany.gu.se/research/Latnja/latnja.html

Snowbed ecosystems make up a pronounced component throughout the tundra biome, particularly in alpine areas due to the ragged topography and wind re-distribution of snow. As there are species and communities restricted to the snowbed habitat, they make a unique component in the alpine biodiversity at scales from species to landscapes. In connection with the Global Warming forecast, snowbed ecosystems of alpine Europe are regarded as particularly vulnerable in IPCC’s 2001 assessment report.

when the food supply have started to run short.

Snowbeds also provide important ecosystem services to the landscape such as maintaining the adjacent earlier-thawing ecosystems by steady water and nutrient supply, and by ensuring good winter conditions for lemmings. During years of low density the lemming preferentially grazes in snowbeds. Furthermore, snowbeds is the plant community of utmost importance for reindeers, and the availability of snowbeds in the landscape can influence the well-being of reindeers by having the possibility to offer nutrient rich food late in the growing season

As tundra ecosystems are typically limited by nitrogen availability as well as temperature, Climate Change and a likely exponentially increasing deposition of plant-available nitrogen with the precipitation are inevitably accelerating processes that will alter the structure and extent of this key ecosystem.

The winter weather conditions are those that are primarily responsible for the variability in the snowbed morphology, while the local topography sets the general snowbed pattern.

However, the summer weather conditions are also implicated in the variation of rate and pattern of snowmelt between years, though the general snowbed outline remains consistent among years.

The project “Snow Distribution and Biocomplexity in Alpine Landscapes” is running at Latnjajaure Field Station, in northern Swedish Lapland, where four snowbed plant communities are studied. The 99

Shifting Lands. New insights into periglacial geomorphology

snowbeds are of the â&#x20AC;&#x153;moderate typeâ&#x20AC;?, which means that they are melting out before the end of July, and they are situated in both heath and meadow sites. Our current studies include, e.g., monitoring of snow dynamics, plant community structure in fertilized and control plots, lemming population dynamics, nitrogen and debris deposition, and soil processes. We will report on the progress of this ongoing project.

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Groupe Français de Géomorphologie (GFG)

Sixième Journée des Jeunes Géomorphologues

Clermont-Ferrand 22 janvier 2005

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6e Journée des Jeunes Géomorphologues ESTIMATION DES BILANS DE MASSE GLACIAIRE PAR INTÉGRATION D’HÉRITAGES GÉOMORPHOLOGIQUES DANS DES MODÈLES NUMÉRIQUES DE TERRAIN : APPLICATION À TROIS GLACIERS DU MASSIF DES ECRINS. Etienne COSSART Equipe DYNMIRIS, Université Denis Diderot – Paris 7 UMR 8586 – CNRS 75251 Paris Cedex 05 ecossart@yahoo.com

Le bilan de masse est la différence de volume d’un glacier entre deux dates données, elle est souvent rapportée à la superficie du glacier et s’exprime donc comme une variation d’épaisseur en mètres équivalent eau. Ce paramètre constitue une variable indispensable à toute étude géomorphologique des marges glaciaires car elle détermine (1) le volume d’eau stocké ou déstocké par le glacier et (2) des variations du niveau de base local, constitué par la surface du glacier.

Deux méthodes sont envisageables pour calculer ce bilan de masse : l’une, directe, consiste à mesurer les variations d’épaisseur du glacier (triangulation, GPS…) tandis que l’autre, indirecte, vise à reconstituer les variations d’épaisseur à partir des héritages glaciaires. Cette seconde méthode présente le double avantage de pouvoir inférer le bilan de masse sur des périodes passées et d’être applicable sur des glaciers qui n’ont actuellement fait l’objet d’aucune mesure stationnelle.

Nous cherchons ici à préciser cette méthode et à l’appliquer sur trois glaciers du Massif des Ecrins depuis la fin du XIXe siècle. La première 102

étape est de cartographier l’ensemble des héritages glaciaires et de les insérer dans une succession chronologique : nous en déduisons l’altitude atteinte par les glaces. En intégrant ces données dans un SIG raster et en les combinant avec des Modèles Numériques de Terrain nous pouvons simuler la géométrie du glacier en trois dimensions pour des périodes passées (fig. 1). La limite de cette méthode est que les héritages glaciaires ne permettent une simulation précise que dans la partie aval des glaciers, nous avons donc cherché à développer un algorithme permettant d’estimer le bilan de masse sur l’ensemble d’un glacier à partir des résultats acquis dans sa partie aval.

Un exemple de résultat est ici donné pour le glacier du Casset, entre 1928 et 1975 (fig. 2).

Les résultats obtenus permettent d’estimer les pertes de volume à 22 et 24 millions de mètres cubes entre 1880 et 1975 pour les glaciers de Séguret-Forant (bassin-versant du Gyr) et du Casset (bassin-versant de la Guisane), respectivement. La perte s’élève même à 94 millions de mètres cubes dans le cas du glacier Sélé (bassin-versant de la Gyronde).

