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4. Rock  avalanche   with  snow  ingesVon.   4  M  m3  water     equivalent  possible  


Apparent source  of  the  large  May  5,  2012  avalanche  on  Annapurna  IV  

©  J.S.  Kargel  


Apparent source  of  the  large  May  5,  2012  avalanche  on  Annapurna  IV  


©  J.S.  Kargel  


300 m  length  of  ridgeline  retreat   according  to  ETM+  

Apparent source  of   rock  avalanche  ~300     m  wide  X  1300  m  high     X  30  m  ridge  recession   ~  107  m3  (from  this  photo,     ETM+,  ASTER,  and     Google  Earth).     Mass  esVmate  ~  2.5-­‐3.0  X  107     tonnes  from  volume.  Compares  to  22  M  tons  given  by     David  Petley  from  seismic  energy  release  of  this  event.  


300 m  length  of  ridgeline  retreat   according  to  ETM+  

Apparent source  of   rock  avalanche  ~300     m  wide  X  1300  m  high     X  30  m  ridge  recession   ~  107  m3  (from  this  photo,     ETM+,  ASTER,  and     Google  Earth).     Mass  esVmate  ~  2.5-­‐3.0  X  107     tonnes  from  volume.  Compares  to  22  M  tons  given  by     David  Petley  from  seismic  energy  release  of  this  event.  


Picture of  Dust  Distribu<ons  


Dust over  vegeta<on    


Dust on  fallen  trees  and  on  gorge  


1-­‐5 cm  of  fine  dust  covers  most  of  the  upper  Se<  Basin  


Rockfall path  towards  to  Gorge  


Rockfall path  towards  to  Gorge……  


Rockfall path  towards  to  Gorge……  


Rockfall path  towards  to  Gorge……  


e. Working  hypothesis  #2:  All-­‐of-­‐the-­‐ above  (mulCple  sources).     •  A  composite  model  might  work  best.     •  water  produced  by  fric<onal  mel<ng  of   avalanche  snow  and  ice,  and  water  stored  in  the   rockfall-­‐dammed  gorge  lake  and  perhaps  in  karst   each  might  have  contributed  to  the  flood.       •  The  process-­‐chain  of  mass  movements  then  was   triggered  by  the  large  avalanche/landslide.      


5. Immense  dust  cloud,  air  fall  deposiVon     and  intense  avalanche/slope  winds  


6.  Water  derived  from:   -­‐-­‐  Wet  snow     -­‐-­‐  Supraglacial  melt  water   -­‐-­‐  Avalanche  melt  water   -­‐-­‐  Then  added  to  impounded   water  in  gorge  


7. Hyperconcentrated     slurry  outburst  flood  


Canyoning and  measurement  of  Gorge  


Canyoning and  measurement  of  Gorge   Gorge  depth  is  not  uniform   and  it  is  esVmated  between   200  m  to  600  m  

Gorge width  ranges  between   50  to  150  m  width  


Hovering and  taking  video  inside  the  gorge  

Pictures taken  by  :  Stephanie  Spray  


Damming ,  materials  and  topography  


Gorge topography   h  

s to m e e s   f e eli Upper  r

ou t s e h t   s ward o t   g n i s  go a   e n i l c tly  de h g i l s   e  b

Poten<al water  damming  limit  

Base of  the  Gorge  is  almost  horizontal,  which  provides  berer   space  for  the  accumula<on  of  water  within  it.      


Avalanche and  rock  fall  on  May  5  2012  

People noVced  the  change  in  hydrology  

Damming few  weeks  before  flood  

Accumulated water  several  M  m^3  


Concluding Remarks   •  Rock  slide  dam  and  accumula<on  of  water  in  the  gorge   has  resulted  in  the  forma<on  of  a  natural  reservoir   before  the  avalanche  event  (approx.  three  weeks   before  May  5th.)   •  Avalanche  of  rock  and  ice  and  the  large  supply  of   unconsolidated  ancient  lake  sediments  in  the  gorge   created  the  pressure  and  resulted  on  the  outburst  of   the  natural  reservoir.   •  Need  to  iden<fy  the  most  suitable  alarming  system  to   minimize  the  loses  from  such  events  


The city  of  Pokhara  was  built  on  deposits  from  such   floods,  including  50-­‐60  m  of  debris  from  one  flood   only  450  years  ago.  


Vulnerable community  on  the  SeV  River  floodplain  


What Else  we  Did  ?   Detailed   geological   Mapping  

Flood InundaVon   Mapping  

Socio economic   survey  

Early warning   System  

Dhananjay Regmi: Seti River disaster and hazards facing Pokhara, Nepal part 2 of 3  

Slides for presentation given to High Mountains Adaptation Partnership in Huaraz, Peru on 13 July 2013.

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