Date of Award

12-2020

Degree Type

Report

Degree Name

Master of Science (MS)

Department

Geosciences

Committee Chair(s)

Tammy Rittenour (Committee Chair)

Committee

Tammy Rittenour

Committee

Kelly Bradbury

Committee

Joel Pederson

Abstract

Over 2.6 million people travel along highway SR-12, a National Scenic Byway, through Bryce Canyon in southern Utah each year. This highway is a major thoroughfare for tourists traveling to Bryce Canyon National Park, Grand Staircase-Escalante National Monument, and other scenic attractions. SR-12 is susceptible to rockfall and landslide hazards where it descends from the Paunsaugunt Plateau into Tropic Canyon, and these hazards have potential consequences of economic loss due to travel delays for tourists and commodities, and possible loss of life. Rockfall could have devastating effects at this location because of the traffic volume, sharp turns, low visibility, and steep drop-offs. A landslide on SR-12 in 2017 prompted emergency repairs that cost over $2.6 million dollars. SR-12 runs below a cliff band of the relatively weak limestones and mudstones, the Tertiary Claron Formation, that make up the colorful hoodoos and erosional features of Bryce Canyon. The Oligocene- to Miocene-aged Ruby’s Inn Thrust Fault has juxtaposed a resistant, cliff-forming Claron layer on a weak, slope-forming layer of the Claron Formation, creating the potential for rockfall that could impact the roadway and associated travel. The research hypothesis of this project is that the Ruby’s Inn Thrust Fault and associated fracturing have weakened the rocks in this cliff band creating a rockfall hazard. Research objectives are 1) to characterize cliff-forming lithologies within the study area; 2) to examine the fracture characteristics in cliffs using scanline techniques; 3) to measure the topography and assess physical properties of the toe slope; and 4) to assess rockfall potential and identify contributing factors for hazards posed by this cliff band in between SR-12 milepost markers 15 and 15.7. Field data collected included linear scanlines along the thrust fault and at a control location site, sample collection, contact geologic mapping, and lithologic unit descriptions. Laboratory testing was performed to assess physical characteristics of the rock, soil, and fracture infillings. These data are used for kinematic analyses of the cliff band to assess failure potential. Rockfall analyses were also performed to assess the probability of rocks reaching the roadway after failure.

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