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

Figure 1

Figure 2 103

Shifting Lands. New insights into periglacial geomorphology

6e Journée des Jeunes Géomorphologues ETUDE PALÉOGÉOGRAPHIQUE DU MASSIF DE LA CHARTREUSE Morgane LE DARZ Doctorante en Géographie au laboratoire EDYTEM CNRS UMR 5204 Centre Interdisciplinaire Scientifique de la Montagne Campus Scientifique F 73376 – Le Bourget du Lac cedex Tél. 04 79 75 88 77 Mèl : morgane.le-darz@univ-savoie.fr

Jusqu’alors, le massif de la Chartreuse n’a jamais fait l’objet d’une étude géomorphologique approfondie en relation avec les glaciations quaternaires. Pourtant, l’analyse des héritages glaciaires (s.l.) pléistocènes qui y ont été conservés permet d’apporter des connaissances nouvelles tant sur la dynamique des grands courants glaciaires quaternaires que sur les paléogéographies du massif lui-même.

A l’échelle des Alpes françaises nordoccidentales, le massif de la Chartreuse se situe sur le front de la chaîne alpine. Par sa situation d’interface entre la haute montagne alpine et le piémont, sa situation géographique présente plusieurs intérêts paléogéographiques. Le massif a connu précocement les prémices de la déglaciation, ce qui permet de retrouver l’enregistrement de l’évolution climatique et environnementale à des altitudes variées dès la fin du Pléniglaciaire à une période où les sites intra-alpins étaient encore englacés. En outre, ce massif est situé au carrefour de deux glaciers majeurs (Rhône, Isère) ce qui permet de mieux comprendre la dynamique de ces 104

appareils glaciaires lorsqu’ils se trouvent à l’aval des grands bassins d’accumulation (Valais, Mont-Blanc, Beaufortain, Vanoise…).

En effet dans le haut piémont, l’organisation spatiale des flux glaciaires est encore mal connue.

A l’échelle du massif lui-même, les données à la fois géographiques et géologiques permettent la reconstitution des paléogéographies pléistocènes. Les grandes surfaces d’altitude formées par les hauts plateaux calcaires ainsi que les dépressions topographiques ont favorisé l’action conjointe de deux dynamiques glaciaires. L’une active, par la formation d’appareils glaciaires locaux sur les sommets et l’autre passive, par le biais des pénétrations de glaces alpines dans la Chartreuse. Enfin, la Chartreuse est un massif karstique qui fonctionne comme un véritable piège à sédiments (glaciaires, lacustres) qui contribue à un enregistrement continu de son histoire glaciaire.

Ce travail de levé systématique des héritages glaciaires quaternaires du massif de la Chartreuse a été réalisé en faisant appel aux

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

méthodes de la géomorphologie classique : travail de terrain, reconnaissances et caractérisation des formes et des formations glaciaires, étude de leurs organisation stratigraphique (géométrie, agencement…).

Par le biais de cette approche, nous avons pu mettre en évidence des modèles de fonctionnement glaciaires similaires entre les bassins nord et sud du massif avec une forte interaction entre les apports de glaces extérieures (diffluences alpines) et les glaces locales (glaciers autochtones). Ce système de dynamique glaciaire s’explique en partie par les caractéristiques topographiques et climatiques de la Chartreuse : la présence de nombreuses zones d’altitude et l’exposition au flux d’ouest sont autant de paramètres qui favorisent des accumulations glaciaires potentielles et le développement de nombreux glaciers locaux. Enfin, ce travail de recherche a permis de revoir totalement l’extension des paléo-lacs quaternaires de ce massif qui n’ont jamais été mis en évidence jusque là.

Mots-clés. Chartreuse, Préalpes, Quaternaire, héritages glaciaires, paléogéographie, géomorphologie.

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6e Journée des Jeunes Géomorphologues MISE EN ÉVIDENCE GÉOMORPHOLOGIQUE DES MODALITÉS DE L’INSTABILITÉ CHRONIQUE DU VERSANT OCCIDENTAL DU MONT MARGÉRIAZ (SAVOIE, FRANCE).

François AMELOT Laboratoire EDYTEM – CNRS UMR 5204 – CISM – Campus Scientifique F 73376 – Le Bourget du Lac Cedex Méls : francois.amelot@univ-savoie.fr, jdela@univ-savoie.fr

1. Contexte et problématique Ce travail de thèse (Laboratoire EDYTEM) entre dans le cadre du programme INTERREG III A - Alcotra “Rockslidetec”, qui a pour objet à terme, le transfert auprès des décideurs d’outils méthodologiques pour la détection et la propagation des éboulements en masse. Notre recherche porte sur le thème des approches géomorphologique et hydrogéologique des grands écroulements rocheux des préalpes de Savoie, afin d’alimenter une base de données des avalanches rocheuses qui est en cours d’élaboration avec nos partenaires.

Nous présentons ici l’écroulement de Plaimpalais, typique des avalanches rocheuses complexes du domaine subalpin. Il a été intégré dans une étude complète du versant occidental très instable du Mont Margériaz (1845 m), dans la vallée du Noyer (Savoie).

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2. Approche géomorphologique versant instable

d’un

L’étude de ce versant s’appuie essentiellement sur des relevés de terrain. Les méthodes d’investigation utilisées sont celles, complémentaires, de la géomorphologie et de la géologie : cartographie géomorphologique précise au 1/10 000, relevés GPS (situation des blocs rocheux), analyse de photographies aériennes, sondages mécaniques dans les dépôts (tarière), tomographies électriques, relevés structuraux des niches d’arrachement...

