Document Type

Thesis

Abstract

The widespread distribution of features generally associated with periglacial processes throughout the Central and Southern Appalachians has led to hypotheses that Pleistocene periglacial processes are the dominant mechanism for Appalachian landscape evolution. Summit form, boulder stream characteristics, and the occurrence of cyroplanation terraces have specifically been used as evidence for the extreme nature of these processes. Periglacial erosion rates have been estimated at 100-300 m My". Because these are approximately ten times greater than modern fluvial erosion rates, several authors have suggested that the form of many Appalachian summits is controlled by periglacial processes and that the uplands are evolving towards a form most efficient for transporting periglacially derived colluvium. Long term average erosion rates were derived by measuring the concentrations of in situ produced cosmogenic '°Be from a variety of bare bedrock surfaces in Dolly Sods, WV. The mean rate of summit lowering is 6.4 m My", although individual measurements vary between 2.5 and 11.0m My”. A comparison to nearby long term fluvial erosion rates shows that relief, at least in the Dolly Sods area, is increasing at a rate of 20-45 m My”. Peak elevations may also be increasing following isostatic compensation. A numerical model was developed to constrain maximum rates of periglacial erosion given certain erosion scenarios and the long term averages we observed. The results of our simulations suggest that, given a 10,000 yr duration of periglacial climate, rates of periglacial erosion are no more than 10-50 m My”. Similar rates of long term fluvial incision suggest that periglacial erosion processes are not extreme. Boulder deposits, summit form, and the distribution of cryoplanation terraces were analyzed in an effort to determine the extent to which periglacial processes are responsible for their development. Measurements of orientation and a variety of field evidence suggest that much of the summit colluvium is simply weathered regolith and that most side slope boulder streams have been deposited by debris flows. Although periglacial processes may be involved in some of these deposits, it seems the vast majority of colluvium in the Dolly Sods area has no periglacial origin. The form of broad summit flats is strongly controlled by the extent and structural geometry of the underlying conglomerate unit. Proposed cryoplanation terrace treads occur only in siltstone/shale units while their risers occur in more resistant sandstone/conglomerate units. The strong lithologic and structural control of summit form and cryoplanation terraces is inconsistent with a strict periglacial interpretation. We conclude from a wide variety of evidence that periglacial erosion is not extreme in the Dolly Sods uplands. Theories of Appalachian landscape evolution may need to be adjusted to include a more steady erosion history that is invariable with climate.

Date Awarded

2002

Department

Geology

Advisor 1

Gregory S. Hancock

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