Island View Beach Natural Environment Presentation Natural History

How did we get here?

NATURAL HISTORY

The distant and not so distant natural history of Island View Beach Updated: April 9, 2015

The Dune/Beach/Spit Complex

Natural History

The key points cover in this section are: Nature is dynamic and landscapes are always changing – sometimes quickly - sometimes more slowly Island View Beach is a dynamic system dating back at least 15,000 years Modification of the land for agriculture and infrastructure has resulted in changes to local hydrology, and vegetation patterns

Fraser Glaciation

https://earthdata.nasa.gov/

Fraser Glaciation Nature is dynamic and landscapes are always changing – sometimes quickly and sometimes more slowly.

The last glacial maximum wiped the slate clean on our local landscape. So, this is a good place to start.

This image depicts what you would have seen at Island View Beach about 15,000 years ago, when almost the entire region was covered with a kilometre thick sheet of ice and snow.

Glacial Effects

Luis María Benítez - public domain

Glacial Effects Almost 100 tons per square foot of ice was bearing down on the landscape at Island View Beach.

Under this stress the earth’s crust can change shape. At the same time, the liquid volume of the sea decreases as more water is taken up in ice.

This results in a wide variation on local conditions based on rising and falling sea levels combined with the rising, falling and stretching of the earth’s crust.

Island View Beach Elevation Relative to Sea Level

Fraser Glaciation

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2

Adapted from Shugar et al. 2014

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Island View Beach Elevation Relative to Sea Level

This graph shows the years before present at the bottom and elevation above or below current sea level (0) at the side.

1. The red line shows your position if you were standing on Island View Beach in the past.

2. The ice retreated rapidly and almost the entire Saanich Peninsula was 75 m below sea level about 14,000 years ago.

3. As the weight of all that ice was removed, the earth’s crust rebounded and sea level was 30 to 50 m below current levels about 11,000 years ago.

4. Sea level rose up very rapidly and stabilized about 2000 years ago at close to the current level. However, in the past 150 years, sea levels have been rising around the world.

Shugar Dan H., Ian J.Walker, Olav B. Lian, Jordan B.R. Eamer, Christina Neudorf, Duncan McLaren, Daryl Fedje. 2014. Post-glacial sea-level change along the Pacific coast of North America. Quaternary Science Reviews 97 (2014) 170-192.

Modern Sea Level Change

22 cm

16 cm

http://www.epa.gov/climatechange/science/indicators/oceans/sea-level.html

Modern Sea Level Change In the past 138 years in this graph, global sea level has been rising. This orange line shows an increase of 22 cm in absolute sea level for the world’s oceans. About 16 cm in rise since 1930 indicates an increasing rate in recent years.

Site specific relative sea level rise is complicated to predict. A considerable amount of work is underway in the region to better understand implications of sea level rise. This will greatly affect the management of low lying coastal sites like Island View Beach Regional Park.

http://www.epa.gov/climatechange/science/indicators/oceans/sea-level.html

Soil Profile From the Shoreline Gravel

Sand Sand/Pebble

Clay/Silt

Bobrowsky and Clague, 1991

Soil Profile From the Shoreline Geologists reconstructed a 14 m soil profile from drill cores at the park shoreline.

The Pleistocene sediments originate at Cowichan Head where they were laid down before 29,000 years ago.

The spit is made up predominantly of coarse sand and gravel sediments laid down in a lengthy period of intertidal and perhaps shallow subtidal sedimentation over the past 10,000 years.

The active surface is sandy and is underlain by layers of gravel and sand.

Layers of fine sediment (silt and clay) indicate periods of calm conditions or inundation by seawater, whereas coarser gravel beds record episodic stormy periods.

NEOTECTONIC INVESTIGATIONS ON VANCOUVER ISLAND (9:!B, F). 1991. P.T. Bobrowsky, B.C. Geological Survey Branch; J.J. Clague, Geological Survey of Canada.

Bennett, K., Bobrowsky, P., Clague, J., Huntley, D. (n.d.) Surficial geology and geomorphology of Central Saanich Peninsula, southeastern Vancouver island.

