Analyses of past and present rock slope instabilities in a fjord valley: Implications for hazard estimations

Böhme, Martina; Oppikofer, Thierry; Longva, Oddvar; Jaboyedoff, Michel; Hermanns, Reginald L.; Derron, Marc‐Henri

doi:10.1016/j.geomorph.2015.06.045

Cited by 44 publications

(28 citation statements)

References 47 publications

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“…Truncation may have a geological reason as it will be discussed in the next section. The truncation or deviation from the trend is also observed in other rockfall records, thus reducing the frequency of large rockfalls several orders of magnitude in relation to the previsions of the power law (Hungr et al 1999;Guzzetti et al 2003;Böhme et al 2015).…”

Section: Mce Based On Discrete Potentially Movable Volumesmentioning

confidence: 67%

Magnitude and frequency relations: are there geological constraints to the rockfall size?

2017

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There exists a transition between rockfalls, large rock mass failures and rock avalanches. The magnitude and frequency relations (M/F) of the slope failure are increasingly used to assess the hazard level. The management of the rockfall risk requires the knowledge of the frequency of the events but also defining the worst case scenario, which is the one associated to the maximum expected (credible) rockfall event. The analysis of the volume distribution of the historical rockfall events in the slopes of the Solà d'Andorra during the last 50 years, shows that they can be fitted to a power law. We argue that the extrapolation of the F-M relations far beyond the historical data is not appropriate in this case. Neither geomorphological evidences of past events nor the size of the potentially unstable rock masses identified in the slope support the occurrence of the large rockfall/rock avalanche volumes predicted by the power law. We have observed that the stability of the slope at the Solà is controlled by the presence of two sets of unfavorably dipping joints (F3, F5) that act as basal sliding planes of the detachable rock masses. The area of the basal sliding planes outcropping at the rockfall scars were measured with a Terrestrial Laser Scanner. The distribution of the areas of the basal planes may be also fitted to a power law that shows a truncation for values bigger than 50 m 2 and a maximum exposed surface of 200 m 2. The analysis of the geological structure of the rock mass at the Solà d'Andorra make us conclude that the size of the failures is controlled by the fracture pattern and that the maximum size of the failure is constrained. Two sets of steeply dipping faults (F1 and F7) interrupt the other joint sets and prevent the formation of continuous failure surfaces (F3 and F5). We conclude that due to the structural control, large slope failures in Andorra are not randomly distributed thus confirming the findings in other mountain ranges.

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Section: Mce Based On Discrete Potentially Movable Volumesmentioning

confidence: 67%

Magnitude and frequency relations: are there geological constraints to the rockfall size?

2017

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“…Several works have been done on rock slope failures in deglaciated mountain settings (e.g. Norway; Böhme et al, 2015;Hilger et al, 2018) where peaks in previous activity have been dated and suggested to reflect glacial debuttressing and climatic change in the form of change in regional precipitation patterns (amount and type) and increase in temperature leading to permafrost degradation. It is, however, unclear whether these conditions translate to the much cooler high-Arctic conditions of West Greenland; more work is needed on this.…”

Section: Preconditioning and Preparatory Factors For Slope Instabilitymentioning

confidence: 99%

Evolution of events before and after the 17 June 2017 rock avalanche at Karrat Fjord, West Greenland – a multidisciplinary approach to detecting and locating unstable rock slopes in a remote Arctic area

