Deformation characteristics and multi-slab formation of a deep-seated rock slide in a high alpine environment (Bliggspitze, Austria)

Abstract

This study presents the results of a more than 10-year-long field investigation and remote sensing monitoring campaign of a highly active deep-seated rock slide located in a glacial to periglacial environment (Bliggspitze, Tyrol, Austria). Data concerning (i) the terrain surface displacements based on imagery (webcam time-lapse, ortho-images) and both terrestrial and airborne laser scanning, and (ii) the geological-structural and geomorphological situation were analysed to develop a geological-geometrical model of the rock slide and to study the temporally variable activity behaviour and the formation of individual rock slide slabs. Results clearly show that at least seven rock slide slabs were formed at different times and under different slope stability conditions. Some of these rock slide slabs were displaced at slow to moderate velocities and reached scarp offsets of several tens of metres, whereas other, shallower slabs collapsed and formed extremely rapid rock falls and avalanches. Generally, the rock slide is affected by rock mass cataclasis, fracturing and loosening, which in turn cause extensive mass loss accompanied by debris accumulation at lower parts of the slope. The cause for the development of the Bliggspitze rock slide is poorly understood. However, there are clear indications that permafrost degradation and/or glacial retreat, particularly at the foot of the slide, during the recent decades may have adversely affected the slope stability situation.