Failure ages of ancient rock avalanches in the Intermountain Seismic Belt of northern Utah

Abstract:

Large rock slope failures are important contributors to landscape evolution and geologic hazards in tectonically active regions. Northern Utah, within the Intermountain Seismic Belt of the western United States, contains deposits of several large, rapid- and long-runout ancient rock avalanche events, however the majority of these have not previously been dated. While earthquakes and climate change are often implicated as triggers for slope failures identified in the geologic record, detailed chronological control is necessary to develop a convincing mechanistic linkage. Here we present failure chronologies for six of the largest rock avalanches in northern Utah derived from in situ cosmogenic ¹⁰Be and³⁶Cl exposure ages as well as radiocarbon dating. We contrast rock avalanche failure ages with paleoseismic chronologies from nearby fault systems and regional paleoclimate records in order to assess potential triggering factors. The rock avalanche failure ages presented here, combined with new assessment of event volumes, are critical for assessing the hazard posed by these rare large rock slope failures and their importance in landscape evolution.