Dr. Allison Pfeiffer
Western Washington University

Topic: From rock strength to river response: Bed material abrasion controls on downstream cascading hazards from crumbling volcanoes

Academic Host: Greg Tucker

Abstract: Large sediment pulses from stratovolcanoes are an increasingly frequent hazard, as climate change-induced thawing of rock permafrost accelerates catastrophic alpine mass wasting events. Beyond the initial impact, the vast quantities of sediment deposited in river channels can trigger cascading hazards, including downstream channel aggradation and increased flood risk. However, our field has yet to construct a comprehensive framework for predicting the magnitude and timing of these fluvial responses. In this talk, I hope to convince you that bed material abrasion of potentially weak volcanic sediment is a key control on these downstream impacts. I will present field datasets that characterize the variability in sediment characteristics sourced from volcanic mass wasting events from sites across the Pacific Northwest, and the results of numerical models exploring the controls on their downstream effects.

These findings have implications beyond stratovolcanoes, as highly abradable lithologies are not unique to volcanic settings; many common sedimentary rocks, for example, are equally or even more susceptible to abrasion. Ultimately, our work shows that forecasting landscape response to major disturbances will require a framework that integrates lithology and its fundamental control on bed material abrasion and grain size.