Nous avons pu ainsi mettre en évidence plusieurs grands glissements dans des marnes et marno-calcaires, de fréquents tassements de versant et mesurer l’emprise spatiale de l’écroulement de Plaimpalais (34 .106 m3), phénomène catastrophique majeur.

Ces phénomènes morphogéniques ont pu être hiérarchisés dans le temps, et une étude poussée de l’écroulement de Plaimpalais a été

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

menée, révélant outre l’effondrement du crêt calcaire sommital une forte implication des terrains marneux dans le volume mobilisé et la dynamique de propagation de l’avalanche rocheuse.

Mots-clefs : Dynamiques de versant, avalanches rocheuses, géomorphologie, Préalpes calcaires, Savoie.

3.

Croisement des analyses géomorphologique et géologique pour la compréhension de la dynamique de versant L’analyse géomorphologique du versant a mis en évidence une certaine homogénéité dans la répartition spatiale des diverses niches d’arrachement : elles sont toutes situées entre 1300 et 1400 m d’altitude (sauf pour l’écroulement de Plaimpalais : 1845 m). Cette zone critique correspond, en fait, à la fois au passage d’un chevauchement majeur et à une limite lithologique tranchée entre des marnocalcaires et des marnes gréseuses.

4. Conclusions et perspectives Ainsi, l’écroulement de Plaimpalais comme les différents glissements et tassements de versants alentours sont les symptômes révélateurs d’une structure géologique particulièrement favorable aux mouvements de versant de grande ampleur. Elle est caractérisée par la présence d’une structure chevauchante associée à un contexte lithologique marqué par l’alternance de roches dures et de roches tendres.

L’étude du site de Plaimpalais permet de faire ressortir les éléments de premier ordre dans la genèse des écroulements rocheux. A partir de ce site pilote, la recherche de contextes morpho-structuraux similaires permet de faire émerger d’autres sites d’avalanches rocheuses qui n’avaient pas été jusque là décrits.

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Shifting Lands. New insights into periglacial geomorphology

6e Journée des Jeunes Géomorphologues ORTHOPHOTOGRAPHIES ET SIG : DES OUTILS POUR LA CARTOGRAPHIE GÉOMORPHOLOGIQUE ET L’ÉTUDE DES FLUCTUATIONS GLACIAIRES RÉCENTES (1850 À 2000) Sylvain JOBARD Laboratoire EDYTEM, CNRS - UMR 5204 Université de Savoie – CISM, Bât. Belledonne 73370 LE BOURGET DU LAC Cedex Tél.: +33(0)4 79 75 81 71 – Fax : +33(0)4 79 75 87 77 e-mail : sylvain.jobard@univ-savoie.fr

Les études sur les glaciers alpins sont aujourd’hui focalisées sur les enregistrements climatiques. Les aspects morphologiques des fluctuations glaciaires restent peu utilisées car les variations de surfaces et de longueurs sont issues d’une structuration complexe des paramètres atmosphériques. Cependant, l’approche systémique du milieu glaciaire traduit parfaitement ces interactions topoclimatiques. C’est donc par cette entrée que l’étude de ces changements de forme est abordée, par le biais de reconstitutions des extensions des glaciers depuis 150 ans.

1- Le terrain d’étude.

Le site sur lequel est appliquée cette étude est le bassin versant hydrologique du Haut Arc, à la confluence du torrent du Ribon et de l’Arc, à l’aval du village de Bessans. La superficie concernée est d’environ 200 km², avec une trentaine d’appareils glaciaires de taille et d’exposition très variables.

La problématique retenue aboutit à choisir le 108

maximum de glaciers, de manière à constituer un échantillon représentatif de ce secteur des Alpes Internes.

2- La reconstitution des glaciers du Haut Arc au dernier maximum du Petit Age Glaciaire.

Les informations sont issues de l’analyse conjointe des marqueurs géomorphologiques et des documents d’archive, mais également de l’interprétation des photographies aériennes. Ces dernières sont traitées par orthorectification pour devenir parfaitement superposables à la carte topographique au 1/25 000 du secteur. Ainsi, tous les relevés de terrain et les interprétations des photos aériennes sont directement intégrés à la cartographie géomorphologique. Par cette méthode, les moraines édifiées lors du dernier stade du PAG, vers 1850-1860, sont bien identifiées et servent de base à la reconstitution de l’extension des glaciers à cette époque.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

3- Les variations de l’extension spatiale des glaciers depuis 1850 aux années 2000.

Les sources d’information principales sont les photographies aériennes de l’IGN dont les premières datent des années 1940. Ces clichés sont orthorectifiés pour être intégrés à un Système d’Information Géographique.

De même, la carte géomorphologique est géoréférencée afin d’en extraire l’extension au PAG. Enfin, les mesures des fronts des glaciers obtenues par GPS sont aussi incorporées au SIG. Toutes ces informations sont centralisées dans le but de cartographier les extensions des glaciers et de quantifier l’ampleur des fluctuations glaciaires.

L’utilisation du SIG dans la problématique de cette étude est orientée par la nécessité de centralisation des informations de nature et de source différentes. Les moteurs de ces variations ne sont pas clairement mis en évidence par cette approche et le recours à un changement d’échelle de réflexion est la perspective de recherche actuellement privilégiée.

