Date Thesis Awarded
Honors Thesis -- Access Restricted On-Campus Only
Bachelors of Science (BS)
Gregory S. Hancock
James M. Kaste
Mark K. Hinders
The erosion of bedrock-floored channels is a critical process governing the rate of landscape evolution in many settings. Recent numerical modeling of rock-floored channel cross-sections suggests that equilibrium channel geometry and slope are sensitive to variations in rock erodibility, especially along the channel perimeter. However, few field studies have focused on systematic measurement of rock erodibility across bedrock-floored channels. We hypothesize that variations in weathering intensity and duration across some channels results in variable erodibility. To determine if erodibility varies in some channels, we used a Type N SilverSchmidt hammer to measure in situ compressive strength in channels floored by sandstone (3 sites, Utah), granite (1 site, Virginia) and limestone (2 sites, Virginia). Rock strength, which decreases with increased weathering, is assumed to be an adequate proxy for erodibility (Sklar et al., 2001). In four of six channels, average compressive strength decreased 24 – 52% between the waterline and the highest exposed bedrock (1.6 – 3.2 m above the thalweg). In one limestone channel, average compressive strength increased 70% between the waterline and 2.6 m above the thalweg. In a rapidly eroding sandstone channel, erodibility remained constant at all elevations. We used an electron microprobe to conduct chemical weathering and porosity analyses on three of five channels. Observed variation in bedrock erodibility is predominantly caused by weathering, but the extent and dominant form are highly variable, depending on climate conditions and rock type.
Sparacino, Matthew S., "Variability of erodibility in bedrock-floored channels produced by differential weathering" (2012). Undergraduate Honors Theses. William & Mary. Paper 865.
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