ISS001-E-6765.JPG, http://eol.jsc.nasa.gov/DatabaseImages/EFS/highres/ISS001/ISS001-E-6765.JPG
Big Surprises from the Nepal Gorkha Earthquakes
• The highest parts of the Himalaya lost elevation, while
the lower mountains and basins to the south were
uplifted.
• Landslides occurred in a peculiar pattern.
• Number of landslides was far less than in other similarly
powerful earthquakes.
• Glacial lakes sustained very little damage, contrary to
expectations.
• While the earthquakes caused large loss of life and
devastated some remote Himalayan valleys, the damage
could have been far worse.
Purple dots:
Earthquake-related
landslides
Red circles:
epi-centers of two
Largest shocks
COLOR SCALE:
Vertical uplift (red) or
downdrop (blue)
in meters from
ALOS-2 radar data
+1.13
- 0.82
Langtang village, 2012 (pre-earthquake)
Photo by David Breashears (GlacierWorks), by permission
Langtang village, 2015 (post-earthquake)
Photo by David Breashears (GlacierWorks), by permission
Tsho (Lake) Rolpa, one of Nepal’s most dangerous glacial lakes
Photo by Brian Collins (USGS)
Outlet of Tsho Rolpa with artificial lake lowering for outburst flood mitigation.
Photo by Brian Collins (USGS) shows cracks probably generated by the earthquake.
Conclusions
• 4,312 earthquake-related landslides mapped in Nepal
and adjoining Tibet
• Far fewer landslides than caused by earthquakes of
similar magnitude elsewhere.
• Some landslides, e.g., at Langtang, were terribly tragic.
• There could have been many disasters on the scale of
Langtang Valley, but reduced landslide numbers helped
many valleys, despite widespread serious damage.
• Reasons for reduced number of landslides are an area
of ongoing research; possibilities include high rock
strength and the earthquake’s unusually gentle shaking
at the surface.
• Damage at glacial lakes was also less than expected,
possibly due to the way the earthquake’s seismic waves
interacted with the rugged topography.