Mots-clefs : fluctuations glaciaires, SIG, marqueurs géomorphologiques, Haut Arc (Savoie)

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Shifting Lands. New insights into periglacial geomorphology

6e Journée des Jeunes Géomorphologues ANALYSE SPATIO-TEMPORELLE DE LA DIVERSITÉ TORRENTIELLE ET ÉVALUATION DU RISQUE TORRENTIEL – EXEMPLE DE L’ARZINO (FRIULI, NORD EST DE L’ITALIE).

Florence GARLATTI Doctorante ; Université Paris VII Denis Diderot Equipe Dynamique des Milieux et des Risques (DYNMIRIS) UMR 8586 CNRS-PRODIG 2, place Jussieu, CC 7001, 75251 PARIS CEDEX 05 Tél. : 06 73 15 75 28 Mail : fgarlatti@wanadoo.fr

L’étude porte sur le Torrente Arzino, rivière préalpine et méditerranéenne inscrite dans les Préalpes Carniques orientales (Friuli, Nord-Est de l’Italie), à forte activité sismotectonique et orogénique. Affluent dextre du Tagliamento, l’Arzino est une rivière d’ordre 3 (Strahler) drainant un bassin de 119,6 km², relativement homogène à l’échelle régionale. Dans le détail, ce bassin est lithostructuralement varié où flyschs, molasses, dolomies d’une part, zones de cisaillement tectonique d’autre part, déterminent une érodibilité sélective. A ce contexte lithostructural s’ajoute une abondante pluviométrie (moyennes mensuelles variant de 117,6 mm/mois en janvier à 261,1 mm/ mois pour octobre, un maximum enregistré en septembre 1965 de 823,5 mm/mois). La combinaison de ces paramètres se traduit par des comportements (morphologiques et fonctionnels) différents des torrents élémentaires. Cette étude a pour objectif principal de qualifier et de quantifier cette 110

diversité torrentielle élémentaire afin d’en évaluer les conséquences sur le torrent collecteur, l’Arzino. Cet objectif est atteint grâce à des analyses hydromorphologiques, d’occupation des sols et des enquêtes socio-historiques, dont les résultats ont été synthétisé sous la forme d’une typologie des torrents élémentaires de l’Arzino (6 sections de vallée sélectionées). Une attention particulière a été portée aux confluences, sitestémoins de la réponse hydromorphologique du collecteur vis-à-vis de ses affluents.

L’analyse de paramètres biologiques (rapport sols nus/sols végétalisés), granulométriques et morphologiques ( hypsométrie du bassin, périmètre, aire, pente moyenne du lit, dénivelé du lit, indice de forme, densité de drainage, coefficient de drainage, relief ratio) des affluents et de leur cône (pentes du cône, dimension de l’incision, relevés de végétation, cartographie morphologique) a permis d’établir une typologie d’aléa torrentiel potentiel. Cette

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

typologie a ensuite été confrontée à une carte d’aléa torrentiel réelle établie sur la base d’une analyse hydromorphologique des confluences et des enquêtes socio-historiques.

Grâce à cette confrontation carte réelle/carte potentielle, il a été possible de hiérarchiser les divers paramètres du milieux en fonction de leur pouvoir discriminant. Mais aussi, d’analyser l’organisation spatiale de l’aléa torrentiel et enfin d’établir les bases pour obtenir une cartographie du risque torrentiel.

En conclusion, seule une approche pluri-disciplinaire permet une analyse précise de la répartition spatiale du risque torrentiel synthétisé cartographiquement. Elle fournit aussi une première évaluation de la répartition temporelle de ce risque, même si elle est limitée par la courte durée de la mémoire historique des hommes (inférieure ou égale à cent années).

Mots-clefs : aléa et risque torrentiels, hydromorphologie, enquêtes socio-historiques

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Shifting Lands. New insights into periglacial geomorphology

6e Journée des Jeunes Géomorphologues CONTRIBUTION À LA GESTION DU RISQUE TORRENTIEL EN VALLÉE DE LA CLARÉE (HAUTES-ALPES, FRANCE) Gilles GARITTE Laboratoire de Géomorphologie et Gestion des Milieux Naturels (UPRES-EA 3339) UFR de Géographie et Aménagement Université des Sciences et Technologies de Lille 59655 Villeneuve d’Ascq cedex

La vallée de la Clarée se situe dans les Hautes-Alpes à proximité de Briançon.

Contrairement aux vallées voisines occupées par de vastes stations de sports d’hiver, comme Montgenèvre et Serre-Chevalier, ouvertes au tourisme de masse à partir des années 60, la vallée de la Clarée n’a connu que récemment une reconversion vers l’économie touristique. Or, même si les institutions locales privilégient le tourisme vert et mettent en avant le patrimoine paysager de la vallée de la Clarée, de plus en plus d’aménagements dédiés à l’accueil des touristes colonisent les cônes de déjection torrentiels.

Le but de cette étude est de mieux comprendre la dynamique torrentielle des différents organismes de la vallée de la Clarée, afin de déterminer les principaux facteurs de dangerosité des torrents. Pour cela différentes méthodes d’analyse, ont été utilisées : les observations in situ complétées par des mesures topométriques au tachéomètre infrarouge, l’analyse de photographies aériennes et obliques, la recherche de données anciennes dans les archives disponibles 112

(départementales, Service de RTM, 159ème régiment de montagne…).

