Moraine collapse 22. May 2009, photo page
Recession of Unterer Grindelwaldgletscher caused steep lateral moraines up to 240 meters high. In 2005 repeated moraine collapses lead to the loss of an alpine hut at Stieregg. A new hut was later contructed higher up. Its warden, Hansruedi Burgener and his son witnessed, and were able to record particularly large collapse events on 22. May 2009.
Beginning of the most spectacular event during which an estimated 300'000 cubic meters of moraine material got displaced. B1 and B2 are particular blocks referred to in the following images.
Since the detached mass accelerates, due to friction at its base, much less than theoretically possible on an inclined plane, the large block B2 begins to roll downwards. B1 one is perched on top of B2.
B2 has rotated almost 180 degrees, and B1 is now in front of it, detaching itself. The first debris has reached the glacial lake on the lower right.
The impact of the colossal block B2 into the lake causes a spectacular splash. Most of the moving mass of moraine is still following, higher up on the left, and much more slowly.
The water jets caused by the impact of block B2 are now fully developed.
The initial jets begin to collapse. Note impacts of smaller debris on the lake at far right.
Waves generated by the impact of block B1 move radially outwards and are about to reach the lake's opposite shore.
Wave action removes some debris cover of the glacier ice forming the lake's shore.
|Photos Hansruedi Burgener and son, Lütschental|