{"id":6026,"date":"2013-02-24T12:11:24","date_gmt":"2013-02-24T12:11:24","guid":{"rendered":"http:\/\/blogs.agu.org\/landslideblog\/?p=6026"},"modified":"2013-02-25T14:56:41","modified_gmt":"2013-02-25T14:56:41","slug":"an-intrepretation-of-the-mount-dixon-rock-avalanche-in-new-zealand-using-satellite-imagery","status":"publish","type":"post","link":"https:\/\/blogs.agu.org\/landslideblog\/2013\/02\/24\/an-intrepretation-of-the-mount-dixon-rock-avalanche-in-new-zealand-using-satellite-imagery\/","title":{"rendered":"An intrepretation of the Mount Dixon rock avalanche in New Zealand using satellite imagery"},"content":{"rendered":"<p>Last month I posted on a couple of occasions about the <a href=\"https:\/\/blogs.agu.org\/landslideblog\/2013\/01\/21\/first-reports-of-a-large-landslide-on-mount-cook-in-new-zealand\/\">Mount Dixon rock avalanche in New Zealand<\/a>, which was caught on a <a href=\"https:\/\/blogs.agu.org\/landslideblog\/2013\/01\/28\/the-video-of-the-mount-dixon-aoraki-mount-cook-rock-avalanche-in-motion\/\">memorable video by Neil Wiltshire<\/a>.\u00a0 In the aftermath of the landslide, <a href=\"http:\/\/earthobservatory.nasa.gov\/IOTD\/view.php?id=80427\">NASA collected a satellite image of it using their EO-1 ALI instrument<\/a>.\u00a0 This image, and a comparator image of the site before the landslide,<a href=\"http:\/\/earthobservatory.nasa.gov\/IOTD\/view.php?id=80427\"> are now available online<\/a>.<\/p>\n<div id=\"attachment_6027\" style=\"width: 650px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/blogs.agu.org\/landslideblog\/2013\/02\/24\/an-intrepretation-of-the-mount-dixon-rock-avalanche-in-new-zealand-using-satellite-imagery\/13_02-mount-dixon-before\/\" rel=\"attachment wp-att-6027\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-6027\" class=\"size-full wp-image-6027\" title=\"13_02 Mount Dixon before\" src=\"https:\/\/blogs.agu.org\/landslideblog\/files\/2013\/02\/13_02-Mount-Dixon-before-e1361704977570.jpg\" alt=\"\" width=\"640\" height=\"426\" \/><\/a><p id=\"caption-attachment-6027\" class=\"wp-caption-text\">A NASA EO-1 ALI image of Mount Dixon before the landslide<\/p><\/div>\n<div id=\"attachment_6028\" style=\"width: 650px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/blogs.agu.org\/landslideblog\/2013\/02\/24\/an-intrepretation-of-the-mount-dixon-rock-avalanche-in-new-zealand-using-satellite-imagery\/13_02-mount-dixon-after\/\" rel=\"attachment wp-att-6028\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-6028\" class=\"size-full wp-image-6028\" title=\"13_02 Mount Dixon after\" src=\"https:\/\/blogs.agu.org\/landslideblog\/files\/2013\/02\/13_02-Mount-Dixon-after-e1361705117659.jpg\" alt=\"\" width=\"640\" height=\"426\" \/><\/a><p id=\"caption-attachment-6028\" class=\"wp-caption-text\">A NASA EO-1 ALI image of the Mount Dixon rock avalanche<\/p><\/div>\n<p>As a reminder, this is the video that Neil Wiltshire collected of the landslide:<\/p>\n<p><iframe loading=\"lazy\" title=\"Mt Dixon Rock Fall 21\/01\/2013\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/E28_3uj9K0g?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe><\/p>\n<p>.<\/p>\n<p>The comparison between the video and the image is very revealing.\u00a0 <a href=\"https:\/\/blogs.agu.org\/landslideblog\/2013\/02\/12\/the-full-video-of-the-mount-dixon-rock-avalanche-from-aoraki-mount-cook-national-park-in-new-zealand\/\">As I pointed out in my earlier post<\/a>, the video shows that the landslide with through a rapid transition from a rock avalanche phase (basically a chaotic jumble of rock and ice moving at high-speed) into a sliding phase.\u00a0 If you look carefully at the above image you can see this transition line really clearly.\u00a0 I have annotated the image below to try to highlight the different phases of movement:<\/p>\n<p><a href=\"https:\/\/blogs.agu.org\/landslideblog\/2013\/02\/24\/an-intrepretation-of-the-mount-dixon-rock-avalanche-in-new-zealand-using-satellite-imagery\/13_02-mount-dixon-1\/\" rel=\"attachment wp-att-6029\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-6029\" title=\"13_02 Mount Dixon 1\" src=\"https:\/\/blogs.agu.org\/landslideblog\/files\/2013\/02\/13_02-Mount-Dixon-1-e1361706152290.jpg\" alt=\"\" width=\"640\" height=\"889\" \/><\/a>.<\/p>\n<p>So my interpretation is as follows:<\/p>\n<p>1. The landslide detached from the near vertical flank of Mount Dixon and fell about 500 metres;<\/p>\n<p>2. In the impact zone it fragmented and transitioned into a rock avalanche<\/p>\n<p>3. In the upper track the rock avalanche has left almost no debris and indeed appears to have eroded away a part of the glacier (in the centre of the track), which will have increased the volume of mobile mass through entrainment<\/p>\n<p>4. In the lower track the rock avalanche starts to leave some small amount of material behind, suggesting the entrainment and deposition are starting to balance.\u00a0 Note that it appears that there are two different erosion tracks in this phase, with the split occurring just above the point that I have marked as lower track.<\/p>\n<p>5. At the transition line the rock avalanche appears to suddenly change into sliding mode, and large-scale deposition starts<\/p>\n<p>6. As the video shows the main landslide motion ends with a transition to a creep phase.<\/p>\n<p>A really interesting question is what this transition point represents?\u00a0 Is this a point at which the slope gradient changes, which means that the landslide rapidly slowed? Or was the landslide losing velocity along track (imagine that velocity was initially high at the foot of the cliff, but the slope gradient was too low to allow that velocity to be maintained).\u00a0 Thus, did the landslide reach a point at which the velocity was too low to maintain an avalanche state?\u00a0 Or thirdly, intriguingly, was this change initiated by a change in the underlying glacier?\u00a0 Take a look at the &#8220;before&#8221; satellite image &#8211; you&#8217;ll see that the lower track is characterised by crevasses.\u00a0 At about the transition point this changes to smooth ice.\u00a0 So, did this change in the basal conditions lead to a change in the landslide?<\/p>\n<p>Many people will now be working on this landslide, so I will leave it to them to sort it out.\u00a0 I will try to post again about the landslide when the research is published.\u00a0 There is no doubt that this will provide a significant insight into the somewhat enigmatic behaviour of these large landslides.<\/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>This post provides an interpretation of the Mount Dixon rock avalanche using NASA EO-1 ALI imagery collected shortly after the event.  It shows that the landslide went through a dramatic transition from rock avalanche to sliding<!-- 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":6029,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[598],"tags":[469,963,7,306,521],"class_list":["post-6026","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-landslide-processes","tag-featured","tag-landslide-video","tag-new-zealand","tag-rock-avalanche","tag-satellite-image"],"_links":{"self":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/6026","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=6026"}],"version-history":[{"count":0,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/6026\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media\/6029"}],"wp:attachment":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media?parent=6026"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/categories?post=6026"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/tags?post=6026"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}