4 August 2014
Over the last few days there have been several developments in the Sunkoshi landslide crisis, some positive and some less so. The very high direct cost of the landslide is now becoming clear. Whilst only 18 bodies have been recovered to date, the number missing is thought to be about 155, making this the most costly landslide in Nepal for many years. The magnitude of the losses reflect the scale of the landslide – Kunda Dixit very kindly sent a set of images of the Sunkoshi landslide collected by the Nepal Army to me, including this overview of the site:
The landslide is reported to be about 45m high at the highest point and 25 m at the lowest. It overtopped late on Saturday, fortunately without a breach to date, and reports suggest that the level of the lake is falling slowly. This is of course the ideal outcome, but great care is needed. If the lake level is falling then water must either be seeping through the dam or the spillway is eroding, either of which can accelerate to generate a rapid release event. Thus, there continues to be a need to manage the hazard very carefully and the ensure that areas downstream are not reoccupied.
The response of the Nepali authorities does appear to have been admirably quick and decisive, from the early action to open drainage to the large-scale evacuations downstream. It is notable that according to reports they have made use of the very high level of technical skill on landslides within in the country, which has not always been the case elsewhere.
There has been some discussion in the media of the causes of the landslide. In an article today, Narendra Raj Khanal from Tribhuvan University suggested that this slope developed some instability last year. This would be consistent with the progressive development of the landslide, which is clear from the very good Google Earth imagery of the site. This is an image from 2009, as a perspective view:
And this is an image from 2012:
The deterioration in the state of the middle part of the hill (around the area with the location marker) is very clearly visible between the two images. Presumably this became much worse last year.
Finally, it is important to remember that this landslide will be having devastating impacts upstream as well. Clearly the Arniko Highway is closed, and will remain so for some days to come. This is the only road to Tibet from Nepal, and of course the time period each year in which it can be used is comparatively short anyway. Those living upstream will now be isolated from the rest of the country, and of course the lake has inundated a large area of road. Kapil Dhital is a civil engineer who was at Bharabise at the time of the landslide. He has tweeted a series of photographs of the landslide and lake, including this one showing a now submerged dwelling: