28 July 2016

Illgraben debris flow video

Posted by dr-dave

Illgraben debris flow video

The Illgraben is a very active alpine catchment located near to the near the village of Susten (Leuk), in Canton Valais, Switzerland.  This catchment is particularly interesting because it generates a large number of debris flows, some of which are very large.  Since 2000 WSL has been using Illgraben as a monitoring site for debris flows.  They have installed instrumentation in the catchment and in the debris flow channel.  Not surprisingly, cameras are a part of the set-up, meaning that several large debris flows have been recorded.  WSL has also built a warning system for the catchment in order to protect the local population.

Pierre Zufferey has recently posted a video of one such debris flow on Youtube.  This event occurred on 22nd July 2016 according to the Youtube page.  It is truly spectacular:

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In one film this video illustrates many of the characteristic elements of a debris flow.  So, for example, the front of the flow consists of large number of (in this case) huge boulders tumbling chaotically:

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The boulder-dominated front of the Illgraben debris flow, via Youtube

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Behind the front the debris flow consists of a very debris rich but much more fluid slurry:

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The main, more fluid portion of the Illgraben debris flow, via Youtube

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As the discharge starts to decline the debris flow creates a narrower channel, leaving deposits (levees) on both flanks:

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Declining flow in the Illgraben debris flow, via Youtube

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By the end of the video the flow has migrated into the centre of the channel, leaving new debris flow deposits on either bank, and creating a morphology very similar to that before the flow arrived (see the first picture above):

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The final phase of the Illgraben debris flow, via Youtube

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WSL will have captured this debris flow in their instrumentation.  I would imagine that it will be a fascinating dataset.