Overnight a very large landslide occurred on the banks of the Sunkoshi River in northern Nepal.\u00a0 This landslide has created an instant, large-scale crisis as it has blocked the river.\u00a0 In Nepal the English language news media is excellent, so there is very good coverage of the event, helped also by the location of the landslide on the main road to Tibet, which facilitates access.\u00a0 The best gallery of images that I have seen is on the Nep Hub website<\/a>.\u00a0 This is the landslide from the slope above:<\/p>\n http:\/\/www.nephub.com\/latest-picture-of-sunkoshi-landslide\/<\/p><\/div>\n .<\/p>\n This is the lake that is building behind it:<\/p>\n http:\/\/www.nephub.com\/latest-picture-of-sunkoshi-landslide\/<\/p><\/div>\n .<\/p>\n And, from the Only Nepal website<\/a>, this is a view of the landslide from downstream:<\/p>\n http:\/\/www.onlynepali.net\/massive-landslide-blocks-sunkoshi-river-killing-6\/<\/p><\/div>\n .<\/p>\n The location of the landslide is 27.770 N, 85.870 E.\u00a0 The Google Earth imagery of the site is excellent:<\/p>\n .<\/p>\n My colleagues and I have been working in this valley on landslides for decade or so, and Katie Oven completed her PhD<\/a> on landslides in this area.\u00a0 On field trips up the valley we would often stop at Lamusangu to look at the debris flow deposits at this location, so a major landslide in this area is not a surprise. However, it is now a crisis.\u00a0 In the peak of monsoon season the river flow is high, and the images show that the lake is filling quickly.\u00a0 The images suggest that there is no reason to be confident that the dam will not breach rapidly when overtopped – indeed, quite the opposite I think as the length of the dam is not large and the materials appear to be fine grained.\u00a0 A breach now could generate a very large flood; when full the effects could be very serious.<\/p>\n Mitigation is of course to try to drain the lake whist evacuating everyone downstream.\u00a0 The valley is quite densely inhabited because of the road.\u00a0 A secondary hazard is that a major flood might destabilise the walls of the valley triggering further landslides downstream.\u00a0 Whilst the population can be protected with appropriate measures, which need to be implemented very fast, a dam breach flood has the potential to cause major damage.\u00a0 Given that this is the only road north out of Nepal, and the major strategic link to Tibet and China, the impacts on Nepal could be serious in the medium term.<\/p>\n So what to do? Well of course the first measure is to evacuate people downstream, and this has started<\/a>.\u00a0 The second is to put a warning system in place, probably at this stage consisting of an observation team with appropriate communications.\u00a0 The third will be to start to excavate a channel, which will require heavy machinery.<\/p>\n This is a very difficult problem to manage, so Nepal should seek international help.\u00a0 The best qualified people are the teams that dealt with the valley blocking landslide crisis<\/a> after the Wenchuan earthquake in China.\u00a0 Given the strategic importance of this road, the Chinese may want to help.\u00a0 However, time is very limited.<\/p>\n Ekantipur has tweeted<\/a> the follow image of the landslide:<\/p>\n![\"Sunkoshi\"](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2014\/08\/14_08-Sunkoshi-1-e1406963701792.jpg\")
<\/a>![\"Sunkoshi\"](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2014\/08\/14_08-Sunkoshi-2.jpg\")
<\/a>![\"Sunkoshi\"](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2014\/08\/14_08-Sunkoshi-3.jpg\")
<\/a>![\"Sunkoshi\"](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2014\/08\/14_08-Sunkoshi-4-e1406964300513.jpg\")
<\/a><\/p>\nUpdate<\/h5>\n
![\"Sunkoshi\"](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2014\/08\/14_08-Sunkoshi-5.jpg\")
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