Geomorphic changes induced by the April-May 2015 earthquake sequence in the Pharak-Khumbu area (Nepal)

International audienceLandsliding is a common process shaping mountain slopes. There are various potential landslide triggers (rainfall, bank erosion, earthquakes) and their effectiveness depends on their distribution, frequency and magnitude. In a Himalayan context, the effects of monsoon rainfall can be assessed every year whereas the unpredictability and low frequency of large earthquakes make their role in triggering slope instability more obscure.Here we present field observations carried out in the Pharak-Khumbu area (East Nepal, Dudh Kosi catchment)before and after the April-May 2015 earthquakes. The limited size and shallow depth of the newly generated slope failures are noteworthy. More generally, these geomorphic changes and their characteristics maybe explained by the nature of the 2015 climate: while the 2014-2015 winter was unusually dry, snowfalls and rainfalls were abundant during March and April, hence increasing the pore pressure and the potential instabilityof slopes and/or snow cover. Conversely, the rather weak monsoon rainfall of the 2015 summer did not takeadvantage of the many cracks opened by seismic shaking. Yet this may leave only a short delay for large landslidedevelopment during the next monsoon season