Les principaux résultats tendent à démontrer une nouvelle fois la complexité du phénomène torrentiel. En effet, il apparaît qu’au sein même de la vallée de la Clarée, les dissemblances en termes d’évolution, de dynamique ou de dangerosité sont très importantes d’un organisme torrentiel à l’autre. Ces différences s’expriment tout d’abord dans la dynamique récente des torrents de la Clarée. Ainsi, si tous ces torrents ont connu une réduction précoce de leur emprise sur leur cône de déjection -cela, avant même les travaux menés par le service de Restauration des Terrains en Montagne-, les modalités de la rétraction de la zone d’emprise des torrents diffèrent d’un torrent à l’autre. Par ailleurs, la spécificité de chaque organisme se retrouve aussi dans la morphologie des cônes de déjection qui influence notablement la dangerosité des torrents.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

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Shifting Lands. New insights into periglacial geomorphology

6e Journée des Jeunes Géomorphologues DYNAMIQUES MORPHO-SÉDIMENTAIRES ACTUELLES D’UNE RIVIÈRE FORTEMENT AMÉNAGÉE : LE CAS DE LA BASSE DURANCE. Emmanuel RIBES1* Direction de thèse : Mireille PROVANSAL1*, Claude PARRON2* Université d’Aix-Marseille I, UFR des Sciences Géographiques et de l’Aménagement Université d’Aix-Marseille III, * Centre Européen de Recherche et d’Enseignement des Géosciences de l’Environnement, UMR 6635 CNRS 1 2

La Durance, affluent alpin du Rhône, est le parfait exemple d’une rivière torrentielle dont la dynamique morpho-sédimentaire fut radicalement transformée au cours du siècle dernier par l’action anthropique en particulier (déprise agro-pastorale, travaux RTM, aménagements hydro-électriques, extractions…).

Les réajustements géomorphologiques de la Durance ont fait l’objet d’études, pour partie déjà anciennes ou sommaires (PIERI, 1983; JURAMY et MONFORT, 1986; MIRAMONT, 1998; EDF, 2000; WARNER, 2000 ; SOGREAH, 2001). A la demande du Syndicat Mixte d’Aménagement de la Vallée de la Durance, le sujet de thèse propose donc une étude réactualisée du fonctionnement de la rivière dans son cours aval, qui connaît une augmentation des apports hydro-sédimentaires depuis 10 ans.

Après une description détaillée de l’évolution géomorphologique du lit mineur au cours des 50 dernières années, l’étude fait le point sur sa dynamique actuelle en examinant le rôle de l’action d’EDF (retenues, restitutions) et des crues sur le transport solide. Bien que 114

les restitutions EDF réinjectent massivement des limons dans un secteur qui n’est plus réalimenté en sédiments grossiers depuis les aménagements, les mesures de terrain démontrent qu’elles contribuent parallèlement à la réactivation de la dynamique de la bande active et du charriage de manière notable.

L’analyse de données EDF et expérimentales sur le transport en suspension montre par ailleurs l’apport mineur des restitutions comparativement aux crues qui véhiculent actuellement 90% des MES. Entre 1994 et 2004, le passage des crues dans le lit mineur réduit de la basse Durance a également réactivé des érosions latérales, mises en évidence par photo-interprétation et levés GPS, fournissant ainsi des volumes importants d’alluvions grossières à la rivière.

L’étude traite ensuite du contrôle exercé par la géométrie et la végétalisation du lit sur le transit sédimentaire. L’approche conjointe de relevés topo-bathymétriques, d’analyses sédimentaires, de modélisations de terrain (MNT) et hydrauliques (TELEMAC-2D), met en valeur le rôle important des souilles

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

d’extraction sur le piégeage des sédiments fins et l’inefficacité des chasses programmées pour leur évacuation. Le suivi topographique des dépôts du lit mineur permet enfin de quantifier le filtrage biologique et le rôle déterminant des essartements sur le transit des sédiments en période de crue.

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Shifting Lands. New insights into periglacial geomorphology

6e Journée des Jeunes Géomorphologues LES MORPHOLOGIES SOUS-MARINES,TÉMOINS DES VARIATIONS EUSTATIQUES DEPUIS LE PLÉISTOCÈNE, DANS LES ATOLLS DE L’ARCHIPEL DES MALDIVES. Caroline RUFIN Laboratoire Géomer LETG UMR 6554 CNRS – IUEM Technopôle Brest-Iroise, 29280 Plouzané.

L’archipel des Maldives, né d’un point chaud, a subi une évolution complexe. L’analyse des structures atolliennes par emboîtement d’échelle (méga-atoll, pseudo-méga atoll, atoll de premier ordre, faru, thila…) laisse envisager une organisation complexe entre subsidence et eustatisme et permet de considérer des scénarii variés dans l’évolution de l’archipel.

L’observation de formes atolliennes subimmergées, par photo-interprétation, et immergées, par plongées en scaphandre autonome, permet de repérer des héritages karstiques. Des morphologies sous-marines de type encoches ou grottes, suggèrent une évolution non linéaire du niveau de la mer lors de la remontée postglaciaire. Ces repères observés à des profondeurs oscillant entre – 55 m et – 5 m, suivant six niveaux distincts (- 11 m, - 17 m, - 25 m, - 35 m, - 45 m, - 55 m), correspondent à des replats identifiés sous diverses latitudes. La conservation de ces témoins nous laisse envisager une submersion rapide holocène, même si nous n’excluons pas que certains d’entre eux correspondent à des formes régressives. Cet échelonnement de 116

paléorivages remet en question l’hypothèse d’une remontée régulière du niveau de la mer au cours de la transgression postglaciaire et plus particulièrement depuis 11,3 Ka (Meltwater pulse 1B) et suggère un caractère mondial de ces séquences bathymétriques.

