{"id":20186,"date":"2016-10-25T07:42:33","date_gmt":"2016-10-25T07:42:33","guid":{"rendered":"http:\/\/blogs.agu.org\/landslideblog\/?p=20186"},"modified":"2016-10-25T07:42:33","modified_gmt":"2016-10-25T07:42:33","slug":"aru-mountains-avalanche-1","status":"publish","type":"post","link":"https:\/\/blogs.agu.org\/landslideblog\/2016\/10\/25\/aru-mountains-avalanche-1\/","title":{"rendered":"Structures in the Aru Mountains giant avalanche deposits"},"content":{"rendered":"
Structures in the Aru Mountains avalanche deposits<\/h5>\n

The second enormous Aru Mountains avalanche in Tibet<\/a> that I featured yesterday have been imaged<\/a> by an innovative start-up satellite imagery company called Planet<\/a>, which is launching a constellation of satellites that it is building itself.\u00a0 The quality of the image of the second Aru Mountain avalanche is fantastic, good enough to draw out some very interesting features:-<\/p>\n

\"Aru

The second Aru Mountains avalanche, imaged by Planet<\/a><\/p><\/div>\n

.<\/p>\n

The first key element, that I mentioned yesterday is that it appears to me that this is two separate events, with the deposits lying on top of each other.\u00a0 In the image below I have drawn the boundary between the two.\u00a0 The first event appears to have been larger and to have traveled further:<\/p>\n

\"Aru

Annotated map of the Aru Mountain avalanche deposit, imaged by Planet<\/a><\/p><\/div>\n

.<\/p>\n

The second deposit very clearly lies above the first.\u00a0 The larger, initial, avalanche appears to have had a large lateral offshoot that traveled surprisingly far:<\/p>\n

\"Aru

Annotated image of the second Aru Mountains avalanche, imaged by Planet<\/a><\/p><\/div>\n

.<\/p>\n

At first glance this looks quite illogical as the Planet image from before the avalanche (below) shows that it has crossed a line of elevated ground.\u00a0 However, this offshoot is almost dead in line with original orientation of the glacier.\u00a0 The implication is that the movement was so rapid that it a portion ploughed straight ahead, over the topography.\u00a0 The second avalanche followed the topography, which suggest to me that it\u00a0 was less energetic.\u00a0 The main deposit from the first avalanche has a very nice central flow structure that I have highlighted above as well; this is even visible beneath the second flow.<\/p>\n

\"Aru

The “before” image of the second Aru Mountains avalanche, imaged by Planet<\/a>. The glacier that collapsed can be seen bottom left. The avalanche initially flowed over the topography in line with the glacier. The later part of the first collapse, and the second one, followed the topography into the main valley<\/p><\/div>\n

.<\/p>\n

The dynamics of the flow are very complex, but a key factor is the basal friction.\u00a0 The role that this plays is beautifully illustrated by two elements of the second avalanche that I have highlighted below.<\/p>\n

\"Aru

Annotated image of the second Aru Mountains avalanche, as imaged by Planet<\/a><\/p><\/div>\n

.<\/p>\n

The initial avalanche event flowed over glacial sediment, whilst the second phase flowed mostly over the deposit from the initial event.\u00a0 Thus the basal dynamics, and friction, were very different.\u00a0 I have annotated in black the portion where the second flow was traveling over the Central Flow structure (in blue).\u00a0 This must have been a rougher surface, with more friction, as the second flow has suffered reduced mobility in this area and has traveled less far, as evidenced by a cut out in the boundary of the flow.\u00a0 and in the north of the image the second flow has spilled over onto fresh sediment (annotated in white).\u00a0 The different basal regime is reflected in a very different deposit, with clear flow lines that are not visible elsewhere.<\/p>\n

Thus, the quality of this satellite image allows detailed analysis of this giant avalanche, providing insight into the event.\u00a0 Of course with proper mapping and analysis it would be possible to provide a great deal more understanding.<\/p>\n

Other posts that may be of interest<\/h5>\n