High mountain rockfall dynamics: rockfall activity and runout assessment under the aspect of a changing cryosphere

Abstract

Rockfalls are a major aspect concerning morphodynamics in high mountain areas and represent a serious hazard for people and infrastructure. Recently, an increase of rockfall activity has been observed which is probably related to the destabilization of rock slopes through climate-related changes of the mountain cryosphere. This study investigates the rockfall distribution during a 4-year monitoring period by systematic observation with bitemporal Airborne Laser Scanning DTMs in an area of 610.7 km² in the Ötztal Alps/Tyrol, Austria. The analyses of the 93 detected rockfall events indicate that rockfall activity is highest in proglacial areas. Further 83.9% of all rockfall source areas were mapped in bedrock where the modelled mean annual ground temperature (MAGT) indicates perennial frozen conditions. The results demonstrate the importance of thermal effects on the destabilization of rock faces and show that the triggering of rockfalls is closely related to changes in the glacier and permafrost regime. 18 low-magnitude rockfalls with volumes between 69 ± 3 m³ and 8420 ± 89 m³ are examined in detail. On the base of the analysis of these events energy line angles of 28.7°for the Fahrböschung and 19.9°for the minimum shadow angle can be derived and significantly longer runout distances on glaciated rockfall paths are observed.

Triggers of present-day rockfalls in the zone of sporadic permafrost in non-glaciated mountain region: the case study of Turnia Kurczaba (the Tatra Mts., Poland)

“…In many high mountain areas, rockfalls are most frequently caused by the degradation of permafrost as a result of climate warming (Allen & Huggel 2013, Fischer et al 2016, Knoflach et al 2021, with such events typically occurring in summer (Fischer et al 2012, Sass & Oberlechner 2012) -often at times of extremely high air temperatures (Allen & Huggel 2013). In the Tatra Mountains, in addition to the Turnia Kurczaba rockfall studied here, fragments of the rockwalls of Cubryna (23-25 September 2012), Zadný Gerlach (17-19 September 2018), Niebieska Turnia (21 May and 28 September 2018) and Malý Kežmarský štít (18 June 2022) peaks have also fallen in the last decade.…”

“…The high-mountain relief of this area dates back to a series of Pleistocene glaciations (Klimaszewski 1988, Rączkowski et al 2015, Zasadni et al 2022). In the post-glacial period, extensive talus cones with a thickness exceeding 40 m developed at the mouths of gullies (Gądek et al 2016).…”

“…There are many potential rockfall triggers (Mc-Coll 2012). The key ones, sometimes acting simultaneously, include: (a) seismic activity (Kobayashi et al 1990, Deparis et al 2008, Kargel et al 2016), (b) exposure and debuttressing of rockwalls as a result of glacier retreat (Ballantyne 2002, Fischer et al 2006, Oppikofer et al 2008, Ravanel et al 2017, Knoflach et al 2021, and (c) degradation of permafrost (Gruber & Haeberli 2007, Harris et al 2009, Ravanel et al 2010, 2017, Fischer et al 2012, Sala et al 2020, Savi et al 2020, Knoflach et al 2021. Major rockfall triggers also include heavy precipitation events, rapid snow melt, and thermal anomalies (Eberhardt 2006, Allen & Huggel 2013, Luethi et al 2015, Paranunzio et al 2016, 2019, Sala et al 2020.…”

The Taconnaz Rockfall (Mont-Blanc Massif, European Alps) of November 2018: A Complex and At-Risk Rockwall-Glacier-Torrent Morphodynamic Continuum

“…Made up of steep rock faces or superficial formations, covered or not with mobile or immobile ice, the slope is multifaceted and changing. Its evolution with climate change, often conditioned by numerous other factors (e.g., topography, geological structure, lithology), can result in the destabilisation of entire slopes [11,12]. This was the case recently on Piz Cengalo (3369 m a.s.l., Bernina massif, Switzerland).…”

“…This approach allows us to identify triggering conditions, especially the roles of permafrost degradation and glacial retreat-both consequences of the current global warming, which is particularly accelerated in mountainous regions. Furthermore, these events offer insights into runout dynamics [12], notably the effects of supra-glacial pathways on flow patterns [18]. Lastly, comprehending the post-event evolution of scars [19] and documenting changes in deposits and induced impacts on torrential activity are crucial [20].…”