River incision into bedrock sets the pace of landscape evolution in most settings and is the mechanism by which tectonic signals are communicated to the landscape. Consequently, a mechanistic understanding of river incision is important for many practical problems (e.g., river restoration, habitat stability) as well as for addressing intellectual questions such as how will a landscape respond to an increase in tectonic uplift rate or annual precipitation? In the past decade, recognition of the importance of bedrock river incision has led to an explosion of research on this topic, and substantial progress has been made in understanding river incision processes. However, most efforts have treated rivers one-dimensionally. Hence, how a river erodes laterally in a valley is largely unknown. Consequently, features such as bedrock (strath) terraces, which illustrate the alternating dominance of lateral and vertical incision over geologic time-scales, remain enigmatic. A deeper understanding of how bedrock terraces form would illuminate lateral erosion mechanics and would help answer a century-old question in Geomorphology, how and why do rivers form terraces in bedrock? This project, which combines numerical modeling, analysis of high resolution topographic data, and field work focused on the Smith River in Oregon and on the Pescadero Creek watershed in California, will test hypotheses related to how and why rivers move laterally across bedrock, and the consequences of this for where and when terraces form.
Broader Significance: Through better understanding of processes of lateral bedrock erosion, we can test the plausibility that bedrock rivers might record climatic or tectonic events when they create terraces. This is of fundamental scientific value because the record rivers leave in the landscape is one of the few direct clues that we have to understand how landscapes respond to shifting climates. This research will also foster invaluable scientific training for a PhD student, an undergraduate research assistant, and an entire undergraduate geology class that will be involved in field-testing the hypotheses articulated in the proposal.