L’occurrence de ces morphologies holocènes invite également à nous interroger sur les vitesses d’érosion dans l’élaboration des encoches marines.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

6e Journée des Jeunes Géomorphologues L’ÉVOLUTION MORPHOGÉNIQUE DES FALAISES BASALTIQUES DE LA GRANDE ÎLE D’HAWAÏ Guillaume MARIE Laboratoire Géomer LETG UMR 6554 CNRS – IUEM Technopôle Brest-Iroise, 29280 Plouzané

Les rivages de l’île volcanique d’Hawaï offrent une diversité de paysages liés à la durée d’évolution des abrupts côtiers. L’observation des formes a permis de dégager différents processus élémentaires et des systèmes morphogéniques plus complexes à l’origine du recul des falaises.

L’abrupt côtier est soumis à l’influence croisée de la gravité, des coups de boutoir des vagues et, dans le cas des deltas de lave encore mal stabilisés, de glissements au sein du soubassement de débris hydroclastiques.

Le diaclasage de la roche facilite l’éboulement de la paroi, processus le plus fréquent sur la plupart des littoraux basaltiques. Si l’appel au vide intervient souvent dans la chute, il est négligeable pour les falaises les plus basses qui sont littéralement démantelées par l’alternance de pressions et de succions des vagues déferlantes. Les basculements de pans de falaise sont caractéristiques des coulées de lave les plus récentes, de quelques années à plusieurs centaines d’années. Des fractures de distension, parallèles au trait de côte, s’ouvrent sur la plate-forme sommitale.

Une fois le bloc tombé, une nouvelle ligne de discontinuité se crée, prélude à une nouvelle phase de lent basculement. L’abrasion à la base des escarpements façonne parfois des encoches, notamment dans les terrains les plus récents ou dans les brèches basales des coulées aa. Un effondrement est alors susceptible de se produire. Sur le long terme, les glissements de terrain sont plus fréquents en raison d’une roche plus sensible aux infiltrations d’eau de par son état d’altération.

Outre ce retrait simple des falaises, fait de chutes localisées de masses rocheuses, deux systèmes plus complexes, et courants sur les littoraux basaltiques lorsque les conditions structurales sont favorables, ont été mis en évidence. D’une part, des grottes marines adjacentes sont creusées à la base des falaises hautes de plusieurs mètres. Leurs reculs individualisent des promontoires dont l’assise est à son tour attaquée, formant des arches littorales. Après l’effondrement de la voûte des arches, le pinacle rocheux qui subsiste en avant de la falaise est progressivement détruit. Cette évolution est typique des coulées de quelques 117

Shifting Lands. New insights into periglacial geomorphology

années à plusieurs centaines d’années. Elle engendre l’irrégularisation longitudinale du trait de côte avant sa simplification.

D’autre part, le délogement latéral de blocs sur la falaise façonne parfois des gradins qui s’organisent en escalier. Ce mécanisme est surtout observable dans les secteurs les moins exposés aux vagues et au débouché de gorges étroites perpendiculaires à la ligne de rivage, formant un amphithéâtre.

En raison de l’élévation du niveau relatif de la mer sur l’île d’Hawaï, consécutive à sa subsidence volcano-isostasique, les platesformes d’érosion marine sont rarement observables. Le recul de certaines portions de falaise, taillées dans des coulées de quelques dizaines à quelques centaines d’années, façonne néanmoins progressivement une banquette d’érosion marine de haute mer, fortement contrôlée par la structure de la roche, généralement 0,5 à 1 m au-dessus du niveau moyen de la mer, soit la position d’attaque maximale des vagues lors des tempêtes ordinaires (annuelles). Elle prouve, s’il en était besoin, l’efficacité morphogénique supérieure des vagues lors d’événements tempétueux, par rapport à leur action continue et au même niveau en dehors de ces épisodes. Des gradins de tempête, en partie structuraux et placés plus haut sur l’abrupt côtier, témoignent de l’action morphogénique des événements paroxysmaux.

La quantification des rythmes, bien qu’imparfaite et pleine d’approximations, montre une tendance générale à la diminution des vitesses de recul des abrupts côtiers.

L’érosion rapide, qui peut dépasser 100 m la première année d’existence des deltas de lave, diminue rapidement au fur et à mesure de la stabilisation de leur assise de débris.

Lorsque les agents marins et la gravité sont 118

les seuls à intervenir, le temps de retour des épisodes de recul semble varier, pendant une centaine d’années, entre quelques mois et une dizaine d’années. La récurrence des épisodes est ensuite généralement plus espacée, de l’ordre de plusieurs décennies à plusieurs siècles, parfois moins, lorsque le matériel est plus sensible à l’érosion. Cette décroissance du rythme de recul permet progressivement la genèse et la conservation de taffonis et de nids d’abeilles sur l’abrupt côtier, formes d’alvéolisation fréquentes et particulièrement remarquables sur les littoraux basaltiques.