Municipality of Central Saanich Resource Atlas.

Soil Profile From the Upland (wetland and old fields) Present day Peat (Terrestrial) Marine/estuarine mud Ancient Peat (Terrestrial) 2,400-2,600 years ago Ancient marine shoreline more than 2,600 years ago

Bobrowsky and Clague, 1991

Soil Profile From the Upland (wetland and old fields) Soil profiles were also created from the backshore between the beach and the forested bluffs to the west. The ancient shoreline of muddy sands and gravels predates 2,600 years ago.

The layer found above represents a period of terrestrial soil development (wetland/peat bog) where organic materials have been aged to bracket a period of approximately 2,400 to 2,600 years ago.

The overlying mud layer contains remnants of marine organisms suggesting flooding of this low lying area around 2,400 years ago as sea levels rose and stabilized. This could be indicative of an active salt water lagoon or marsh complex through most of this period of stable sea levels.

The thin organic layer on top represents the present day terrestrial soils overlying the marine muds. There are no carbon dates for this material but by its depth, it would appear to be quite recent.

NEOTECTONIC INVESTIGATIONS ON VANCOUVER ISLAND (9:!B, F). 1991. P.T. Bobrowsky, B.C. Geological Survey Branch; J.J. Clague, Geological Survey of Canada

Ancient Forest

Photo: Audrey Dallimore

Ancient Forest These images describe what appears to be an ancient drowned forest in the intertidal zone of Island View Beach. This feature can be observed best during the winter season at lower tides.

This feature suggests that Island View Beach experienced what is known as a co-seismic subsidence event 1200 to 1800 years ago. As the land subsided, the marine transgression was so rapid that forest soils and debris remained essentially intact and can be observed in the modern day sediments eroding from the beach.

This could be linked to the marine sediments we see overlying peat in the backshore areas that was illustrated in the last slide.

Personal Communication: Audrey Dallimore, PhD; Associate Professor; Royal Roads University (250) (391-2580) and Visiting Scientist at Geological Survey of Canada- Pacific; 9860 West Saanich Road, Sidney, B.C. V8L 4B2

Aerial Photography 1930

Island View Beach Regional Park (green boundary) is within the larger study area (red boundary)

Randhawa, Gendall and Webb, 2012

Aerial Photography 1930 Starting in 1930 we can look at the evolving landscape from repeated aerial photographs.

Photos were compiled for a project at Camosun College to look at changing land use patterns.

The red boundary is the study area. The green boundary is the regional park.

1930 - A mosaic of open sand dunes, wetlands and low shrubs or meadow habitats is evident in the park. Ditches were established on Tsawout lands north of Island View Beach Regional Park. These were constructed during World War 1. Properties are separated by fence lines.

Randhawa, G. J. Gendall, J. Webb. 2012. Historical and Successional Baseline Study of Island View Beach: A summary of the historical land-use and aerial photograph analysis since the 1930s. Unpublished manuscript for Camosun College Environmental Technology Program. 39 pp.

Aerial Photography Change Detection 1930-2011

Randhawa, Gendall and Webb, 2012

Aerial Photography Change Detection 1930-2011 When you consider the land cover on the study area from 1930 to 2011 there are some considerable changes.

Researchers outlined the extent of woody vegetation and infrastructure development throughout several periods up to 2011.

Since 1930, low lying wetland habitats have diminished by almost three quarters.

The researchers suggest that lower water levels have resulted in forest and shrub cover more than doubling in extent.

Infrastructure now occupies almost 6% of the landscape.

Randhawa, G. J. Gendall, J. Webb. 2012. Historical and Successional Baseline Study of Island View Beach: A summary of the historical land-use and aerial photograph analysis since the 1930s. Unpublished manuscript for Camosun College Environmental Technology Program. 39 pp.

Natural History Summary Island View Beach has been evolving for at least 15,000 years.

It is a system that continues to change.

The land is composed primarily of sands and gravels.

Modification of the land has resulted in changes to local hydrology and vegetation.