KARST HYDROGEOLOGY OF THE GREAT SMOKY MOUNTAINS

The geology of Great Smoky Mountains National Park (GRSM) in Tennessee and North Carolina is dominated by siliciclastics and metamorphic strata. However, in the western portion of the Park a series of carbonate fensters (windows) expose the lower Ordovician section of the Knox Group, a series of dolomite and limestone units which are partially marbleized as a result of contact metamorphism from the Great Smoky Fault. The fensters create opportunities for allogenic recharge to occur at points along the contact of the surrounding insoluble strata with the underlying carbonates. The combination of chemically aggressive recharge and vertical relief has resulted in the formation of deep caves, many of which have active streams and water resources. Though the karst is limited in extent and the number of caves is fairly small, the significance of the resources is substantial, with several of the caves in the area over 150 m in depth and at least two major bat hibernacula. Cades Cove, a large carbonate fenster, is one of the National Park Service’s most-visited sites. In 2017, the U.S. Geological Survey began a study to better understand the hydrologic behavior of these karst systems through hydrologic and geochemical monitoring, dye tracing, and seepage runs. Stage and water quality instrumentation was placed in the main stream of Bull Cave and in a sump pool in White Oak Blowhole, at 173 m and 70 m below land surface respectively. Following setup of the cave sites, dye injections were conducted to determine discharge points for four of the deep cave systems on Rich Mountain and Turkeypen Ridge. Results show these systems to have an extremely rapid travel time with tracers detected from caves to springs in less than 24 hours for each of the systems. To characterize streamflow, a real-time surface water gage was installed in May, 2017 along Abrams Creek, the main stream in Cades Cove. Analysis of seepage run data along the tributaries and main stem of Abrams Creek will quantify losses and gains as streams flow off of the insoluble strata and sink at the carbonate contact. The karst of GRSM provides an opportunity to study a unique landscape characterized by complex geology, high stream gradients, and deep caves. The investigation is being conducted in cooperation with Tennessee Wildlife Resources Agency, GRSM, and Tallassee Fund.