et al. 2020

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Abstract. The 17 June 2017 rock avalanche in the Karrat Fjord, West Greenland, caused a tsunami that flooded the nearby village of Nuugaatsiaq and killed four people. The disaster was entirely unexpected since no previous records of large rock slope failures were known in the region, and it highlighted the need for better knowledge of potentially hazardous rock slopes in remote Arctic regions. The aim of the paper is to explore our ability to detect and locate unstable rock slopes in remote Arctic regions with difficult access. We test this by examining the case of the 17 June 2017 Karrat rock avalanche. The workflow we apply is based on a multidisciplinary analysis of freely available data comprising seismological records, Sentinel-1 spaceborne synthetic-aperture radar (SAR) data, and Landsat and Sentinel-2 optical satellite imagery, ground-truthed with limited fieldwork. Using this workflow enables us to reconstruct a timeline of rock slope failures on the coastal slope here collectively termed the Karrat Landslide Complex. Our analyses show that at least three recent rock avalanches occurred in the Karrat Landslide Complex: Karrat 2009, Karrat 2016, and Karrat 2017. The latter is the source of the abovementioned tsunami, whereas the first two are described here in detail for the first time. All three are interpreted as having initiated as dip-slope failures. In addition to the recent rock avalanches, older rock avalanche deposits are observed, demonstrating older (Holocene) periods of activity. Furthermore, three larger unstable rock slopes that may pose a future hazard are described. A number of non-tectonic seismic events confined to the area are interpreted as recording rock slope failures. The structural setting of the Karrat Landslide Complex, namely dip slope, is probably the main conditioning factor for the past and present activity, and, based on the temporal distribution of events in the area, we speculate that the possible trigger for rock slope failures is permafrost degradation caused by climate warming. The results of the present work highlight the benefits of a multidisciplinary approach, based on freely available data, to studying unstable rock slopes in remote Arctic areas under difficult logistical field conditions and demonstrate the importance of identifying minor precursor events to identify areas of future hazard.

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“…The gross morphology of the region was strongly affected Quaternary glaciations. Well-developed glacial valleys and deep fjords are the dominant landforms (Böhme et al, 2015). The gentle paleic surfaces above deeply incised fjords and valleys with smooth mountain peaks ranging from ~1500 to 1800 m a.s.l.…”

Section: Study Areamentioning

confidence: 99%

Schmidt-hammer exposure-age dating (SHD) performed on periglacial and related landforms in Opplendskedalen, Geirangerfjellet, Norway: Implications for mid- and late-Holocene climate variability

2018

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Schmidt-hammer exposure-age dating (SHD) was applied to a variety of boulder-dominated periglacial landforms in an attempt to establish a local mid-/late-Holocene chronology for the Geirangerfjellet in South Norway. Landform ages were obtained by application of a local calibration curve for Schmidt hammer R-values based on young and old control points comprising fresh road cuts and a bedrock surface in proximity to the study area, respectively. The area was deglaciated ~11.5 ka ago according to independent age information. Investigation of age, formation and stabilization of the periglacial landforms and processes involved allowed assessment of the underlying Holocene climate variability and its relationship to landform evolution. Our SHD ages range from 7.47 ± 0.73 ka for glacially abraded bedrock at the valley bottom to 2.22 ± 0.49 ka for surface boulders of a rock-slope failure. All landforms shared negative skewness and largely have narrow tailed frequency distributions of their R-values. This points to either substantial reworking of the boulders within a landform or continuous debris supply. Our results show that most landforms stabilized during the Holocene Thermal Maximum (~8.0–5.0 ka). The findings do not support the hypothesis that rock-slope failures predominately occur shortly after local deglaciation. Instead, it appears that they cluster during warm periods due to climate-driven factors, for example, decreasing permafrost depth or increasing cleft-water pressure leading to slope instabilities. Periglacial boulder-dominated landforms in the western maritime fjord region seem to react sensitively to Holocene climate variability and may constitute valuable but to date mostly unexplored sources of palaeoclimatic information.

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Analyses of past and present rock slope instabilities in a fjord valley: Implications for hazard estimations

Cited by 44 publications

References 47 publications

Magnitude and frequency relations: are there geological constraints to the rockfall size?

Magnitude and frequency relations: are there geological constraints to the rockfall size?

Evolution of events before and after the 17 June 2017 rock avalanche at Karrat Fjord, West Greenland – a multidisciplinary approach to detecting and locating unstable rock slopes in a remote Arctic area

Schmidt-hammer exposure-age dating (SHD) performed on periglacial and related landforms in Opplendskedalen, Geirangerfjellet, Norway: Implications for mid- and late-Holocene climate variability

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