European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

6e Journée des Jeunes Géomorphologues EVOLUTION HISTORIQUE ET RECONSTITUTION DE LA DYNAMIQUE D’UN PALÉOFLEUVE SUR UNE PLAINE COTIÈRE SUBSIDENTE. EXEMPLE DE LA “NATISO” SUR LE SITE DU PORT FLUVIAL D’AQUILÉE (VÉNÉTIE JULIENNE, ITALIE DU NORD).

Isabelle SICHE Doctorante, Equipe « Dynamique des Milieux et des Risques » (DYNMIRIS) UMR 8586 CNRS-PRODIG Université Paris VII Denis Diderot 2, place Jussieu, CC 7001 75251 PARIS CEDEX 05 Isabelle.siche@cicrp.jussieu.fr

La dynamique et la morphologie d’un fleuve sur sa plaine côtière sont profondément influencées par l’évolution du niveau de base.

Aquilée, second port fluvial romain de l’Italie, était bâtie sur les rives du Natiso à l’apex d’un delta construit par un organisme fluvial plus important : l’Isonzo. Le site n’est aujourd’hui traversé que par un modeste cours d’eau de résurgence qui vient se jeter dans une lagune et le Natiso est devenu un affluent de l’Isonzo.

Sa capture s’inscrit dans l’évolution générale du réseau hydrographique qui se déplace vers l’est par défluviations successives, laissant les lobes deltaïques abandonnés se transformer en lagune. Or à ce jour nous ne connaissons ni les causes exactes, ni la chronologie, ni les modalités de la capture de la Natiso et de la configuration de l’ensemble du réseau fluvial sur la période historique, qui aurait été un des facteurs de l’abandon du port. La reconstitution du paléo-réseau a nécessité le croisement des données topographiques, géologiques, géophysiques et archéologiques. En effet,

les divagations successives des cours d’eau et la profonde anthropisation ont largement effacé les reliefs résiduels. L’élaboration d’un MNT, avec des isohypses équidistantes de 0,5 à 1 m, est le seul moyen de percevoir la micro-topographie de la plaine alluviale et d’extraire des vallées abandonnées. La photointerprétation de clichés aériens couleurs, ensuite comparée à une image LandSat TM, a permis de reconstituer des tracés probables et, par endroits, la morphologie du chenal.

Enfin, l’analyse des minéraux lourds a pu nous donner des indications sur la provenance des sédiments et donc de l’origine du cours d’eau L’identification de ces paléo-vallées, confrontée à la répartition des restes archéologiques, indiquerait que l’Isonzo, aurait eu un tracé séparé de celui du Natiso, et que son embouchure se trouvait déjà très à l’est du delta dès l’époque romaine.

L’analyse morpho-sédimentaire de carottages profonds sur le chenal portuaire et l’analyse de la microfaune confirment l’existence d’un 119

Shifting Lands. New insights into periglacial geomorphology

paléo-chenal romain de forte énergie laissant place à une séquence granulométrique dégressive en milieu saumâtre à partir du IVè siècle, lorsque le port perdit son activité. La dynamique fluviale a ensuite été précisée par des critères de compétence et de puissance spécifique et les sections fluviales transversales à partir de sondages tomographiques, qui permettent la reconstitution de l’étendue et de l’épaisseur des formations alluviales.

La remontée relative du niveau moyen de la mer aurait donc joué un rôle important puisque la perte de compétence et de capacité accompagne la remontée du coin salé due aux variations eustatiques et au tassement des dépôts deltaïques. Le relèvement du niveau de base du Natiso aurait forcé ainsi le dépôt des fines et engendré une défluviation du Natiso dans l’Isonzo. Le colmatage consécutif du chenal fut favorisé par l’abandon du port après les invasions d’Attila en 452 ap JC. Mots-clefs : hydrogéomorphologie, paléochenaux, reconstruction paléo-environnementale, paléo-hydrologie

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

6e Journée des Jeunes Géomorphologues L’ÉVOLUTION DES VALLÉES DE LA MEURTHE ET DE LA MOSELLE DANS LE BASSIN PARISIEN ET LE MASSIF SCHISTEUX RHÉNAN DEPUIS LE PLÉISTOCÈNE MOYEN : PREMIERS RÉSULTATS. Stéphane CORDIER Laboratoire Géodynamique des milieux naturels et de l’environnement, Département de Géographie, Université Paris XII Val de Marne, 61, avenue du Général de Gaulle, 94010 Créteil Cedex. s-cordier@club-internet.fr

Les études menées depuis plusieurs années dans la vallée de la “Paléo-Meurthe-Moselle” (vallée de la Meurthe, et vallée de la Moselle en aval de la confluence avec la Meurthe), en aval du Massif vosgien, ont abouti à la reconnaissance de huit niveaux de basses et moyennes terrasses (niveaux PMM8 à PMM1), dont les planchers d’incision sont étagés entre 90 et 5 m d’altitude relative audessus du bed-rock du fond de vallée (PMM0).

Ces niveaux sont associés à des formations alluviales (F) plus ou moins préservées.

