Massive permafrost rock slide under warming polythermal glacier (Bliggspitze, Austria)

• Main Authors: Pfluger, Felix, Weber, Samuel, Steinhauser, Joseph, Zangerl, Christian, Fey, Christine, Fürst, Johannes, Krautblatter, Michael
• Format: Text
• Language: English
• Published: 2024
• Subjects: Ice; permafrost
• Online Access: https://doi.org/10.5194/egusphere-2024-2509; https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2509/

Recent studies have brought upon numerous evidence for enhanced rock slope failure from degrading permafrost rock walls. These failures have been thought to be subaerial and triggered by thermal heat propagation from rising air temperatures into the exposed rock faces. However, we have neglected that, at the same time, the dividing line between cold and warm basal states of polythermal glaciers has shifted some hundreds of meters upwards. This means that previously frozen and ice-filled fragmented rock walls under cold glaciers have suddenly and for the first time in thousands of years been exposed to (i) hydrostatic pressures, (ii) warming and degrading ice in fractures, and (iii) rock mechanical degradation in warming rocks. One of the best case studies is the 3.9 to 4.3 million m 3 rock slide at Bliggspitze on 29 June 2007, which detached from a north-exposed, glacier-covered rock slope at 3200 m above sea level. In this paper, we hypothesize that the transition from cold- to warm-based glaciers, a scarcely observed but widespread phenomenon, caused the massive rock slide. To prove this, we (a) have analyzed the glacier transition since 1971 using aerial photographs coincident to meteo data, (b) compared 2013–2016 Ground Surface Temperature measurements to infer permafrost-prone/cold glacier thermal conditions, (c) categorized springs mapped in summer 2001/2012 according to geomorphological features and mineralization, d) performed Electrical Resistivity Tomography subsequent to failure on the destabilized rock flank in 2009, (e) conducted rock testing in frozen and unfrozen conditions and (f) modeled the mechanical impact of hydrostatic pressure, degradation of permafrost and glacier retreat in a universal distinct element code (UDEC). Aerial photos indicate the existence of a cold glacier from 1971–2003 above the failure volume. On the rock face above the failure volume, ground surface temperature measurements demonstrate permafrost favorable conditions and underpin the presence of ...