The largest rock avalanches in Patagonia: Timing and relation to Patagonian Ice Sheet retreat

Pánek, Tomáš, Břežný, Michal, Smedley, Rachel ORCID: 0000-0001-7773-5193, Winocur, Diego, Schönfeldt, Elisabeth, Agliardi, Federico and Fenn, Kaja ORCID: 0000-0002-6322-0540
(2023) The largest rock avalanches in Patagonia: Timing and relation to Patagonian Ice Sheet retreat. Quaternary Science Reviews, 302. p. 107962.

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One of the largest concentrations of giant landslides (≥108 m3) in Patagonia is in the eastern part of Lago Cochrane/Pueyrredón (LP) valley in Argentina. In addition to minor earthflows and rock slides, this landslide cluster is dominated by rock and debris avalanches that affect the northern slope of Meseta Belgrano, the largest of which have volumes >1 km3 and a runout of >10 km. To determine the chronology of these large landslides and their relationship to the geological setting and the glacial history related to the Last Glacial Maximum (LGM) ∼20–18 ka ago, we combined geomorphological mapping with absolute dating (luminescence and radiocarbon dating) and numerical modelling of slope stability. Dating and cross-cutting relationships with glaciolacustrine deposits suggest that some of the largest rock avalanches collapsed directly into a glacial lake between ∼17 and ∼12 ka, soon after deglaciation, but some were pre-glacial and landslide activity continued until today, posing a potential hazard to the area. In agreement with these data, numerical modelling suggests that slope stability was only marginally affected by ice retreat and glacial lake drainage, and landslides were most likely favoured by relatively low rock strength, related glacially-conditioned topography, and, possibly, seismic activity. A newly identified active fault at the base of the Meseta Belgrano, whose activity was likely enhanced by postglacial rebound, was probably the key factor that concentrated postglacial rock avalanches into the LP valley. We conclude that exceptionally large (km-scale) landslides can occur on slopes made of relatively weak rocks in a glacially-conditioned topographic setting even without a strong direct triggering effect of deglaciation, while fatigue due to long-term seismicity may promote collapse.

Item Type: Article
Uncontrolled Keywords: Landslides, Rock avalanches, Glacial lake, Deglaciation, Patagonia
Divisions: Faculty of Science and Engineering > School of Environmental Sciences
Depositing User: Symplectic Admin
Date Deposited: 23 Jan 2023 09:04
Last Modified: 20 Jan 2024 02:30
DOI: 10.1016/j.quascirev.2023.107962
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