Geologic Aspects of Karst in the Appalachians

Orndorff R.C.¹, Epstein J.B. ¹, Weary D.J. ¹, and Harlow G.E. ²

¹U.S. Geological Survey, National Center, MS926A, Reston, VA 20192

²U.S. Geological Survey, 1730 East Parham Road, Richmond, VA  23228

Solution of relatively soluble rocks, such as limestone, dolomite, and gypsum, produces a terrain termed karst that is characterized by a variety of features, including caves, springs, sinking streams, and sinkholes. Ground-water movement may be very rapid through enlarged conduits, making shallow aquifers in karst extremely vulnerable to contamination from both point and non-point sources. Residual soil, which may plug sinkholes, can collapse and cause considerable destruction to homes, buildings, roads, railroads, impoundments, etc. Many millions of dollars in damage annually occurs in the U.S. from such collapse. Thus, understanding geologic controls on karst development is of national significance. This understanding can be accomplished by preparing maps that outline karst areas, by researching the processes that localize karst development, and by presenting this information in a manner useful for hazard mitigation.

A new project entitled Karst and Subsidence Hazards has been proposed to the National Cooperative Geologic Mapping Program. The main goal of this karst project is to produce geologic maps at a variety of scales, ranging from 1:24,000 to 1:7,500,000 that will form the foundation for developing new techniques and methods to better understand geologic controls on karst systems. Derivative maps and research papers will characterize the relationship of geologic structure and stratigraphy to karst development. A variety of tasks will be addressed:  (1) ground-water contamination, (2) sinkhole formation, (3) development of new techniques for analyzing karst through remote sensing and geophysics, (4) identifying regional karst issues by producing a karst map of the Appalachians, and (5) addressing national issues through development of a new National Atlas karst map. New techniques will be used to address karst-subsidence hazards and ground-water contamination issues at local, regional, and national levels. These data will be presented to aid researchers and land-use managers in hazard mitigation and environmental protection.

One specific task involves detailed geologic mapping in the northern Shenandoah Valley of Virginia and West Virginia in the area of a major karst aquifer. A hydrogeologic framework will be determined through analysis of conduits and fractures and their relationship to springs, sinkholes, caves, and losing streams determined through a karst inventory. The geologic information will then be compared with water data to assess geologic controls on ground-water movement, storage, and quality. For example, water quality and quantity data can be correlated to stratigraphy and lithologies in order to investigate any relationships between hydrology and geology. A karst inventory will be produced by several methods of remote sensing that will include maps of sinkholes and surface basins that drain to sinkholes. This karst inventory will be compiled on geologic maps to evaluate geologic controls on karst development such as comparison to structures and stratigraphy.

Karstic rocks underlie about one-quarter of the land area of the U.S. In order to educate government managers and the public to the distribution of karst at the national and regional scales, a digital map of karst will be produced for the National Atlas at a scale of 1:7,500,000. Federal agencies (National Park Service, Bureau of Land Management, National Forest Service) have expressed an interest in combining a national karst map with one showing Federal lands. This map will be useful in determining which Federal facilities may have karst resources within their borders, especially those facilities that are unaware of it.

A detailed map of the Appalachian highlands will be the beginning of the national map. The effects of stratigraphic and structural control on karst development in this classic fold-fault belt of highly fractured rock will be researched and areas of importance delineated for further biologic, hydrologic, and geologic research. Karst features that may be included on the map are: exposed soluble rocks, including limestone, dolomite, and evaporites; intrastratal karst; karstic rocks beneath surficial overburden; percentage area covered by karst; and features analogous to karst, so-called “pseudokarst”.

Orndorff R.C., Epstein J.B., Weary D.J., and Harlow G.E., Geologic Aspects of Karst in the Appalachians

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