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Unraveling the Mysteries of Asymmetric Topography at Gabilan Mesa, California
Author(s) -
Richardson P. W.,
Perron J. T.,
Miller S. R.,
Kirchner J. W.
Publication year - 2020
Publication title -
journal of geophysical research: earth surface
Language(s) - English
Resource type - Journals
eISSN - 2169-9011
pISSN - 2169-9003
DOI - 10.1029/2019jf005378
Subject(s) - asymmetry , geology , mesa , microclimate , geomorphology , erosion , channel (broadcasting) , terrain , aggradation , structural basin , physics , fluvial , geography , computer science , programming language , cartography , archaeology , engineering , quantum mechanics , electrical engineering
We investigated the potential causes of topographic asymmetry at Gabilan Mesa, CA, a site that exhibits large aspect‐dependent differences in hillslope gradients and microclimates. Competing hypotheses have been proposed to explain the asymmetry observed at Gabilan Mesa. One hypothesis states that different microclimates on opposing slopes are responsible for differences in runoff or soil strength, which generates asymmetric topography. A second hypothesis states that differences in sediment flux from opposing slopes causes southward lateral channel migration and oversteepening of north facing slopes. To test these hypotheses, we carried out numerical modeling experiments, terrain analysis, and field measurements. We also considered the role of initial tilting in causing the asymmetry. We found that saturated hydraulic conductivity is considerably lower on south facing slopes in one highly asymmetric basin. This is consistent with the hypothesis that aspect‐dependent runoff is responsible for the asymmetry. We also used cosmogenic radionuclide‐derived erosion rates and topographic characteristics at Gabilan Mesa to test predictions from numerical landscape evolution models that incorporate asymmetry‐forming mechanisms. The aspect‐dependent models reproduce the erosional and topographic characteristics of Gabilan Mesa better than the lateral channel migration model. We conclude that aspect‐dependent runoff is the most likely explanation for most of the topographic asymmetry at Gabilan Mesa. Our results do not rule out tilting as a possible influence on the initial development of asymmetry nor do they rule out the possibility that lateral channel migration has contributed to the asymmetry, but we suggest that tilting and lateral channel migration are not primarily responsible for it.