Item: SHALLOW BUT STILL LONG: PECULIAR AVALANCHE ACTIVITY IN NORTHERN NORWAY
-
-
Title: SHALLOW BUT STILL LONG: PECULIAR AVALANCHE ACTIVITY IN NORTHERN NORWAY
Proceedings: Proceedings, International Snow Science Workshop, Whistler, BC, Canada, 2026
Authors:
- Matrin Ahrland Stefan [ Wyssen Avalanche Control AS, Norway ]
- Holt Hancock [ Norwegian Geotechnical Institute, Norway ]
- Peter Gauer [ Norwegian Geotechnical Institute, Norway ]
Date: 2026-09-28
Abstract: Between December 3rd and 4th, 2025 some peculiar natural avalanches occurred in Tverrbotn adjacent to the Andersdalen valley, approx. 20 km south of Tromsø in Northern Norway. Weather preceding the event included modest (<20 cm) snowfall amounts accompanied by light to moderate southeasterly winds at ridgetop . This snow fell on a stable snowpack with locally weak, lightly faceted snow surfaces, developed during a period of colder, clear weather in the days prior. Limited avalanche activity was reported in the region following the snowfall, with a single thin, wide crown on a southwest aspect at 900 m serving as a notable exception. Upon investigation of this crown on December 7th, observers discovered multiple soft slab avalanches in an adjacent drainage that had in places ran 6-700 m to the valley floor. These avalanches had very thin crowns (5 to 10 cm) and were accompanied by extensive cracking that propagated into lower-angle terrain, indicating high fracture propagation potential. Our curiosity was piqued for two reasons. First, our experience led us to believe that the regional weather patterns preceding the event rarely produce noteworthy avalanche activity. While weather and snow conditions specific to the investigated drainage may have controlled these avalanches, they were subtle enough to be no longer evident under observation several days post-event. Second, relatively minor new-snow accumulations and thin slabs nevertheless resulted in comparatively long runouts. Simulating these avalanches can help illustrate how interactions among slab characteristics, propagation potential, and entrainment allow even thin, soft slabs to reach long runouts. We hope this case study illustrates how the analysis of unusual, but by no means extreme, avalanche events can contribute to improved avalanche forecasting in situations characterized by high spatial variability. It also demonstrates how simulation tools can be used to investigate the processes that allow relatively thin slabs to produce unexpectedly long runouts.
Object ID: ISSW2026_P4.26.pdf
DOI: https://doi.org/10.15788/1790099310
Language of Article: English
Presenter(s): Holt Hancock
Keywords: shallow avalanches, field observations, avalanche modeling.
Page Number(s): 1078 - 1083
-