EVALUATION OF 2-DIMENSIONAL KARST POROSITY USING A COUNTYWIDE CAVE MAP DATABASE

The likelihood of intersecting vadose or phreatic caves during drilling is of interest from both exploration and environmental standpoints. If one is seeking resources such as petroleum or groundwater, a cave may be an exploration target. But if a feature is intersected unexpectedly, severe environmental and/or engineering problems may result. This chance of hitting a given cave can be definitively known if the exact position and dimensions of such features are available, but there are many unmapped/unknown caves. Existing cave maps have the potential to be used to evaluate overall probability of intersecting karst voids. For this study a catalog of published cave maps of Monroe County, West Virginia, USA was used. This area covers 1,227 km squared, and is in the deformed Appalachian Plateau with caves developed in Paleozoic rocks. Maps were available for 79 out of the 207 listed caves, and 76 of the maps were suitable for analysis. Optical scan and pixel counting were used to determine 2-d porosity, which was defined as the ratio of area of cave passages to the area of the minimum sized bounding rectangle. Cave lengths ranged from 17 to 16,500 m, with an average length of 610 m. Short caves are much more common than longer ones. Length of cave corresponds strongly to cave area. 2-d porosity ranged from 0.7% to 70%, with an average of 17%. There is a weak correlation between increasing cave length and decreasing 2-d porosity. In general, longer caves have lower overall porosity. Other researchers using smaller datasets have found weak opposite correlation. There is no dependence on rock unit. Very short caves can give unrealistically high porosities. Karst porosity occurs throughout the carbonate regions of the county, but caves are not known from all locations. Limitations on data suitability can come from: unknown/unmapped caves, incomplete mapping, variations in map quality (caves were mapped by volunteers having varying experience levels), and secrecy. As exploration and mapping continue, a more robust data set will be available. There is a wealth of data available in the form of published cave maps from all over the world, which could be employed to extend this analysis to other areas.