Anyone who has traveled through Greenbrier County West Virginia has witnessed a unique land feature known as Karst topography. The terrain in the Greenbrier valley rolls along porous limestone that in some places is several hundred feet thick. Throughout time this limestone has dissolved and eroded, leaving behind multiple sinkholes, deep fissures and other land depressions. The combination of these geological features in the presence of groundwater leaves behind underground caves and streams. West Virginia contains eight sinking creeks and their tributaries, all under Greenbrier and Pocahontas Counties. In this paper, one of the underground steams will be explored and discussed, but first, a close examination of topography and Geology in this area.
Karst topography develops in many areas throughout the United States where relatively pure limestone is located both above and directly beneath the surface. "Groundwater is directly responsible for the majority of the features formed either by dissolution of the surrounding rock or by the deposition of minerals originally carried in solution." The most important characteristic of all Karst areas, is that they are all made up of under lying bed of highly soluble rocks. The most common minerals in Karst topography are calcite, CaCO , and dolomite, CaMg(CO ) . These minerals exist as rocks, more commonly referred to as limestones, and dolomites. Both of these rocks are found in the geology of Greenbrier County. However, a grayish limestone with black spots and streaks is most dominant. This rock can be easily seen above surface in formations up to twelve feet in height and even larger. Underground and combined with water, this limestone takes on a pinkish, white color.
Karst develops by the dissolution of limestone by moving groundwater. "The volume of groundwater depends on the porosity and permeability of the aquifer. The development of Karst also requires large quantities of water to dissolve the rock and form underground passages."
Sinkholes and protruding portions of limestone are the most common
feature of the Greenbrier Valley. These depressions range from
several feet to sinkholes nearly 500 feet in diameter. "The
most common type of sinkhole is the solution sinkhole, it forms
by the progressive dissolution of the limestone in the immediate
vicinity of a set of intersecting fractures called joints."
Solution Sinkhole (after Renton)
Another type of sinkhole happens when the roof of a cave collapses. This is called a collapse sinkhole, the existing limestone becomes to weak to support the weight of the land and a destructive collapse occurs. Collapse sinkholes are common in underground streams.
To understand these sunken creeks and streams, you must analyze
the subsurface drainage movement of water in Karst areas. "Some
geologists believe that Karst areas have a classic water table,
meaning that all space below the water table is filled with water...
In this interpretation, the passage ways constitute a confined
aquifer system that is totally independent of any water table."
One of the most famous underground streams in West Virginia is Milligan Creek. It is located near Lewisburg in Greenbrier County. The short drive west of Lewisburg provides a scenic view of this unusual topography. To either side of the road, you see rolling green hills scattered with sinkholes and depressions. Jutting blades of limestone can also be seen throughout this landscape. You begin to imagine the number of caves and subterranean passages below the surface. Turning left, you travel 2-3 miles parallel with Milligan Creek, a cow pasture stream that is characteristic of a high order stream, a sinuous meandering pattern that flows slowly between its banks.
To reach the entrance of this cave, you must park and walk along the stream. At the point at which the stream sinks into the land, there are small boulders and limestone rocks. With a flashlight, headgear, and change of clothes, you can slowly descend 10-12 feet into this cave. This is more wisely attempted in the summer when the water is running low, and there is less pressure forcing you inside. The passage is a small rippled limestone formation that resembles a waterslide. Ten feet down, you can crawl on your knees and observe a small room. Water is dripping from pores in the stone as well as flowing as a creek. This small room is as far as one can go, but on your stomach and looking through the small entrance way, you can barely trace the stream with your eyes and ears and imagine the pattern the water has carved through the years.
This stream provides a pristine environment for many animals living
in and about the water. Milligan Creek is well known for its
self-sustaining brown trout population. These trout are not affected
by the drop and sinking action of the water, they routinely travel
through and survive in the underground stream. This part of the
state and country is a unique area that can provide spectacular
views to the unknown. The lack of surface water in this area
is easily replaced by the mystery of the Karst topography and
the thought that streams and creeks are flowing underground.