{"id":15478,"date":"2015-07-13T07:24:32","date_gmt":"2015-07-13T07:24:32","guid":{"rendered":"http:\/\/blogs.agu.org\/landslideblog\/?p=15478"},"modified":"2015-07-13T07:24:32","modified_gmt":"2015-07-13T07:24:32","slug":"umyeonsan","status":"publish","type":"post","link":"https:\/\/blogs.agu.org\/landslideblog\/2015\/07\/13\/umyeonsan\/","title":{"rendered":"The 2011 Umyeonsan debris flows in South Korea"},"content":{"rendered":"<h5>The 2011 Umyeonsan debris flows in South Korea<\/h5>\n<p>On 27th July 2011 an intense rainfall event in Umyeonsan, in Seoul,the capital of South Korea, <a href=\"https:\/\/blogs.agu.org\/landslideblog\/2011\/07\/27\/devastating-landslides-in-south-korea-and-fears-of-more-to-come\/\">killed 16 people and caused widespread damage<\/a>.\u00a0 <a href=\"http:\/\/link.springer.com\/article\/10.1007\/s10346-015-0595-0#\">In a paper just published in the Journal Landslides<\/a>, <a href=\"http:\/\/dx.doi.org\/10.1007\/s10346-015-0595-0\">Jeong <em>et al<\/em> (2015)<\/a> have analysed these landslides in detail.\u00a0 They report that the rainstorm, which had a peak intensity of 112.5 mm, triggered 33 debris flows and 151 landslides.\u00a0 The debris flows caused most of the damage, some of which were caught on dramatic videos:<\/p>\n<p><iframe loading=\"lazy\" src=\"https:\/\/www.youtube.com\/embed\/UeOgKjGUerw\" width=\"480\" height=\"360\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p>.<\/p>\n<p>And<\/p>\n<p><iframe loading=\"lazy\" src=\"https:\/\/www.youtube.com\/embed\/KdeFqRBg_nI\" width=\"640\" height=\"360\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p>.<\/p>\n<p>The study by Jeong <em>et al<\/em> (2015) is impressively detailed.\u00a0 I will highlight two aspects here.\u00a0 First, the density of landslides in the Umyeonsan area is remarkably high.\u00a0 This image from the paper shows the debris flow gullies (in blue) and the landslide initiation points (yellow circles):<\/p>\n<div id=\"attachment_15479\" style=\"width: 577px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/blogs.agu.org\/landslideblog\/files\/2015\/07\/15_07-Unyeonsan-1.gif\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-15479\" class=\"size-full wp-image-15479\" src=\"https:\/\/blogs.agu.org\/landslideblog\/files\/2015\/07\/15_07-Unyeonsan-1.gif\" alt=\"Umyeonsan\" width=\"567\" height=\"455\" \/><\/a><p id=\"caption-attachment-15479\" class=\"wp-caption-text\">Satellite image showing the 33 debris flow gullies (marked in blue) and 151 landslides (i.e., debris flow initiation points denoted by yellow circles) in the 20 watersheds (outlined by white lines) from Jeong et al. (2015)<\/p><\/div>\n<p>.<\/p>\n<p>Jeong <em>et al.<\/em> (2015) ascribe this high density of landslides to a combination of thick colluvium associated with a fault zone, the intense and prolonged rainfall, the steep slopes and the vegetation, which is characterised by low root depths (thus providing little additional strength).<\/p>\n<p>The debris flows themselves are in many ways classic for this type of environment, and are in many ways similar to those observed in natural terrain in Hong Kong.\u00a0 The debris flows started as small failures in colluvium on the hillside, in many cases with multiple small slips occurring in the same catchment.\u00a0 These small failures underwent a rapid mobilisation process and entered the main channel.\u00a0 Jeong et al. (2015) suggest that thereafter the flows eroded and incorporated sediment within the channel, rapidly increasing in size.\u00a0 It is likely that the flows created and broke a series of small dams, possibly partially caused by channel blockage by trees and other woody debris, allowing the creation of large volume, rapid failures.\u00a0 Based on the videos, the authors estimate that one of the failures was traveling at about 28.6 m\/sec when it struck the road.\u00a0 This debris flow killed three people; the effects of such a catastrophic debris flow are truly catastrophic:-<\/p>\n<div id=\"attachment_15482\" style=\"width: 650px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/blogs.agu.org\/landslideblog\/files\/2015\/07\/15_07-Unyeonsan-2-e1436771328290.jpg\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-15482\" class=\"size-full wp-image-15482\" src=\"https:\/\/blogs.agu.org\/landslideblog\/files\/2015\/07\/15_07-Unyeonsan-2-e1436771328290.jpg\" alt=\"Umyeonsan\" width=\"640\" height=\"402\" \/><\/a><p id=\"caption-attachment-15482\" class=\"wp-caption-text\"><a href=\"https:\/\/www.flickr.com\/photos\/pingsooinseoul\/6044152264\/in\/photostream\/\">Via Flickr<\/a><\/p><\/div>\n<p>.<\/p>\n<h5>Reference<\/h5>\n<p>Jeong, S., Kim, Y., Lee, J. and Kim, J. 2015. The 27 July 2011 debris flows at Umyeonsan, Seoul, Korea.\u00a0<em> Landslides.<\/em> <a href=\"http:\/\/dx.doi.org\/10.1007\/s10346-015-0595-0\">http:\/\/dx.doi.org\/10.1007\/s10346-015-0595-0<\/a><\/p>\n<!-- AddThis Advanced Settings generic via filter on the_content --><!-- AddThis Share Buttons generic via filter on the_content -->","protected":false},"excerpt":{"rendered":"<p>In July 2011 33 debris flows occurred in Umyeonsan in South Korea, killing 16 people. In a new paper, Jeong et al. have analysed these landslides in detail, finding that they were initiated as small surperficial landslides that became highly mobile in the river channels, eroding and incorporating large amounts of sediment to create the catastrophic flows.<!-- AddThis Advanced Settings generic via filter on wp_trim_excerpt --><!-- AddThis Share Buttons generic via filter on wp_trim_excerpt --><\/p>\n","protected":false},"author":22,"featured_media":15482,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[544],"tags":[57,881,469,959,788,52],"class_list":["post-15478","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-review-of-a-paper","tag-debris-flow","tag-east-asia","tag-featured","tag-landslide-report","tag-review-of-a-paper-2","tag-south-korea"],"_links":{"self":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/15478","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=15478"}],"version-history":[{"count":0,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/15478\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media\/15482"}],"wp:attachment":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media?parent=15478"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/categories?post=15478"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/tags?post=15478"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}