RAPID: Documenting the temporal variance of the isotopic signature of detrital sediments following massive stochastic events using Hurricane Maria as a case study

Oberlin College, Oberlin OH

Investigators

Abstract

Hurricane Maria's direct hit on Dominica caused thousands of landslides and debris flows that coursed down stream beds and poured sediment into coastal waters. Such massive and episodic sediment erosion and transport is important both as a geologic hazard affecting communities on the island, and because the impact of rare events on erosion rates determined from isotopic tracers measured in detrital sediment remains a major uncertainty in these methods. The scientific team is in a unique position to quantify the effect of this catastrophic storm on the utility of detrital sediment as a landscape-scale erosion monitor, having collected fluvial sediment from 31 sites on Dominica in June 2017. By resampling these sites as soon as practical, they can compare nuclide activities in sediment before and after the major change in surface process regime occasioned by the storm. Flights to Dominica route through Puerto Rico, allowing the team to also resample the Luquillo area, thereby obtaining post-storm data for all 10Be-derived erosion rate sites in the Caribbean. Using remotely-sensed images as a guide, the team will measure volume, thickness, and extent of selected storm-related deposits. The team will work with a researcher at the University of the West Indies (the institution responsible for natural hazard management on the English-speaking islands), and with the Dominica disaster management office, using their network to reach the wider community. Two undergraduates will be involved in field work, will engage with the local researcher, and will analyze data for their senior theses. It is challenging to find natural experiments that give clear information about temporal variability in isotopic concentration of sediment caused by pulses of material moving through the sediment system. the researchers propose to collect sediment to be analyzed for in situ and meteoric 10Be, 210Pb, 137Cs, and 7Be to infer both the depth of erosion and sediment sources, defining the temporal and spatial variance of nuclide concentration in fluvial sediment. The samples collected will provide valuable information about the effects of episodic erosion, particularly landslides, on the concentration of nuclides used to interpret erosion rates over space and time, a long-standing issue. These methods have been widely applied at thousands of sites around the world but the effects of large, stochastic events on the data have rarely been tested. The opportunity to sample immediately following an unusually intense storm allows for better understanding of the frequently observed mismatch between measures of erosion that integrate over different times - short-time period data often do not capture major events that, when integrated over geologic time, drive erosion rates. Hurricane Maria provides an ideal natural experiment for understanding temporal variability in erosion and sediment yield due to a single event.