River Styx Spring (Mammoth Cave Ridge, Kentucky, USA)
In the Mammoth Cave area, groundwater moving via conduit flow emerges along many springs adjacent to the Green River, such as Turnhole Spring, Pike Spring, Echo River Spring, and River Styx Spring.
The River Styx Spring is located due west of & downhill from Mammoth Cave's historic entrance. The rocks at River Styx Spring are part of the upper St. Louis Limestone (Meramecian Stage, Middle Mississippian) and include the interval normally containing the Lost River Chert Bed. The chert bed is mostly absent here due to a lateral facies change. River Styx Spring itself is an overflow exit conduit for the Echo River Spring.
Under fair weather conditions, all of the springs near local base level are at relatively low flow and water moves away from them & toward the Green River. During and after storms, the springs, the short streams draining them, and even the subterranean rivers in the cave system often experience flooding and water flows AWAY from the Green River. The lowest set of cave passages is Level F - water levels can rise significantly and even completely fill level F passages during Green River flood events. Occasionally, even portions of level E can be backflooded (for example, River Hall, which can be viewed during the Historic Tour).