Item: START-ZONE TERRAIN AND THE OCCURRENCE AND TIMING OF WET SLAB AVALANCHES IN COLORADO
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Title: START-ZONE TERRAIN AND THE OCCURRENCE AND TIMING OF WET SLAB AVALANCHES IN COLORADO
Proceedings: Proceedings, International Snow Science Workshop, Whistler, BC, Canada, 2026
Authors:
- Brandon Levy [ Colorado Avalanche Information Center, Leadville, CO, USA ]
- Ron Simenhois [ Colorado Avalanche Information Center, Leadville, CO, USA ]
- Erich H. Peitzsch [ U.S. Geological Survey, Northern Rocky Mountain Science Center, West Glacier, MT, USA ] [ Montana State University, Department of Earth Sciences, Bozeman, MT, USA ]
- Ethan Greene [ Colorado Avalanche Information Center, Leadville, CO, USA ]
Date: 2026-09-28
Abstract: Wet slab avalanches (WSAs) release when liquid water reduces the strength of a buried weak layer or interface, and their timing is governed primarily by the snowpack energy balance and the movement of meltwater. We classified 717 WSAs from the Colorado Avalanche Information Center database (2011–2025) into five start-zone terrain categories and analysed the timing of naturally triggered, near- and above-treeline events using rank-based and Bayesian hierarchical methods. Start-zone terrain strongly governs the natural occurrence of WSAs: approximately 64% released in Rocky start zones (Cliffs/Rocks), while only ≈4% occurred on Open Slopes. After controlling for latitude and aspect, Rocky start zones released approximately five days before Open Slopes (90% CrI: 0.6–9.9 days). Latitude was the dominant timing predictor, shifting release by roughly 3–4 weeks from southern to northern Colorado. Cornice start zones concentrated WSA activity in early to mid-spring, with 40 of 41 releasing before mid-May. These findings support start-zone terrain classification as a low-cost addition to observation protocols for improving the spatial targeting of wet slab outlooks.
Object ID: ISSW2026_P2.24.pdf
DOI: https://doi.org/10.15788/1790098944
Language of Article: English
Presenter(s): Ron Simenhois
Keywords: wet slab avalanche, start zone, terrain classification, release timing, Bayesian hierarchical model, Colorado
Page Number(s): 913 - 920
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