Rock Avalanche

Hermanns, Reginald L.; Penna, Ivanna; Oppikofer, Thierry; Noël, François; Velardi, Greta

doi:10.1016/b978-0-12-818234-5.00183-8

Cited by 4 publications

(1 citation statement)

References 113 publications

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“…Further classifying this landslide is, however, not straightforward for two reasons: (1) The material involved was mainly debris (talus, colluvium) which would make the landslide a debris avalanche (sensu Hungr et al 2014). However, it is important to stress that the debris was cemented by permafrost and behaved mechanically as a rock avalanche: a granular flow of boulder material (blocky material, very to extremely rapid movement (Hungr et al 2014;Hermanns et al 2021a) (see below), before impacting the lower slope. (2) After the frozen debris avalanche impacted the lower slope, it entrained the material inside the secondary scarp and transitioned into a relatively slower dry debris avalanche and widened downward in the colluvial deposits (sensu Hungr et al 2014).…”

Section: Discussionmentioning

confidence: 99%

A large frozen debris avalanche entraining warming permafrost ground—the June 2021 Assapaat landslide, West Greenland

et al. 2022

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A large landslide (frozen debris avalanche) occurred at Assapaat on the south coast of the Nuussuaq Peninsula in Central West Greenland on June 13, 2021, at 04:04 local time. We present a compilation of available data from field observations, photos, remote sensing, and seismic monitoring to describe the event. Analysis of these data in combination with an analysis of pre- and post-failure digital elevation models results in the first description of this type of landslide. The frozen debris avalanche initiated as a 6.9 * 106 m3 failure of permafrozen talus slope and underlying colluvium and till at 600–880 m elevation. It entrained a large volume of permafrozen colluvium along its 2.4 km path in two subsequent entrainment phases accumulating a total volume between 18.3 * 106 and 25.9 * 106 m3. About 3.9 * 106 m3 is estimated to have entered the Vaigat strait; however, no tsunami was reported, or is evident in the field. This is probably because the second stage of entrainment along with a flattening of slope angle reduced the mobility of the frozen debris avalanche. We hypothesise that the initial talus slope failure is dynamically conditioned by warming of the ice matrix that binds the permafrozen talus slope. When the slope ice temperature rises to a critical level, its shear resistance is reduced, resulting in an unstable talus slope prone to failure. Likewise, we attribute the large-scale entrainment to increasing slope temperature and take the frozen debris avalanche as a strong sign that the permafrost in this region is increasingly at a critical state. Global warming is enhanced in the Arctic and frequent landslide events in the past decade in Western Greenland let us hypothesise that continued warming will lead to an increase in the frequency and magnitude of these types of landslides. Essential data for critical arctic slopes such as precipitation, snowmelt, and ground and surface temperature are still missing to further test this hypothesis. It is thus strongly required that research funds are made available to better predict the change of landslide threat in the Arctic.

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Section: Discussionmentioning

confidence: 99%

A large frozen debris avalanche entraining warming permafrost ground—the June 2021 Assapaat landslide, West Greenland

et al. 2022

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Rock avalanches in northeastern Baffin Island, Canada: understanding low occurrence amid high hazard potential

Matthew,

Gosse,

Hermanns

et al. 2024

Landslides

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Rock avalanches in fjord environments can cause direct catastrophic damage and trigger secondary submarine landslides and tsunamis. These are well-documented in Greenland, Norway, and Alaska but have gone largely unreported in the extensive fjord terrain of the eastern Canadian Arctic. We provide the first inventory of rock avalanche deposits in northeastern Baffin Island—a region characterized by moderate to high seismic hazard, steep and high-walled fjords and glacial valleys, active deglaciation, and observed climate warming. Over a broad study area of ~60,000 km2, one sixth of the terrain had sufficient slope height and gradient to potentially generate rock avalanches. Within that hazard zone, we identified eight rock avalanche deposits at six locations. Only three rock avalanche deposits at two locations are dated, using aerial imagery (1958-present), to the last century while five deposits at four locations are inferred as syn- to post-glacial, likely occurring shortly after local debuttressing. These total numbers fall well below documented inventories from Greenland, Norway, and Alaska. We hypothesize that (1) continuous permafrost persists throughout this region and continues to act as a stabilizing factor and (2) rock mass quality is high in areas of most extreme relief contrast within the study region relative to analogous high-latitude fjord systems such as those in southwestern Greenland. We suggest that Baffin Island is currently in a period of quasi-stability that follows the intense instability during initial deglaciation, yet precedes the higher anticipated slope instability that may occur during permafrost degradation.

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Two similar permafrost degradation landslides at Paatuut, West Greenland, caused tsunamis of substantially different magnitudes

Svennevig,

Keiding,

Sørensen

et al. 2024

Landslides

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On November 21, 2000 CE, the c. 48 × 106 m3 Paatuut landslide in West Greenland triggered a tsunami with a maximum runup height of c. 45 m. Although a field team examined the landslide in the immediate aftermath, prior events and processes, in addition to the cause of the landslide, were never studied. We combined field data, satellite images, and historical photos to bridge this knowledge gap. Our investigation unveiled that a hitherto unknown c. 55 × 106 m3 landslide occurred at the same slope in May or June of 1996. This landslide was a frozen debris avalanche, and we suggest a result of permafrost degradation since c. 1949. The subsequent 2000 landslide and tsunami removed and obscured the traces of the 1996 landslide. Interestingly, the 1996 landslide caused a tsunami with a runup height of only 15 m near the landslide impact area, one-third of the 2000 tsunami. We applied tsunami modelling and interpretation of morphological field evidence to explore why these volumetrically similar landslides on the same slope could produce markedly different tsunami runup heights. The deposit of the 1996 landslide on the coastal slope produced a large, unconsolidated, wet sediment volume that could be entrained in the 2000 landslide, and in addition, reducing the basal friction of this later event. Furthermore, differences in drop height and rheology between the two landslides may explain the different tsunamigenic potential. We see evidence of much older post-glacial landslide activity on the slope, constituting a static preconditioning factor for the landslides. The 1996 and 2000 landslides demonstrate the incomplete record of large landslides in the Arctic and the importance of considering the runout path, substrate, and entrainment in determining the tsunamigenic potential of landslides. Above all, they also demonstrate the sensitivity of these Arctic slopes to global warming and associated permafrost degradation.

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Rock Avalanche

Cited by 4 publications

References 113 publications

A large frozen debris avalanche entraining warming permafrost ground—the June 2021 Assapaat landslide, West Greenland

A large frozen debris avalanche entraining warming permafrost ground—the June 2021 Assapaat landslide, West Greenland

Rock avalanches in northeastern Baffin Island, Canada: understanding low occurrence amid high hazard potential

Two similar permafrost degradation landslides at Paatuut, West Greenland, caused tsunamis of substantially different magnitudes

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