The influence of lithology on the forms of hillslopes and drainage basins in soil mantled landscapes
Abstract/Contents
- Abstract
- Much of the Earth's surface is blanketed by a mantle of soil and weathered rock. In these settings, topographic forms are typically smooth, with convex hillslopes grading subtly into the concave valley networks that define drainage basins. In 1877, G.K. Gilbert recognized that this smooth topography masked the underlying variability in geologic structure and proclaimed this the `Law of Divides.' Gilbert reasoned that in settings where rock weathered to soil faster than that soil could be eroded, topographic forms would be dictated by the processes transporting that soil rather than the variations in strength of the underlying rocks. There are exceptions to every rule, and this dissertation focuses on exceptions to Gilbert's `Law of Divides, ' situations where lithology influences the form of soil-mantled landscapes. I begin at hillslopes, demonstrating that if soil transport is sensitive to soil thickness, which in turn depends on underlying rock properties, variations in hillslope gradient can arise at geologic contacts, a phenomenon observed in some landscapes. Following this, I focus on the heads of valley networks and ultimately entire drainage basins. In the Gabilan Mesa, in the central Coast Ranges of California, properties of the weathered zone vary with slope aspect, placing rocks that favor headward channel growth close to the surface on south facing slopes. As a result, the preferential expansion of channel heads on south-facing slopes has led to a basin-scale topographic asymmetry. I conclude by measuring asymmetry in drainage basins in a number of other landscapes, and demonstrate that asymmetry in the structure of drainage networks is most pronounced in rock types that may be especially vulnerable to erosion. Hence, even at the largest scales, soil-mantled topography may encode some signature of the properties of underlying rocks.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2016 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Johnstone, Samuel Adam |
|---|---|
| Associated with | Stanford University, Department of Geological Sciences. |
| Primary advisor | Hilley, George E |
| Thesis advisor | Hilley, George E |
| Thesis advisor | Finnegan, Noah J |
| Thesis advisor | Graham, S. A. (Stephan Alan), 1950- |
| Advisor | Finnegan, Noah J |
| Advisor | Graham, S. A. (Stephan Alan), 1950- |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Samuel Adam Johnstone. |
|---|---|
| Note | Submitted to the Department of Geological Sciences. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2016. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2016 by Samuel Adam Johnstone
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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