Karst geomorphology and hydrology of the Shenandoah Valley near Harrisonburg, Virginia

GSA Field Guides
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Abstract

The karst of the central Shenandoah Valley has characteristics of both shallow and deep phreatic formation. This field guide focuses on the region around Harrisonburg, Virginia, where a number of these karst features and their associated geologic context can be examined. Ancient, widespread alluvial deposits cover much of the carbonate bedrock on the western side of the valley, where shallow karstification has resulted in classical fluviokarst development. However, in upland exposures of carbonate rock, isolated caves exist atop hills not affected by surface processes other than exposure during denudation. The upland caves contain phreatic deposits of calcite and fine-grained sediments. They lack any evidence of having been invaded by surface streams. Recent geologic mapping and LIDAR (light detection and ranging) elevation data have enabled interpretive association between bedrock structure, igneous intrusions, silicification and brecciation of host carbonate bedrock, and the location of several caves and karst springs. Geochemistry, water quality, and water temperature data support the broad categorization of springs into those affected primarily by shallow near-surface recharge, and those sourced deeper in the karst aquifer. The deep-seated karst formation occurred in the distant past where subvertical fracture and fault zones intersect thrust faults and/or cross-strike faults, enabling upwelling of deep-circulating meteoric groundwater. Most caves formed in such settings have been overprinted by later circulation of shallow groundwater, thus removing evidence of the history of earliest inception; however, several caves do preserve evidence of an earlier formation.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Karst geomorphology and hydrology of the Shenandoah Valley near Harrisonburg, Virginia
Series title GSA Field Guides
DOI 10.1130/2014.0035(06)
Volume 35
Year Published 2014
Language English
Publisher Geological Society of America
Contributing office(s) Eastern Geology and Paleoclimate Science Center
Description 53 p.
First page 161
Last page 213
Country United States
State Virginia
Other Geospatial Shenandoah Valley