FEATURES OF ENTRENCHMENT IN CAVES IN THE GREENBRIER KARST, WEST VIRGINIA

Entrenchment by free-surface streams in caves creates undercuts, notches, ledges, cusps, and surfaces of widening. This paper describes the features and shows their use in inferring passage evolution in caves of the Greenbrier karst of West Virginia, USA. Features of entrenchment are occasionally lengthy, extending 10-100 m or more along the length of canyon passages. Usually they are laterally discontinuous but are traceable in contemporaneously formed groups along canyon walls. They slope less than a few degrees downstream along one wall, die out, and then reappear on the same or the opposite wall immediately downflow. Cusps (edges between trench walls and underlying undercut surfaces) cut across bedding, indicating a hydraulic- and solutional origin rather than a lithologic origin. Features of entrenchment extend downstream in canyons to former shafts or chimneys where early ground-water flow changed levels down joints or thrust faults. Features of entrenchment are common within isolated vadose trenches, where flow was along tubes on bed partings and then up joints or faults to higher tubes before descending other joints or faults to lower tubes downstream. Larger undercut surfaces are associated with changes in hydraulic conditions resulting from the introduction of armoring clastic sediments, or with major changes in lithology, as less-soluble impure units are encountered during entrenchment.