What is it about?
The unstable rock-slope Mannen in western Norway is classified as a high-risk object, with the possibility of the failure of a 20Mm3 large rock-avalanche. Several rockslide depositis in the valley bottom below the rock-slope instability indicate a high previous rock-slope failura activity. Based on detailed mapping and surface exposure dating (10Be), two temporal clusters were indentified. At least three rock-avalanches impacted the valley shortly after local deglaciation, while another cluster of 3-6 rockslides suggests high rock-slope failure activity at the end of the Holocene Thermal Optimum. The Quaternary geology in the valley bottom tells a complex and interesting history of glaciation, deglaciation, sea-level fall and rock-slope failure activity.
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Why is it important?
We identified a Holocene cluster of rockslides where the same slope failed three to six times within less than 200 years, which has never been shown with such precision before. We show therefore that the series of historical rock-avalanches in the 20th century at the Norwegian Loen site which have been the most deadly natural hazards in Norway is not an individual case. Our results show a close correlation of rock-slope failures to climatic conditioning which has rarely been discussed in Norway previously. Both, the multiple failures and the climatic correlation are critical factors for risk assessments and potential failure scenarios for unstable rock slopes in Norway and worldwide. Multiple slope failures from one slope have been reported rarely at all and at other locations (Andes) been related rather to tectonic activity.
Perspectives
Working at this study site together with collegues from different research fields and areas was an incredible experience. New elements were discovered during every field visit, not only clarifying but also making the story more complex. The results are highly interesting and hopefully this publication will inspire other researches in their projects and enhance the discussion about multiple rock-slope failures from one slope, triggered not by earthquakes but by internal stress re-organisation and climatic impacts.
Paula Hilger
Western Norway University of Applied Sciences
Read the Original
This page is a summary of: Multiple rock-slope failures from Mannen in Romsdal Valley, western Norway, revealed from Quaternary geological mapping and 10Be exposure dating, The Holocene, September 2018, SAGE Publications,
DOI: 10.1177/0959683618798165.
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