92-5 Using Landslides of the Cispus River Watershed near Mount Adams, Washington, to Date Glacial and Volcanic Events

Session: Landslide Inventory Mapping and Next Steps: Assessing Susceptibility, Hazard Models, Risk, and Policy

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Surface roughness is a key parameter for mapping and describing geologic landforms like landslides. By facilitating downslope transport from hillslopes, landslides disturb the landscape into which they move and thereby leave a rougher topography than their surroundings. Over time, the landslide gradually weathers into the contours of the environment, making surface roughness useful for identifying youthful landslides and tracing their evolution through time. Surface roughness as a proxy for age has been successfully used in both landslide and more recently lava flow applications, yet the methodology and its potential limitations requires continued research. This study examines landslides along the Cispus River and nearby watersheds near Mount Adams, Washington, to test the usability of existing calibration dating techniques. The landslides fall into two categories. Most are bedrock landslides derived from the Oligocene to Miocene volcanic bedrock. The remaining landslides are shallower, commonly associated with landslide-initiated debris flows, and likely derive from glacial deposits. Both types of landslides commonly overly glacial drift and what have traditionally been interpreted as outwash terraces, while a few landslides are cross-cut by the terraces. Applying calibrated surface roughness dating to these landslides can establish landslide recurrence intervals and constrain ages of glacial and volcanic events in these watersheds. However, this study highlights some potential challenges in applying this calibrated dating technique, including: 1) the methodology assumes landslides are single events but does not account for the possibility of reactivation of existing failures, 2) the methodology may give anomalously old ages for landslides that have erosion and redeposition along the landslide’s toe, and 3) the methodology does not currently address the role of climate or changing climate conditions through time. Continued research should prioritize strategies to account for these variables so that the tool may be more broadly applicable for reconstructing regional landslide histories and associated hazard assessments.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9855

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