28 July 2016
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:
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:
Behind the front the debris flow consists of a very debris rich but much more fluid slurry:
As the discharge starts to decline the debris flow creates a narrower channel, leaving deposits (levees) on both flanks:
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):
WSL will have captured this debris flow in their instrumentation. I would imagine that it will be a fascinating dataset.