Unprecedented speed-up and bare ice evidence at the rock glacier Hochebenkar (Ötztal Alps, Austria).

Abstract ID: 3.9222 | Not reviewed | Requested as: Poster | TBA | TBA

Martin Stocker-Waldhuber (1)
Lea, Hartl (1,2); Bernd, Seiser (1); Giulia, Bertolotti (1); Andreas, Gschwentner (1); Andrea, Fischer (1)

(1) Institute for Interdisciplinary Mountain Research, Austrian Academy of Sciences, Innrain 25, 3.OG, 6020, Innsbruck, AT
(2) Alaska Climate Research Center, University of Alaska Fairbanks, 2156 Koyukuk Drive, Fairbanks, AK 99775, USA

Categories: Cryo- & Hydrosphere
Keywords: rock glacier, destabilisation, mass movement, permafrost

Categories: Cryo- & Hydrosphere
Keywords: rock glacier, destabilisation, mass movement, permafrost

Abstract

The rock glacier in the outer Hochebenkar (46°50’0″N, 11° 0’30″E, Ötztal Alps, Austria) has been subject to velocity measurements since as early as 1938 when first investigations using terrestrial photogrammetry aimed to quantify the movement of the rock glacier. From 1951 to 2007, geodetic methods came into operation and were eventually replaced by dGNSS observations. Aside from the discontinued early measurements and minor data gaps, velocity data is available at annual resolution since 1997 from 4 cross sections and a longitudinal profile. Each profile consists of 6 to 12 individual block positions.
Results from the early measurements showed annual rates of rock glacier motion in the order of a few metres. Highest rates up to 4 m/a were measured during the late 1950s and early 1960s and analysis of historic aerial imagery similarly indicates accelerated, destabilised movement of the lower section of the rock glacier during this time. However, for the majority of the time series since then, the flow velocity was hardly more than 1 m/a on average at all stone positions. A short acceleration phase was observed in 2004, maybe as a consequence of the summer 2003, followed by a deceleration and annual movement rates of 1-2 m/a. Since 2018 an exponential increase of rock glacier motion has been observed in the lowest section, showing the destabilisation of this part of the rock glacier. During the last 3 years, maximum displacement values at individual blocks increased from 20 m/a to almost 50 m/a (2024).
Aside from the in-situ measurements, the destabilisation is also evident from the appearance of the rock glacier surface with the increasing formation of crevasse like surface structures and unstable rocks. Bare ice became visible for the very first time in summer 2021 in a small crevasse, and in summer 2024 at the front face of a small step. In winter 2025, a deep crevasse opened within a few weeks across the entire rock glacier width. At depths of around 3 metres an almost continuous conglomerate of stones and ice was exposed at the steep crevasse walls, which enabled ice sampling in February 2025.

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