Item: LESSONS FROM SEVERAL AVALANCHES IMPACTING AVALANCHE PROTECTIVE STRUCTURES IN ICELAND IN JANUARY 2020 AND MARCH 2023
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Title: LESSONS FROM SEVERAL AVALANCHES IMPACTING AVALANCHE PROTECTIVE STRUCTURES IN ICELAND IN JANUARY 2020 AND MARCH 2023
Proceedings: International Snow Science Workshop 2024, Tromsø, Norway
Authors:
- Tómas Jóhannesson [ Icelandic Meteorological Office, Reykjavik, Iceland ]
- Harpa Grímsdóttir [ Icelandic Meteorological Office, Reykjavik, Iceland ]
- Kristín Martha Hákonardóttir [ Verkís Consulting Engineers, Reykjavík, Iceland ]
- Sveinn Brynjólfsson [ Icelandic Meteorological Office, Reykjavik, Iceland ]
- Óliver Hilmarsson [ Icelandic Meteorological Office, Reykjavik, Iceland ]
- Alexander H. Jarosch [ ThetaFrame Solutions, Kufstein, Austria ]
Date: 2024-09-23
Abstract: Seven snow avalanches from two recent avalanche cycles in Iceland, that interacted with snow supporting structures, braking mounds, deflecting dams and catching dams, provide empirical data about the effectiveness of avalanche protective structures. Observations of the avalanches also provide important indications about rest risk in protected settlements. One of the cycles occurred at Flateyri, NW-Iceland, in January 2020. The settlement at Flateyri is protected with two 14–20-m-high deflecting dams with an upstream slope of 40°, and a 10-m-high catching dam, built from unreinforced loose materials. Field observations at Flateyri indicate that the dense core of the avalanches was preceded by a rapidly-moving fluidized front, which overflowed the dams, damaged cars and buildings, and buried a person in snow in her bedroom. The dense core of both avalanches was deflected away from the settlement. The dams channelled the dense core into thick, powerful streams along the dams, and this part of one of the avalanches caused great destruction in the harbour of the village. The other cycle was in Neskaupstaður, E-Iceland, in March 2023 where several snow avalanches interacted with snow supporting structures, braking mounds and catching dams. Field observations and backcalculations indicate that the supporting structures reduced the release volume of several avalanches in this cycle and that the structures, together with braking mounds and dams in the run-out zone, prevented several avalanches from reaching the settlement. Our interpretation of observations from the two avalanche cycles indicates that steep dams and mounds may have more effect than structures with gentlersloping upstream sides on rapid fluidized fronts, preceding some dry-snow avalanches. Channalized streams along deflecting dams need to be taken into account in the revision of hazard zones in areas below deflecting dams where the hazard may be increased at some locations. Rest risk below some avalanche dams in Iceland might be considerable and evacuation plans are needed for the uppermost houses to deal with this risk. Finally, due to the inherent uncertainty associated with avalanche forecasts and decisions on evacuations, permanent mitigation measures are essential for high-risk areas in settlements in Iceland.
Object ID: ISSW2024_O7.4.pdf
Language of Article: English
Presenter(s): Harpa Grímsdóttir
Keywords: Avalanche protection measures, avalanche dams, dam overflow, rest risk, fluidized flow
Page Number(s): 820 - 827
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