HYDROLOGY AND GEOMORPHOLOGY OF A HIGHLY KARSTED UPLAND: THE GREENBRIER VALLEY AND LITTLE LEVELS, WEST VIRGINIA

The Greenbrier Valley of West Virginia, on the eastern edge of the Appalachian Plateaus physiographic province, is a broad limestone terrane that is heavily karstified. Low-order surface drainage is nearly absent, and the groundwater system is a mix of confined and unconfined aquifers, fractures, and conduits (caves). Six of the 25 longest caves in the U.S. are found in the region, including Organ Cave (65 km). Regional base level is the Greenbrier River, which is incised 150 m below the karst surface.

Present-day recharge is dispersed across the karst surface, with limited sinking streams at the margin of the karst. Cave development is controlled mainly by bedding planes, although faults and joints are locally important. Development is localized at the contact between the Hillsdale Limestone and underlying Maccrady Shale. Subsurface drainage is dendritic, with waters ultimately resurging at the Greenbrier River. Low-order subsurface tributaries tend to be dip-oriented, while the higher order conduits are strike oriented. Many portions of the conduit system in upper positions are currently dry. Sediments found in the dry conduits range from clay to cobble size, and include occasional Mastodon fossils. Clast angularity and poor sorting document periodic(?) extreme flow conditions. In Organ, Buckeye Creek and Windy Mouth caves magnetically reversed sediments indicate an age of at least 0.78 Ma for the oldest parts of these drainage systems. Correlation of near-river magnetically reversed sediments provides a minimum incision rate of 0.04 m/ka for the Greenbrier River.

The landscape is evolving through the following processes. The karst plain is widening through retreat of clastic-capped mountains on the valley margins. The karst plain is lowering through denudation of the limestone floor. The Greenbrier River is cutting through the plain, at a fairly slow rate. The cave systems all appear to post-date glacial rearrangement of the Ohio River basin, and there is no obvious evidence for knickpoint propagation in the caves examined thus far. It is likely that evolution of this surface has been episodic, and that climatic changes have had a strong influence on the rate of each of the processes mentioned.