Document Type

Thesis

Abstract

Recent mapping of a broad 5 kilometer (km) knickzone located ~130km upstream of the Richmond Fall Zone on the James River, central Virginia Piedmont, indicates the mechanism of incision and knickzone creation is largely controlled by the underlying bedrock. This current hypothesis was determined through detailed analysis of reconstructed terrace profiles, field mapping and surveying, and past '"Be cosmogenic radionuclide dating. Nearly all current data supports the hypothesis that the knickzone has been largely stationary during the last | Ma, though it is possible that the river has experienced multiple migratory knickzones during this time. This research project works to further these earlier efforts by focusing on how certain lithologic and structural characteristics maintain a dominant control on knickzone placement and orientation. Precise surveying of the river surface throughout the knickzone is used to construct detailed longitudinal profiles that are correlated with lithologic and structural data. Evidence is also drawn from the construction of a 1:12,000 scale bedrock and surficial geologic map of the study area, analysis of longitudinal and cross valley profiles of the main channel and tributaries (created from 1: 24,000 scale topographic maps) in combination with analysis of aerial photographs of the study area, channel flow direction in tributaries and site specific field observations. Future plans involve constraining rates of incision within the knickzone using '"Be cosmogenic radionuclide dating techniques to date terrace deposits. Terraces several kilometers up and down stream of the knickzone have already been dated. A detailed interpretation of the James River knickzone will be helpful in determining the extent of landscape disequilibrium in the piedmont, and further hypothesizing the mechanism for this disequilibrium.

Date Awarded

2008

Department

Geology

Advisor 1

Gregory S. Hancock

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