{"id":6820,"date":"2013-08-31T06:53:04","date_gmt":"2013-08-31T06:53:04","guid":{"rendered":"http:\/\/blogs.agu.org\/landslideblog\/?p=6820"},"modified":"2013-08-31T06:53:04","modified_gmt":"2013-08-31T06:53:04","slug":"rock-avalanche-in-alaska","status":"publish","type":"post","link":"https:\/\/blogs.agu.org\/landslideblog\/2013\/08\/31\/rock-avalanche-in-alaska\/","title":{"rendered":"Another large rock avalanche in Alaska"},"content":{"rendered":"

The NASA Earth Observation website has another example<\/a> of a recent large rock avalanche in Alaska.\u00a0 Once again this event was detected by Colin Stark, Goran Ekstrom<\/a> and Cl\u00e9ment Hilbert of Columbia University using the\u00a0 global seismic network.\u00a0 This approach gives pretty good data on the size, duration and run-out distance of the landslide; the location of the event was then pinned down by NASA staff using Landsat 8 satellite imagery.\u00a0 The location is in\u00a0in Wrangell-St. Elias National Park just east of Mount Jarvis.<\/p>\n

The NASA site provides images of the landslide a few hours before failure and a few days after.\u00a0 This is the pre-failure image, which was collected by the French Pleiades satellite sensor:<\/p>\n

\"13_08<\/a><\/p>\n

..<\/p>\n

Note the tension cracks, which have been highlighted on the image, showing active deformation.\u00a0 The location of the landslide just above the snout of the glacier is interesting – I wonder if this is a coincidence.<\/p>\n

The post-event image shows the landslide very clearly:<\/p>\n

\"13_08<\/a><\/p>\n

..<\/p>\n

The landslide has clearly detached as defined by the pre-failure tension cracks and then descended straight almost across the valley.\u00a0 There is some evidence of super-elevation on the opposite valley wall, and the landslide seems to have preferentially deposited larger boulders in this area.\u00a0 The flow has then turned 90 degrees to flow down the valley.\u00a0 The shape of the glacier snout is still visible beneath the debris, suggesting that the landslide ran over the ice rather then entraining it.\u00a0 The runout distance is not particularly great for a landslide of this size (the estimated volume is about 20 million tonnes).\u00a0 The valley is now blocked by the debris, suggesting that a lake will develop (there is already a small pond).<\/p>\n

The landslide source area appears to have an interesting morphology, with a large bowl-shaped scarp in the upper slope, and a more linear shape lower down.\u00a0\u00a0\u00a0 This is not unusual for rock avalanches.\u00a0 On eastern side of the scarp there appears to be another tension crack, which may the start of the next failure.\u00a0 The NASA article considers the likely trigger of the landslide, with Colin Stark suggesting melting permafrost as being a potential factor.\u00a0 This is indeed the case, but it is worth noting that the progressive failure mechanism, which is commonly important in non-seismic rock avalanches, does mean that no triggering mechanism is required.<\/p>\n","protected":false},"excerpt":{"rendered":"

Colin Stark and Goran Ekstrom have detected another spectacular rock avalanche in Alaska. It occurred on 25th July near to Mount Jarvis.<\/p>\n","protected":false},"author":22,"featured_media":6823,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[340,469,959,306,521,48],"class_list":["post-6820","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-landslide-report","tag-alaska","tag-featured","tag-landslide-report","tag-rock-avalanche","tag-satellite-image","tag-usa"],"_links":{"self":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/6820","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=6820"}],"version-history":[{"count":0,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/6820\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media\/6823"}],"wp:attachment":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media?parent=6820"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/categories?post=6820"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/tags?post=6820"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}