Stability Changes After Weak Layer Collapse near Beehive Basin, Montana, USA, March 2026

The USGS Northern Rocky Mountain Science Center, in collaboration with the Department of Earth Sciences, Montana State University, collected Propagation Saw Tests (PSTs) on a slope near Beehive Basin, Montana, before and after the snowpack collapsed unexpectedly. We also analyzed videos of these tests to measure weak layer collapse heights. A PST is a snowpack test that estimates crack propagation propensity. It involves isolating a column of snow and dragging a snow saw along the weak layer uphill to initiate a fracture (American Avalanche Association, 2022). Understanding propagation propensity, and how it changes after a collapse, is key for assessing snowpack stability. Avalanche practitioners, including ski guides, ski patrollers, and avalanche forecasters, make decisions based on their assessments of snowpack stability. Snowpack collapses, often referred to as “whumpfs,” are considered a clear sign of snowpack instability in the surrounding terrain, but the stability of the collapsed slope itself is less certain. Thus, this dataset improves our understanding of changes in propagation propensity following weak layer collapse. Further, video analysis of these snowpack tests allows us to measure changes in collapse height. Collapse height provides information about the thickness of the weak layer and helps us begin to understand how much energy is available in the snowpack to drive crack propagation. The dataset includes PST results as well as results from our video analysis. The dataset provides insight into changes in stability of one snowpack weak layer, at one time, and cannot be generalized to other scenarios.