Masters Thesis

Near-surface geophysical imaging of the internal structure of el capitan meadow rock avalanche in yosemite national park, california

Rock avalanches are a large form of mass movement which, while uncommon, are particularly destructive due to their very high volumes and long flow distances. Due to their rarity, they are typically studied well after they occur. Mass movement events can subject humans to risks and casualties as well as cause massive infrastructural damage. The El Capitan Meadow rock avalanche lies at the foot of El Capitan in Western Yosemite Valley. I investigated this avalanche using Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) to image the internal structures, depth, and topography of the underlying paleo-surface of the valley. GPR and ERT surveys were conducted along three profile lines over the avalanche deposit. ERT results showed a strong but gradual resistivity contrast between the low resistive soil of the prior valley surface and the highly resistive rock avalanche deposits, however, detecting the interface with precision was difficult. GPR results revealed several sharp interfaces within the subsurface making it impossible to identify which one was the interface to the valley floor. Selected interfaces from the GPR model were incorporated into the ERT inversion process, where the GPR interfaces, which indicated the true location of the valley floor, was the one which produced the sharpest resistivity contrast in its ERT model. At the intersection points of the profiles, the estimated depths to the paleo-valley floor had similar elevation revealing a flat extension of the exposed valley floor beneath the rock avalanche deposits.

Items in ScholarWorks are protected by copyright, with all rights reserved, unless otherwise indicated.