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

C Zangerl,C Prager,C Fey

doi:10.1007/s10064-019-01516-z

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.

Highlights

Deep-seated rock slides, located in well-foliated, mica-rich metamorphic rock masses, are usually compound slides characterised by significant internal fracturing and distortion of the displaced mass (Hungr et al 2014)
The complex mechanical interaction of different active slabs arranged on top of and/or laterally to each other have to be considered and often modelled in combination with large discrete shear displacements. This complex geomechanical behaviour has a considerable impact on the overall slope stability, and an understanding of such rock slide processes is crucial for risk and hazard assessment
This study presents the results of a more than 10-year-long field investigation and remote sensing monitoring campaign

Summary

Introduction

Deep-seated rock slides, located in well-foliated, mica-rich metamorphic rock masses, are usually compound slides characterised by significant internal fracturing and distortion of the displaced mass (Hungr et al 2014). In order to assess a rock slide and monitor the slope evolution and deformation behaviour (i.e. spatial extent, 3D geometry, kinematics, location and shape of shear zones, slab formation, rock mass fragmentation and debris accumulation), mapping, rock mass characterisation, groundwater and multitemporal 2D/3D deformation data are essential. These data can be obtained from different in situ methods, such as geomorphological and geological mapping, geophysical surveys, geodetic monitoring, and borehole drilling with geophysical logging, hydraulic packer testing, and inclinometer as well as piezometer measurements. - Visual analyses and interpretation of slope deformation processes of the Austrian and German Alpine Clubs (maps dated 1893, 1946, 1969 and 1997, see Table 1)

Methods

Discussion

Conclusion