Relevant Field Areas

Figure 1: Map of Köfels slide

Among the RUNOUT field areas are four sturzstroms candidates: Vaiont in Northeast Italy, Elm and Flims in Switzerland and Köfels in Southwest Austria

The Vaiont slide took place in a narrow valley with steep slopes and a dam blocking one end of the valley. The slide was therefore halted long before the internal friction became dominant and it is difficult to gauge the internal friction in this slide accurately. The slide may, however, provide some information about the initial local dynamics. Fieldwork has established a mapping between the current and original location of various deposits that may be reproduced in the models. This requires a full 3-dimensional model to be implemented and has not been undertaken in the preliminary experiment series reported here.

Of more interest to the problem is the 8.700 years old Köfels landslide in the Ötz valley. It originated along the Fundus crest to the West, crossed the valley and climbed the opposite slope where it entered the Horlach valley. The slide, known as Taufererberg, blocked the valley to form a lake and lake sediments today cover the lower parts of the front. One side of the front is close to the steeper slopes surrounding the Horlach valley but it is not obvious that this obstruction, like at Vaiont, stopped the slide. Rather, the slide appears to have lost its momentum while climbing the gentle slope leading to the valley.

The morphology of the Köfels site indicates that we are dealing with a mechanism different from that associated with other landslides studied by Runout near Tessina in Italy and Bad Goissen in Saltzkammergut. The high water contents found in those slides is responsible for their relentless nature, but it also provides a medium so dissipative that the slides never would be able to move up the slope to Niederthai. In order to accomplish that feat, water must have played only a secondary role during the event.

Here we will use the Köfels slide as a reference for initial model results. Two aspects are of special importance. One is the presence of boulders on the top of the slide between Hoher Stein and Wolfsegg. These boulders are large with dimensions measuring tens of meters and very sharp edges. They are furthermore forming what appears to be a slightly disturbed jigsaw puzzle. From this we conclude that the boulders were only slightly disturbed during the transport across the Ötz valley. Although larger slabs were broken into fragments, the buffeting between fragments must have been minimal. The shape and position of the boulders also eliminate the possibility that they were rolling during the transfer. This impression is further enhanced at the head of the slide where we find overlapping boulders reminiscent of falling dominoes. Here, the direction of the slabs indicates that the head of the slide decelerated and was overtaken. The other aspect worth noticing is the shape of the Taufererberg, deep towards the head of the slide and tapering off towards the tail. This again seems to indicate that the slide ran out of steam before reaching the steeper mountain slopes. Unfortunately, the Ötz now flows very close to the slopes below the Fundus crest and it is difficult to determine the original shape of the slide near the origin with any accuracy.

The dynamic properties of the Elm and Flims slides have not yet been included in the model considerations.

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