Abstract: Transience Along a Passive Margin

The Appalachian Mountain range is one of the most interesting geologic features of the American East Coast. Lying along a now passive margin, the Appalachians span a vast array of states from Maine down through Georgia. Their formation began over 480 million years ago with major tectonic events ending during the last 200 million years. Yet, even without significant tectonic forcing, the Appalachians have remained relatively rugged with relief as much as 2000 meters in some portions of its expanse (Miller et al. 2013). Various explanations have emerged over the past century to explain this relief – and the current state of the mountain range – and there has been growing consensus among Geologists that the Appalachians are in a state of disequilibrium (Hack, 1960; Gallen et al., 2011; Hancock & Kirwan, 2007; Miller et al., 2013). My goal is to continue to examine the current state of the Appalachians and postulate causes for its rugged relief. I will be studying an area within the Montebello region of the central Blue Ridge in Virginia.
Recent research methods have opened up new pathways to analyze this ancient orogeny. My research will use two of these new methods, hillslope analysis (using GIS and related software) and calculating erosion rate using cosmogenic radionuclide concentration measurements. The former method involves manipulating Digital Elevation Models in ArcGIS to look for knick-zones in the topography (areas with dramatic changes in steepness). Recent research along the Appalachians has found evidence of knick-zones (Gallen et al., 2011). Finding and identifying these areas, allows one to delineate between relict and recently eroded topography. Analysis also allows one to determine the rates of passage and the magnitude of erosion, among other factors, indicators for both the state of the Appalachians (equilibrium vs. disequilibrium) and the source of potential disequilibrium (Gallen et al., 2011). The other methodology is aimed at calculating the erosion rates at different places within my study area. The Earth is constantly bombarded by cosmic rays that alter the nuclear structure of atoms they hit. Measuring the concentration of the produced cosmogenic radionuclides provides a way to date different rocks (and sediment) and interpolate erosion rates (Nishiizumi et al., 1991). Spatial comparisons of erosion rates, above and below knick zones, will yield further analysis on the current state of the Appalachians.
Transience in the Appalachians is not a new topic in geologic literature; however, it still is not fully understood. My research aim is to help build on previous research, expanding our understanding and adding fuel to the debate on how the Appalachians have remained so rugged.

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