Item: A VERY LARGE WET SLAB AVALANCHE SURPRISED US, WHICH IS FUNNY BECAUSE THE SAME THING HAPPENED 31 YEARS EARLIER
-
-
Title: A VERY LARGE WET SLAB AVALANCHE SURPRISED US, WHICH IS FUNNY BECAUSE THE SAME THING HAPPENED 31 YEARS EARLIER
Proceedings: Proceedings, International Snow Science Workshop, Whistler, BC, Canada, 2026
Authors:
- Tully Hamer [ Alyeska Resort Ski Patrol, Girdwood, AK, USA ]
- Sean Fallon [ Alyeska Resort Ski Patrol, Girdwood, AK, USA ]
- Jeff Bristow [ Alyeska Resort Ski Patrol, Girdwood, AK, USA ]
- Aleph Johnston-Bloom [ Alyeska Resort Ski Patrol, Girdwood, AK, USA ]
Date: 2026-09-28
Abstract: Wet slab avalanches at Alyeska Ski Resort in Girdwood, Alaska, have historically caused significant infrastructure damage and are among the most unpredictable. Our literature review, spanning decades of observation and research, illustrated that the avalanche industry has identified common ingredients of wet slab avalanches and emphasized that many of these ingredients may be present without an avalanche occurring. Reardon and Lundy's 2004 wet slab conceptual model provided a helpful framework for analyzing these forecasting challenges. We present a case study of two very similar, significant wet slab avalanches at Alyeska, separated by 31 years. In April of 2024, a very large, unexpected wet slab (R4, D4) necessitated extensive terrain closures and operational impacts at Alyeska Resort. A snowcat grooming at night triggered the avalanche that started in closed, gated terrain and flowed across multiple groomed runs. Despite its magnitude, the avalanche caused no injuries or damage to infrastructure. Looking back to April of 1993, a nearly identical avalanche occurred. In an attempt to make sense of the 2024 event, we compared the snowpack and weather for the 1993 and 2024 avalanches. In addition, we applied the wet slab conceptual model as a valuable tool to qualify the wet slab hazard leading up to both the 1993 and 2024 avalanches. Finally, we discuss updating our team's collective mental model for forecasting wet slabs. We gained a more nuanced understanding of monitoring a base area stream gauge and recognizing the presence of a hydraulic barrier within the snowpack. This analysis also highlighted a heuristic trap that we believe is unique to ski area avalanche mitigation. The recognition of which may help shift our hazard reduction mindset for the future. We hope our insights may be useful to practitioners who may be dealing with wet slab avalanches more frequently in a warming climate, or in another 31 years.
Object ID: ISSW2026_O11.1.pdf
DOI: https://doi.org/10.15788/1790098506
Language of Article: English
Presenter(s): Tully Hamer
Keywords: Wet slabs, operational forecasting, crusts, mental models
Page Number(s): 154 - 161
-