Abstract

Potholes are depressions that have been carved out of bedrock. For this research project, we studied the 50 potholes on the top of Rock Window Mesa in Chinle Valley, AZ. Our first goal was to understand the processes currently affecting the addition or removal of pothole sediments. Our second goal was to understand pothole formation. While studying pothole sediment removal, we discovered that the wind speed threshold for deflation in the potholes is about 50 km/h, independent of pothole size. We conclude that deflation is the reason potholes don’t fill with sediment. In our study of pothole formation, we analyzed a high-resolution orthophoto and a DEM of the mesa’s topography with cm-scale resolution. We used these data, in conjunction with the data we collected in the field, to produce a geomorphological map of the mesa. We found a number of interesting trends in the pothole data. The pothole-forming processes appear to favor rounder, smaller, shallower potholes relative to the size distribution of the potholes, and they favor the southern and western edges of the mesa. The potholes show three preferred orientations, they generally ignore structural features, and they disrupt drainage systems. The processes that formed the potholes may also be responsible for the ubiquitous erratic pebbles and cobbles on the mesa. We observed the processes of pedogenesis, spalling, and deflation acting on the mesa and in the potholes. Repeated cycles of these processes may enlarge the potholes, but our data indicate fluvial origin. The literature points to two possibilities: 1) during the Late Miocene/Pliocene, the surface of Rock Window Mesa was in or near a paleodrainage, and the potholes were carved out by flash flooding during those epochs, and 2) that the top of Rock Window Mesa is a remnant of an over-steepened tributary junction. These possibilities account for the formation of the potholes in ways that are well understood, and explain the erratic pebbles and cobbles, the lack of joint control, the requirement that pothole formation proceed at a faster rate than erosion caused by annual monsoon rains, the morphologies of the potholes, and the preferred pothole orientations.

LLU Discipline

Earth Sciences

Department

Earth Science

School

School of Medicine

First Advisor

Leonard Brand

Second Advisor

Cornelis Bootsman

Third Advisor

H. Paul Buchheim

Fourth Advisor

Ronald Nalin

Fifth Advisor

Kevin Nick

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

2018

Date (Title Page)

6-2018

Language

English

Library of Congress/MESH Subject Headings

Geomorphology; Potholes

Type

Dissertation

Page Count

xiii, 141 p.

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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