CONTROLS ON PASSAGE FORMATION IN POMPEY'S CAVE, ULSTER CO., NEW YORK STATE

Pompey's Cave, the longest cave in Ulster Co., New York, is developed within the limestone of the Glasco Member of the Upper Silurian Rondout Formation, bounded above and below by the dolomitic Rosendale and Whiteport members, respectively. Under normal flow conditions, the cave takes the entire flow of Kripplebush Creek, sinking where the upper contact of the Glaco Member crosses the stream channel, and seemingly resurges where the member again crosses the stream channel due to folding of the strata. A dry streambed developed in the overlying Whiteport Member overlies the cave, carrying water only during higher flow rates. At a gross scale, the Pompey's Cave can be split into a downstream and upstream section, split by short passage that constricts water flow between the sections. During high flow rates the upstream portion of the cave floods completely, with water flowing overland down the normally dry streambed and sinking into the lower section of the cave at entrances developed within the streambed. During very high flow rates the lower section of the cave also floods entirely, with water flowing both underground and overland over the entire length of the cave passage.

Revised detailed mapping of the cave indicates multiple controls on passage formation. The main trunk passage of the cave in the downstream section is primarily oriented along the axis of an anticline trending roughly northwest-southeast with few side passages, indicating development along structurally-controlled fractures. The upstream section of the cave also consists of a main trunk section, but with much greater development of smaller side passages with multiple interconnections, indicating initial development associated with similar downstream structure, but with superimposed floodwater maze development as well, probably associated with more frequent flooding events due to the mid-cave restriction. Midstream entrances seem to be developed where parasitic anticlinal folds along the main anticline allow for water to seep into cracks through the overlying dolomite and sink into the underlying limestone, ultimately resulting in roof collapse entrances. Ongoing projects at Pompey's Cave include detailed mapping of small-scale stratigraphic units and structure within the cave along with continued flow measurements at various flow regimes.