La capture de la Haute-Moselle par la PaléoMeurthe (datée par thermoluminescence dans la vallée de la Meuse aux Pays-Bas et par U/ Th sur spéléothèmes dans celle de la HauteMoselle sur le site de capture) est intervenue à la fin de la mise en place de F-PMM4 (formation située à 30 m d’altitude relative), il y a 250-270 ka. Les formations F-PMM8 à F-PMM5 (et l’essentiel de F-PMM4) sont donc surtout composées d’alluvions issues des

assises gréso-conglomératiques du PermoTrias, largement développées dans le bassin de la Meurthe.

Les formations plus récentes F-PMM3 à FPMM0 sont post-capture, comme en témoigne la présence de nombreux éléments cristallins issus du bassin supérieur de la Moselle, développé dans le socle du Massif vosgien.

Ces formations ont été datées par OSL et 14C : elles correspondent à une nappe saalienne (F-PMM3, située vers 20 m d’altitude relative, mise en place durant le stade isotopique 6), et à deux nappes weichséliennes (F-PMM2, à +10 m, mise en place lors du Pléniglaciaire inférieur et moyen, et F-PMM1, à +5 m rapportée au Pléniglaciaire supérieur), le remplissage de fond de vallée F-PMM0 étant daté du Tardiglaciaire et de l’Holocène.

Les études sédimentologiques et les datations relatives aux formations F-PMM4 à F-PMM1, pour lesquelles on dispose de 121

Shifting Lands. New insights into periglacial geomorphology

nombreuses coupes, soulignent le caractère cyclique de l’alluvionnement depuis le Saalien, en rapport avec les pulsations glaciaires affectant le Massif vosgien (bassin supérieur de la Moselle, et dans une moindre mesure de la Meurthe) : la sédimentation s’effectue essentiellement durant les phases pléniglaciaires et tardiglaciaires du cycle, avec en général une phase d’érosion mineure entre les deux (ravinement des dépôts pléniglaciaires). La sédimentation semble se poursuivre lors du retour de conditions climatiques plus tempérées, avec la mise en place d’une couverture limoneuse. La phase majeure d’incision du bed-rock intervient lors de la réapparition de conditions périglaciaires.

L’extension des glaciers dans le Massif vosgien et leur évolution influencent également la granularité et la lithologie des alluvions : à l’aval immédiat du massif, les alluvions pléniglaciaires de la Meurthe sont sableuses et issues du Permo-Trias, tandis que les alluvions tardiglaciaires sont plus grossières et plus riches en éléments cristallins issus du haut bassin. Ce granoclassement s’inverse rapidement vers l’aval, en raison des apports réalisés par les affluents de la Meurthe à dynamique périglaciaire. En aval de la confluence avec la Moselle, les formations post-capture témoignent généralement de deux décharges alluviales, l’une pléniglaciaire (alluvions apportés par la Meurthe), et l’autre tardiglaciaire (apports plus abondants provenant du bassin de la Haute-Moselle).

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European Science Foundation, SEDIFLUX network meeting #2, Clermont-Ferrand, France

6e Journée des Jeunes Géomorphologues RYTHME DE PROGRADATION DE LA PLAINE DE THESSALONIQUE À L’HOLOCÈNE (GRÈCE) – MÉTHODOLOGIE ET HYPOTHÈSES DE TRAVAIL. Matthieu GHILARDI Allocataire - Moniteur Université Paris 12 Val-de-Marne Ecole Pratique des Hautes Etudes lab. GEONAT EA 435 lab. PRODIG UMR 8586 lab. CNRS Meudon UMR 8591 06 10 26 08 64 matthieughilardi@wanadoo.fr

La plaine de Thessalonique se situe au nord de la Grèce en Macédoine Centrale. Cette plaine, résulte de la coalescence des deltas de quatre fleuves que sont l’Aliakmon, l’Axios, le Galikkos et le Loudias (ancien fleuve Moglenitsa). La création de la plus grande aire deltaïque de Grèce est récente et n’a pas plus de 3 000 ans.

Plusieurs auteurs anciens comme Strabon, Démosthène, Thucydide décrivent la région. À partir de ces témoignages historiques des historiens, au cours du XXe siècle, ont entrepris des reconstitutions paléogéographiques de la progradation de la plaine. Tous ces travaux ont pour point commun de tenter une reconstitution des différentes phases d’avancée du trait de côte au cours des 2 500 dernières années, en se basant sur les récits historiques et des cartes établies par les voyageurs du XIXe siècle, comme William Leake. Seul Bottema en 1974 a fondé sa démarche scientifique sur des forages et des études polliniques. En revanche,

sa reconstitution paléogéographique, n’exploitant pas les sources historiques, a très vite montré ses limites, et de nombreuses imprécisions cartographiques reflètent la difficulté d’interprétation des données. C’est d’ailleurs le principal défaut qui caractérise les cinq reconstitutions majeures de la plaine, élaborées par Struck en 1908, Hammond en 1970, Bottema en 1974, Bintliff en 1976 et Astaras en 1988.

Nous avons établi une méthodologie qui croise l’approche historique et paléoenvironnementale et qui vise à combler les lacunes des deux approches. Notre objectif est de préciser la chronologie de formation de la plaine de Thessalonique. À ce jour deux carottages ont déjà été réalisés, l’un à Trikala, le second à Méthone. Le premier est en cours d’analyse. Nous présentons notre méthodologie d’études et nos hypothèses de travail.

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