SPELEOGENETIC AND SEDIMENTARY DEPOSITION MODELS USED TO AID PALEOFLOOD RECONSTRUCTIONS: COLONIAL ACRES CAVE, SOUTHEASTERN WEST VIRGINIA, USA

The frequencies of extreme floods and droughts may be underestimated in global-scale climate change models because hydrological responses vary regionally. The rapid decay and erosion of surface deposits needed to reconstruct stream behaviors complicates the pursuit of these much-needed studies. Caves are repositories of geomorphic information and can be used to reconstruct paleoflood histories in regions where surface flood deposits are quickly destroyed. However, one must understand how cave sediments are related to a cave’s speleogenesis in order to correctly interpret them. We are reconstructing flood histories in the humid, temperate Appalachian Mountains of West Virginia, USA using Colonial Acres Cave (CAC), which is a branchwork cave containing anastomotic features, suggesting a polygenetic origin. Elliptical and keyhole shaped passages indicate a phreatic origin. The Greenbrier River is the only source of water and sediment to CAC, which only contains water during floods. CAC formed by floodwaters simultaneously enlarging flow paths in sub-horizontal bedding planes in the channel bank. The resulting tubes are essentially extensions of the river during floods and presently contain floodwater-deposited sediments. Their stratigraphies consist of interbedded silts and fine sands containing macerated organic detritus, charcoal, and bat bones. The bat bones definitively show that sediments post-date the cave’s phreatic genesis. At present, CAC records low and intermediate sized floods because most passages are approximately 3 or 4 m above the Greenbrier River. Surprisingly, phreatic sediments are largely absent from the cave, apparently due to vadose scour, and passage morphologies offer the best record of the cave’s phreatic origin. Thus, CAC slackwater sediment and stratigraphy reveals a Late Holocene flood history for the Greenbrier River, which has possible implications for interpreting local hydrological responses to future climate changes.