6 Surficial geology and neotectonics in the West: Celebrating and advancing the legacy of Kirk Bryan through field-based geomorphology studies (Posters)

This session invites and examines recent field-based geomorphology studies in the West. Contributions regarding soils geomorphology, neotectonics, pediments, fluvial terraces, and landscape development are invited.

Monday, 18 May 2026
8:00 AM - 5:30 PM
Alvarado D/E

Hillslope Connectivity in Yellowstone National Park: Debris Flows and Alluvial Fan Deposition During an Extreme Rain On Snow Event

Paper number: 6-4
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Hillslope connectivity is a critical aspect of understanding the movement of sediment from source to sink, particularly in landscapes prone to mass movements and frequent precipitation events. The northeast portion of Yellowstone National Park (YNP) includes high-relief mountainous terrain of the Beartooth Uplift where hillslope sediment movement is dominated by debris flows. In June of 2022, northern YNP experienced an extreme rain-on-snow event which caused significant channel bank erosion and debris flows. We studied four drainage basins in northern YNP: Soda Butte Creek, Slough Creek, the Upper Lamar River, and the Gallatin River to compare how sediment connectivity is related to debris flow deposition on alluvial fans. We modelled the hillslope connectivity using an index of connectivity (IC) that estimates how likely sediment is to be moved from hillslopes onto alluvial fans and compared it to a DEM of difference produced from pre and post-flood LIDAR data.. After assessing the connectivity models predictive capability, we determined that sediment connectivity modelling can be useful in high elevation drainage basins as a tool to predict where erosion might occur and which alluvial fans are likely to be active. We found that there were many slopes with high connectivity values that did not experience failure during the 2022 flood and many alluvial fans that did not experience deposition. The IC provides numerical values to quantify the degree of connectedness between source and sink, but requires verification with high resolution DEMs, airphotos, and field assessments. Because the IC did not accurately predict sediment movement on hillslopes, extreme precipitation during rain-on-snow events might not be when the majority of mass movements occur. To initiate more widespread slope failures, slope destabilization by forest fires or longer duration precipitation events, which did not take place in 2022, may be required

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410634

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