Investigating linear patterns in the Sierra Nevada (USA) and developing an empirical relationship between erosion rate and fracture concentration

Richard A. Becker
University of Wisconsin-Madison, Department of Geoscience Madison, Wisconsin 53706 USA
[email protected]

It has been known for over 100 years that pre-existing joints and fractures exert significant influence on geomorphology and landscape evolution. Over this time period many studies have confirmed that fracture matter, but none have determined how much they matter. This is one of the principal aims of my research: to quantitatively assess the importance of pre-existing fractures to landscape evolution. Funds provided by AAPG have enabled the collection of rock samples for ¹⁰Be surface exposure dating from the John Muir Wilderness of the Sierra National Forest and the Tuolumne Meadows area of Yosemite National Park. ¹⁰Be concentration – a proxy for erosion – will be correlated with outcrop and map-scale fracture concentrations to produce scatter plots. Regression analysis will be used to determine the importance of fracture concentrations to erosion rates (the slope of the regression line) and the confidence that we can have in this assessment of importance (the degree of scatter around that line). In addition, as a secondary assessment, fractures are being digitized off aerial photographs at a 1:10,000 scale. The average fracture concentration over ~1 km² areas with uniform lithology and outcrop exposure will be compared with similar areas in order to look for a statistically-significant relationship between fracture concentration and slope.

AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects