QUANTITATIVE MEASUREMENT OF CAVE PASSAGE CROSS SECTIONS, SCOTT HOLLOW CAVE, WEST VIRGINIA

Conduits in carbonate aquifers form by the flux of water along initial rock discontinuities. The capability of the conduit to transmit water, solutes, and sediments is directly related to the cross-sectional area of the conduit. In order to evaluate if standard cave survey techniques accurately measure conduit cross-sectional dimensions, we conducted eighteen high-accuracy surveys in Scott Hollow Cave (Monroe County, WV). A variety of passage shapes and sizes were chosen for this evaluation. Initially, following traditional cave surveying techniques, estimations of the width and height of the cave passage were made at each station. A tripod mounted laser device was then used to measure distance to 16 radially distributed points at each station. These data were used to calculate the area of each cross-section for comparison with the estimations. Areas of the passages ranged from 2 to 180 meters-squared. An average absolute error of 65% was found. Width and height were usually overestimated. This shows that a substantial amount of error is produced when using the traditional cave surveying method. Each cross-section was then represented using different numbers of points and geometric approximations. Depending on cave passage type and size, the number of points and geometric shape required to give an accurate representation of the cross-sectional dimensions varied. Sixteen points, however, was usually sufficient. Passage types that are troublesome to measure and represent are those having significant convexity, such as “keyhole” types. In these instances, placement of the survey instrument becomes critical to a reasonable representation. Loose material, such as breakdown and finer sediments, can also be problematic. The method developed could be further applied in calculating the accurate volumes of entire cave systems. This has ramifications for understanding the storage and flow of fluids such as water, sediments, oil, and gas.