In an April 28th news item from Mountain Hidrology we can see a comparison of aerial photos of the before and after of the terrible avalanche in Langtang.
The earthquake of 25 April has presumably triggered a large avalanche / landslide which has buried the Langtang village under debris. On 25 April during the earthquake a helicopter of Simrik air was on its way to Langtang and Jason Laing on board of the helicopter made a picture of Langtang village complete covered under debris (Annapurna Post article). Using high resolution imagery of DigitalGlobe from before the earthquake we tried and identified the shape of the fields visible and numbered in the picture and on the map.
Langtang village was located below a very steep ridge and above the ridge there is a glacier towards the north-west and large snow field right above the village. There has been a lot of snow fall this year and at the moment of the earthquake there were considerable amounts of snow at higher altitudes. From a preliminary investigation we think it is most likely that either a snow avalanche from directly north of Langtang village or a debris/ice avalanche from the north-west has caused this disaster. These are marked by red arrows in the map.
We can see in this other image too:
Once post-earthquake imagery becomes available, we will be able to confirm the cause and detect further river blocking in the valley which may cause large lakes to form and could be a potential threat for the future.
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To have look at post-earthquake satellite imagery from NASA check this follow-up post:
The magnitude 7.8 Gorkha earthquake that struck Nepal on April 25, 2015, caused extensive damage in Kathmandu Valley and severely affected Nepal’s rural areas. The Langtang Valley in the Rasuwa district was particularly hard hit, as became apparent after pictures taken by a rescue helicopter mission on April 26 (Mountain hidrology). Numerous tourists and Nepali were, or are still trapped in the valley as road access is completely blocked by avalanches and landslides. The valley’s main village, Langtang , was completely destroyed by the earthquake, including a large, wet, debris- and ice-rich avalanche that has caused an unknown number of casualties. Other avalanches also struck elsewhere in the valley.
Space agencies around the world are providing extensive resources in a huge international effort. They are tasking their satellites to observe the areas hit by the earthquake, beginning immediately after the disaster in Nepal took place. Imaging initially focused on Kathmandu. Following the first social media reporting of the helicopter pilot’s comments, an emergency NASA-USGS-interagency Earthquake Response Team alerted satellite mission operations teams about the likely serious plight of Langtang and other Himalayan valleys. Advisories were also delivered to Nepal officials. The first relief missions arrived in the Langtang Valley about April 28.
United States Geological Survey/NASA Landsat-8 satellite observations were initially obscured by clouds, but on April 30, Landsat 8 acquired the first largely cloud-free image of the Langtang Valley. Scientists Walter Immerzeel and Philip Kraaijenbrink, both affiliated to Utrecht University in the Netherlands (and Immerzeel also with the International Centre of Integrated Mountain Development in Kathmandu), analyzed the imagery and compared it with pre-earthquake imagery from a year earlier. Their analyses revealed the true extent of the disaster that took place in the Langtang Valley. Langtang village was completely buried by a very large avalanche that originated from the glacier and snowfields on the northwestern slopes above the village. Large landslides or avalanches are also observed near the villages of Chyamki, Gumba, Mundu and Sindum. The avalanches reach to the margins of those villages. The extent of the damage around these small settlements will require further investigation using higher resolution imagery to be obtained from satellites, and word from relief crews on the ground. The area around Kyanjin Gompa seems to be relatively intact. The river at the Langtang village avalanche appears to be blocked, but there is no evidence yet of a lake forming behind the blockage. This may indicate that the water has found its way through the debris, snow and ice. The valley is vulnerable to secondary events such as mudslides and debris and ice avalanches; this situation could continue into the coming monsoon. will continue to monitor this situation closely using satellite data.
These scientists are part of an international volunteer group of 35 members led by University of Arizona scientists Jeffrey Kargel and Gregory Leonard, who launched the group soon after the earthquake occurred. This effort has been incorporated into the NASA-USGS-interagency Earthquake Response Team. Their goal is to systematically investigate the entire quake-affected area using remote sensing. Their results will support relief operations and identify secondary hazards, such as glacier lake outbursts, rivers blocked by landslides, and other unstable areas.
This is the first volunteer report of the project. If you want to see more about it you can go to the web page of this project: