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Understanding Glacier Changes: Risks Posed by Glacial Lakes, Debris Flows

By Guest Writer

Feb 12, 2010

By Kenneth Hewitt, China Dialogue
Part III of a three-part series

Glaciers and their immediate environs present many dangers for humans, such as crevasses and glacier mills into which one might fall, heavily crevassed ice falls, snow and ice avalanches from the side walls and, along the flanks, dumping of great boulders, ponding and floods from melt water. For these reasons, there are hardly ever permanent settlements on or right beside the ice. These are hazards mainly to mountaineers, hunters, travelers and military expeditions.

The more serious dangers arise from processes in the glacial environment that may extend their impacts beyond existing glacial areas. The more serious tend to involve ponding of water that leads to glacial outburst floods, or releases that generate debris flows.

The risk of glacier lake outburst floods has received particular attention in other parts of the Himalaya, notably Bhutan, Nepal and Tibet. In Nepal, some 25 glacial lake outburst floods have been recorded since the 1930s, with especially destructive events in 1985 and 1991. Bhutan also has a number of dangerous lakes, one of which burst with disastrous consequences in 1994. Reports suggest all of these lakes and the triggers for outburst floods are related to climate warming and glacier retreat.

There is also a history of such outburst floods from Karakoram glaciers. However, the problem here is also very different from that recently reported elsewhere in the Himalayas. In particular, the most serious threats involve, specifically, much larger impoundments by short-lived, unstable ice dams. Crucially, all recorded examples have been associated with advancing glaciers.

In fact, the Karakoram presents two rather different groups of outburst floods. The most frequent are relatively local events. Collectively, they threaten dozens if not hundreds of small settlements in the higher valleys and examples occur in most years. They involve a wide variety of dam compositions, forms and outburst types, including ice, moraine, and mixed-barriers.

Conversion of outburst floods into debris flows is quite common, usually the more severe risk. For the upper Indus, these are the only types of damaging outburst floods reported in the past several decades. Moreover, they occur whether glaciers are advancing, retreating and relatively stable. Conversely, the larger Karakoram dams involve impoundment of a main river valley by a relatively large tributary glacier. Most important, in the present context, these dams only form from a vigorous forward push of the ice.

More than 60 glaciers of intermediate-to-large size (10 kilometres to 65 kilometres in length) have a history of advancing into and interfering with tributaries of the upper Indus and Yarkand rivers. Not all are known to have created actual dams, but at least 30 have done so and involved outburst floods of exceptional size and destructiveness. However, while there have been several large dams recently on the Shaksgam, on the Indus the last major ice dam was in 1933. “Major” refers to outburst floods that were large enough to register hundreds of kilometres downstream at the river gauge at Attock, where the river leaves the mountains.

The most urgent questions today involve some Karakoram valleys whose glaciers created ice dams and catastrophic outburst floods in the past and that are advancing right now. Will they impound the rivers again? Three locations require special attention; the Shaksgam, upper Shyok and Shimshal valleys.

The Shaksgam is a tributary of the upper Yarkand. According to satellite imagery, five glaciers that have formed ice dams in the past are advancing at present. One of them, the Kyagar, has created several recent dams.

An outburst from the one in 1999 caused severe damage along the lower Yarkand River in Kashgar district. In the summer of 2009, Kyagar again impounded the river and a 3.5 kilometer-long lake was formed. Fortunately it drained slowly but was close to dimensions that have led to disastrous floods in the past.

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Great blog. There's a lots good data about glacier changes in this blog, though I would like tell you something. I can understand the content, but the navigation doesn't work so good. I never usually post on blogs but I have found this is very useful work.

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I really loved reading your blog. It was very well authored and easy to undertand. Unlike additional blogs I have read which are really not tht good. I also found your posts very interesting. In fact after reading, I had to go show it to my friend and he ejoyed it as well!

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