October 13, 2009
Enigmatic waterfalls like the one above occur at a number of locations on the Mississippian Period (c. 350 mya) Greenbrier limestone of eastern West Virginia. They’re unusual in that they lack a surface stream either above them or below them. Limestone is sparingly soluble in slightly acidified groundwater and in time, open solution channels may develop. If such channels are large enough, they’re referred to as caves.
In West Virginia, the Taggard shales separate the Greenbrier formation into an upper limestone unit and a lower limestone unit. Since the shales are insoluble, no solution channels can form in them and they serve as a barrier to the movement of groundwater. Because groundwater cannot flow through the shale, it flows around it at the shale's surface outcrop. The waterfalls occur where water reaches the surface from solution channels at the base of the upper limestone. Water issues from the ground as a spring, cascades over the vertical surface outcrop of the Taggard formation, and immediately sinks back into the ground as it re-enters solution channels in the lower limestone units.
The Greenbrier limestone contains the majority of West Virginia's 3,000 or so known caves. Many of these caves have entrances just above or just below the outcrop of the Taggard shales. Landscape features such as caves, sinkholes and large springs are associated with karst terrains. The term "karst" refers to a landscape type in which solution of the underlying bedrock is the dominant geological process. Photo taken 6 miles (10 km) west of Elkins, West Virginia in the Monongahela National Forest.