{"id":44184,"date":"2023-07-14T05:54:49","date_gmt":"2023-07-14T05:54:49","guid":{"rendered":"https:\/\/blogs.agu.org\/landslideblog\/?p=44184"},"modified":"2023-07-14T05:55:38","modified_gmt":"2023-07-14T05:55:38","slug":"sabche-rockslide-1","status":"publish","type":"post","link":"https:\/\/blogs.agu.org\/landslideblog\/2023\/07\/14\/sabche-rockslide-1\/","title":{"rendered":"The Medieval 23 cubic kilometre Sabche rockslide in Annapurna, Nepal"},"content":{"rendered":"

The Medieval 23 cubic kilometre Sabche rockslide in Annapurna, Nepal<\/strong><\/h4>\n

A paper (Lav\u00e9 et al.<\/em> 2023<\/a>) was published in the journal Nature<\/em><\/a> last week that, perhaps surprisingly, garnered comparatively little attention. It describes an enormous landslide that occurred from the Annapurna mountain range in Nepal, effecively decaptitating one of the largest peaks.\u00a0 The authors estimate that the landslide had a volume of about 23 cubic kilometres.<\/p>\n

That a very large mass movement occurred in the Annapurna area is not new.\u00a0 The city of Pokhara, the second largest in Nepal, is built on a series of enormous terraces that had previously been identified as being the aftermath of one or more catastrophic debris flows (see for example Fort 2010<\/a>).\u00a0 These had been dated to about 500 years BP, but the origin of this landslide sequence was less clear.<\/p>\n

Lav\u00e9 et al.<\/em> (2023)<\/a> have examined the geology the area, concluding that the source was an enormous rock avalanche, which they are terming the Sabche rockslide, originating from the Annapurna Massif. They have dated this to about the year 1200.\u00a0 The Google Earth image below shows the source zone:-<\/p>\n

\"Google

Google Earth image of the source zone of the Sabche rockslide from the Annapurna massif in Nepal.<\/em><\/p><\/div>\n

.<\/p>\n

The sediments in the central part of this bowl are predominantly limestone brecchias, which are considered by the authors to be the remnants of the rock avalanche.\u00a0 Note also the much more recent deposit from the huge, but very much smaller, Seti Valley rock avalanche in May 2012<\/a>, which a group of us pieced together on this blog.<\/p>\n

The authors have attempted to reconstruct the original topography, and thus the approximate scale of the Sabche rockslide, in this diagram from the paper:-<\/p>\n

\"A

A reconstruction of the Sabche rockslide from Nepal, from Lav\u00e9 et al. (2023)<\/a>.<\/em><\/p><\/div>\n

.<\/p>\n

In the diagram to the left, the rear scarp of the landslide is outlined in purple, whilst the thickness of the brecchia is in the blue-red colour-scale.\u00a0 The extent of the runout of the landslide is shown. Lav\u00e9 et al.<\/em> (2023)<\/a> postulate that in the century after the landslide, an enormous amount of sediment remobilisation occurred, moving the brecchia from its initial position downstream to create the enormous terraces in the Pokhara area.\u00a0 It is fascinating that this appears to have occurred very rapidly after the landslide – the mechanisms for this are unclear to me.<\/p>\n

Finally, it is interesting to speculate on the trigger for the landslide.\u00a0 One possibility is an earthquake, but there is no recorded event in the Himalayas for this time.\u00a0 Thus, it is unlikely to have been a large seismic event, but one cannot discount a more localised, shallow crustal earthquake.\u00a0 Another possibility is climatic forcing – the Sabche rockslide occurred in the Medieval Climate Anomaly<\/a>, when temperatures are thought to have been higher in the Himalayas.\u00a0 However, some megalandslides occur through progressive failure<\/a>, requiring no external trigger.\u00a0 This may be the case here.<\/p>\n

Overall, this is a fascinating paper that should spur further research into this landslide, and into the possibility of similar events elsewhere in the Himalayas.\u00a0 The great challenge now will be to undertake further work within the source zone of the Sabche rockslide – this is an area that is extremely difficult to access, so it will be quite an adventure.<\/p>\n

.<\/p>\n

References<\/p>\n

Fort, M. 2010.\u00a0 The Pokhara Valley: A Product of a Natural Catastrophe. In: Migon, P., Geomorphological Landscapes of the World<\/a>. Springer. pp 265-274.<\/p>\n

Lav\u00e9, J., Gu\u00e9rin, C., Valla, P.G.\u00a0et al. <\/i>2023.\u00a0Medieval demise of a Himalayan giant summit induced by mega-landslide<\/a>.\u00a0Nature<\/i>\u00a0619<\/b>, 94\u2013101 (2023). https:\/\/doi.org\/10.1038\/s41586-023-06040-5<\/a><\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

A new paper in the journal Nature (Lav\u00e9 et al. 2023) describes the 23 cubic km Sabche rockslide in Annapurna, Nepal, which occurred about 850 years ago.<\/p>\n","protected":false},"author":22,"featured_media":44187,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[544],"tags":[469,18,30746,66,17,788,72],"class_list":["post-44184","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-review-of-a-paper","tag-featured","tag-himalayas","tag-megalandslide","tag-nepal","tag-research","tag-review-of-a-paper-2","tag-south-asia"],"_links":{"self":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/44184","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/users\/22"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/comments?post=44184"}],"version-history":[{"count":0,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/44184\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media\/44187"}],"wp:attachment":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media?parent=44184"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/categories?post=44184"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/tags?post=44184"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}