Publication Date

Fall 2018

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

Advisor

Emmanuel Gabet

Keywords

granite, joint, rock strength, Schmidt hammer, topography, Yosemite

Subject Areas

Geology; Geomorphology; Petrology

Abstract

Although contrasts in rock strength correlate to variations in topography, the role of rock strength in shaping the landscape of Yosemite National Park is uncertain. Magmatic processes may create variations in mineralogy within a single plutonic unit, while tectonic processes may result in contrasts in joint density and foliation, all of which may lead to variations in rock strength. For this study, the relationship between differences in mineralogy, joint density, and foliation in Yosemite National Park is analyzed to determine the role of rock strength in shaping Yosemite’s topography. Modal mineral abundance and grain size are determined by analyzing cut rock samples, while joint density and foliation intensity are recorded at 83 sites. Also, a Schmidt hammer is used to compare rock strength readings to elevation at all 83 sites. This study finds that variations in joint density shape many topographic features, including Mount Hoffman, a topographic high point in Yosemite. High potassium feldspar and low plagioclase abundance may also be a factor in Mount Hoffman’s erosion resistance. No significant relationship between foliation and other factors is observed. Schmidt hammer readings typically increase with elevation, which is likely a result of weathering differences. Decreasing joint density across Yosemite National Park is found to be associated with decreased forestation. Overall, while few correlations are observed across the entire landscape, rock strength shapes the landscape of Yosemite at varying scales.

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