KARST

                               Snow-covered Rock Bridge

The middle parts of the Bonne Femme Watershed contain karst landscape, a veritable geologic ‘swiss cheese'. This landscape contains caves, springs, sinkholes, and losing streams. These features make the watershed unique and provide wonderful recreational activities. The groundwater in karst areas is particularly sensitive to pollution since surface water bypasses any filtering of contaminants typically provided by soil.

Karst is formed by the dissolving action of carbonic acid. When rain falls through the atmosphere and percolates through the soil, it absorbs carbon dioxide (CO2) from the air, thereby forming a weak solution of carbonic acid (H2CO3). When this solution reaches bedrock, it flows through cracks in the bedrock. If the bedrock is carbonate (such as limestone), the cracks are gradually enlarged by the dissolving nature of the solution, forming larger and larger conduits for the solution to pass through. Over time, caves and other karst features are formed.

This illustration used with permission of the Missouri Department of Conservation.

   The beautiful cave formation, Soda Straws

KARST DEFINITIONS

Caves: Natural cavities beneath the surface of the earth. In karst regions, caves are created by groundwater dissolving rock.

Losing Streams: Losing streams lose part or all of their flow to the groundwater system by suddenly disappearing underground. The upper Bonne Femme Creek is a losing stream, and provides much of the water flowing through the Devil's Icebox. This inter-watershed transfer of water connects the Bonne Femme and Little Bonne Femme Watersheds.

Natural bridges: Arches that are the remnants of collapsed caves, usually fairly short. Rock Bridge is one such natural bridge.

Sinkholes: Rounded depressions in the landscape. Sinkholes are often collapsed caves and can be quite deep, or they can be shallow holes. Sinkholes collect surface water running off the surrounding land, and the runoff goes directly into the groundwater. The Pierpont Sinkhole Plain (the area surrounding Pierpont) contains numerous sinkholes easily visible from the road. It is called a plain since there are no creeks formed from runoff since it all goes into the sinkholes.

Springs: Natural resurgence, or discharge, of groundwater from rock or soil to the surface.