2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 196-1
Presentation Time: 8:05 AM


PRESTEGAARD, Karen L., Geology, University of Maryland, College Park, MD 20742, kpresto@umd.edu

E-an Zen paid attention to landscapes. He thought about how the landscape influenced Civil War battles that were fought near his home in northern Virginia. He frequently hiked trails at Great Falls and looked at the bedrock erosion, potholes, strath terraces, and transported boulders. He noticed that boulders on the upper terraces were transported significant distances from their source terrain. He also became interested in the shapes of potholes that he found in the upper terraces of the Potomac and we worked together to determine whether the bucket-shaped potholes we found along bedrock edges were different features than the vertical potholes found on flat surfaces. We concluded that these lateral potholes were formed by vortices with axes in the horizontal, not the vertical plane. The position of these potholes also identified where vortices, spawned from upstream protrusions, impinged on bedrock surfaces. These attachment points of the vortices resulted in lateral pothole erosion, but also provided information on the length of the flow separation zone and thus the flow velocity and Reynolds numbers. I benefited greatly from nearly two decades of discussions with E-an; he was my main discussant as I developed testable hypotheses from field observations and measurements. This is an important step in science and discussants like E-an are true gems in the scientific process.