RUI: Quantifying the effects of wildfire burning on 10Be concentrations in river sand - A study of the 2018 Woolsey Fire, Santa Monica Mountains, CA

Eastern Michigan University, Ypsilanti MI

Investigators

Abstract

The rates at which landscapes evolve over hundreds to thousands of years – geological erosion rates – provide important information about landscape stability, rates of sediment erosion or movement, seismic motion on faults, and the magnitude of human-caused erosion above background geological erosion. Exactly how geological erosion rates are affected by short-lived but large-magnitude erosive events such as floods, hurricanes, earthquakes, landslides, and wildfires remain poorly understood. This project focuses on the Woolsey Fire, which burned through ~100,000 acres of the Santa Monica Mountains, southern California, in November 2018. The Woolsey fire provides a unique opportunity to understand how a short-duration, large-magnitude fire disrupts and changes geological erosion rates owing to an existing dataset of pre-fire erosion rates determined in 2016. Through this project, three undergraduate research students will receive personalized training in Earth science research, analyze real-world data for senior theses, and learn how Earth’s surface changes in response to wildfires. Geological erosion rates have been determined for thousands of rivers around the world by measuring the concentration of 10-beryllium (10Be) in quartz river sand. Measured 10Be concentrations are only produced in Earth’s near-surface and are thus sensitive to or diluted by short-lived deep-erosion events such as gully erosion, landslides, and debris flows, all of which are common following wildfires. The effect of post-fire erosion on measured 10Be concentrations is largely unknown because it is rare to have existing 10Be data from rivers that are subsequently affected by severe burning. This project benefits from a 10Be dataset collected from seven rivers draining the Santa Monica Mountains in 2016, two years prior to the 2018 Woolsey Fire. Four of these rivers were completely burned by the fire, providing the unique opportunity to (1) quantify how much measured 10Be concentrations in river sand have changed as a result of wildfire-caused erosion in burned catchments and (2) quantify the reproducibility of 10Be concentrations in unburned catchments. This project will have a clear and beneficial impact for the growing number of scientists who use 10Be data in their work because it serves to provide one of the first long-term, systematically-collected 10Be replicate sample sets in a steep, semiarid, fire-prone landscape. Because 10Be-derived erosion rates are used to contextualize modern human-induced sediment runoff, map seismic activity in tectonically-active regions, and assess landscape stability over geologically-meaningful timescales, this work will broadly benefit a wide range of professionals who rely on geomorphologists’ ability to produce accurate and informative interpretations of sediment transport and landscape evolution. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.