Reconstructing the evolution of a deep seated rockslide (Marzell) and its response to glacial retreat based on historic and remote sensing data

In this study a combination of different topographic data from historic topographic maps and remote sensing is used to reconstruct and monitor the behaviour of the high alpine ice contact rockslide system Marzell and its response to glacial debuttressing in the Eastern Alps. Topographic data from archives (historical topographic maps, national glacier inventories, aerial images, orthoimages and ALS data) and data from monitoring campaigns (geodetic measurements, terrestrial laser scanning and UAV imaging campaigns) are processed to georeferenced images and/or elevation data, respectively. The data from different data sources is compiled and analysed with the aim to i) reconstruct the extent, thickness and volume changes of the glacier since 1893 and ii) to analyse the rockslide deformation evolution by extracting information about the displacement direction, dip angle, velocity and partial failure of rockslide slabs since 1951. The rockslide is compound of different rockslide slabs which move downwards as rigid blocks along basal shear zones. The analyses and interpretation of the data suggest a rotational type of rockslide failure mechanisms. The rockslide activity correlates with the ice volume loss at the adjacent part of the glacier. In the period between 1971 and 1997 the annual average rockslide activity was about 0.05 m/a and the annual average ice thickness loss was 0.1 m/a. Since the end of the last century the annual average ice thickness loss increased dramatically to 5 m/a. In that period the rockslide activity accelerated. The highest rockslide activity (up to 1.5 m/a) was observed in the 2000s when half of the slope toe was exposed because of glacier retreat. Since 2010 a deceleration of the rockslide can be observed. In the vicinity of the rockslide the glacier almost disappeared and lost 99.88% of its ice volume between 1893 and 2014. The geomorphological and geological information gathered about the rockslide evolution and the glacier retreat form the base for further rockslide analyses and allow to study and model the influence from glacial debuttressing. (C) 2017 Elsevier B.V. All rights reserved.