Nepal's quake-driven landslide hazards
Large earthquakes can trigger dangerous landslides across a wide geographic region. The 2015
M
w
7.8 Gorhka earthquake near Kathmandu, Nepal, was no exception. Kargal
et al.
used remote observations to compile a massive catalog of triggered debris flows. The satellite-based observations came from a rapid response team assisting the disaster relief effort. Schwanghart
et al.
show that Kathmandu escaped the historically catastrophic landslides associated with earthquakes in 1100, 1255, and 1344 C.E. near Nepal's second largest city, Pokhara. These two studies underscore the importance of determining slope stability in mountainous, earthquake-prone regions.
Science
, this issue p.
10.1126/science.aac8353
; see also p.
147
Lake Shewa in northeastern Badakhshan, Afghanistan, was dammed sometime in antiquity when a large rock avalanche (sturzstrom) from the faultshattered and strongly weathered Archean gneisses of the Zirnokh peaks to the north moved into the Arakht River valley. This rock avalanche dammed up the river and its tributaries to a dam thickness of c. 400 m, producing a 12-km-long lake that is as much as 270 m deep, leaving c. 80 m of freeboard to the top of the dam. At least four separate instances of slope failure have been mapped at the site of the landslide dam, as well as a rock glacier, using remotely sensed data, historical maps, and Google Earth™. Spring seepage through the dam face has caused several recent subsidiary debris slides, which if continued at a large enough scale for long enough, or with additional seismicity from the active strike-slip faults that cross beneath the landslide dam, could threaten its integrity. Otherwise the clean water that emerges from the dam face could be the source of an unvarying mini-hydroelectric power source, in addition to the agricultural irrigation that it provides at the present time.
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