EAGER: Deciphering boulder movement history using cosmogenic isotopes - a numerical investigation.

California Institute Of Technology, Pasadena CA

Investigators

Abstract

We currently lack quantitative field metrics to decipher how often boulders move by fluvial or debris flow processes. This project aims to develop and run numerical experiments to test whether the frequency of boulder movement can be deciphered from cosmogenic exposure dating. Preliminary modeling has shown that, in some cases, the number of boulder movement events can be determined from the pattern of exposure around the circumference of a boulder. The proposed work would include systematic investigation of likely controlling variables (e.g., boulder size, erosion rate, and inheritance) on the mean and spatial variance in nuclide concentration around and within a mobile, eroding boulder. Results from this effort would form the backbone for future field sampling campaigns aimed at measuring boulder movement, potentially applicable to a wide range of environments (e.g., river channels, debris flow fans, moraines). Boulders line the beds of many rivers and are an important control on rates of landscape evolution, yet their long-term behavior is not well understood. The recurrence interval of large, boulder-mobilizing events is often beyond the historical record, leaving the probability of these events poorly constrained. The project aims to improve our ability to predict the frequency of boulder moving events for hazard mitigation and habitat restoration. It could potentially lead to the ability to quantify infrequent, large magnitude flood and debris flow events with recurrence intervals greater than ~ 1000 yrs, which can cause significant loss of life and property.