Presumably after an earthquake the landscape should return to some sort of equilibrium, with the number of landslides active each year reducing with time, on average.\u00a0 But how quickly this occurs is poorly constrained.\u00a0 It might of course vary from place to place according to the climate, geology, vegetation and human activities.\u00a0 This is not a purely academic issue – this effect strongly determines the hazard posed by mountain communities after an earthquake.<\/p>\n
In an open access paper just published in the journal Progress in Disaster Science<\/em> (Rosser et al.<\/em> 2021<\/a>), a multidisciplinary team has examined this question with respect to the 2015 Mw 7.8 Gorkha, Nepal earthquake<\/a>.\u00a0 They have focused on an area heavily affected by landslides in central and western Nepal.\u00a0 There is a great deal of richness in this paper, which also looks at risk management with mountain communities.\u00a0 However, in this post I will focus simply on the question of post-earthquake slope evolution.<\/p>\n The team has mapped landslides in a large study area on multiple occasions since the Gorkha Earthquake.\u00a0 In particular, they have manually mapped landslides twice per year since 2015, before and after the annual monsoon.\u00a0 The area chosen is a large swathe of west and central Nepal.\u00a0 This allows them to compile the following, critically important, diagram showing the trend in landslide occurrence in the landscape with time:-<\/p>\n Changes in mapped landslide numbers and total landslide area between 2014, the Gorkha earthquake in 2015, and post-monsoon 2019, from Rosser et al.<\/em> (2021)<\/a>. Vertical blue bars show the timing of the monsoon; solid black line is landslide number; dashed black line is landslide area; and, the time of the earthquake (orange line) and the first local elections (green lines).<\/p><\/div>\n .<\/p>\n The jump in the number and area of landslides caused by the Gorkha Earthquake in 2015 is clear. As expected, this increases further in the monsoon that year.\u00a0 Interestingly, the number of landslides increased again slightly through the dry season in the winter of 2015-16, which is slightly surprising. After this there was a slow decline in the number of landslides, although this was a quite marginal change, much less than has been seen elsewhere.<\/p>\n Fascinatingly, the area and number of landslides increases markedly again from 2017 onwards, which is definitely unexpected.\u00a0 Rosser et al.<\/em> (2021)<\/a> suggest that this is due to a “proliferation of rural road construction around the time of the first local elections”.\u00a0 The number of landslides in the study area is now in excess of 21,000, more than on the day after the earthquake and after the first monsoon season.<\/p>\n I have highlighted ad nauseam the terrible costs of unconstrained rural road construction in high mountain areas.\u00a0 In the aftermath of the Gorkha Earthquake, Rosser et al.<\/em> (2021)<\/a> have demonstrated well that in central and western Nepal, rural roads are serving to amplify the impacts of the seismic shaking, and to extend them in time.<\/p>\n .<\/p>\n Lin, J-C, Petley, D.N., Jen, C-H.,\u00a0 Hsu, M-L. 2006. Slope movements in a dynamic environment \u2013 A case study of Tachia river, Central Taiwan<\/a>.\u00a0 Quaternary International, <\/em>147<\/strong> (1), 103-112.<\/p>\n Rosser, N., Kincey, M., Oven, K. et al.<\/em> 2021.\u00a0 Changing significance of landslide Hazard and risk after the 2015 Mw 7.8 Gorkha, Nepal earthquake<\/a>, Progress in Disaster Science<\/em><\/a>, 100159,\u00a0 https:\/\/doi.org\/10.1016\/j.pdisas.2021.100159<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":" A new open access paper in the journal Progress in Disaster Science (Rosser et al. 2021) demonstrates that the number of landslides in W. and C. Nepal has increased since the 2015 Gorkha Earthquake.<\/p>\n","protected":false},"author":22,"featured_media":36967,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[544],"tags":[23,469,979,66,192,17,72],"class_list":["post-36964","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-review-of-a-paper","tag-earthquake","tag-featured","tag-monsoon","tag-nepal","tag-paper","tag-research","tag-south-asia"],"_links":{"self":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/36964","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=36964"}],"version-history":[{"count":0,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/36964\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media\/36967"}],"wp:attachment":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media?parent=36964"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/categories?post=36964"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/tags?post=36964"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"Landslide](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2021\/03\/21_03-Nepal-1.jpg\")
References<\/h4>\n