Karst is a special type of landscape formed by the dissolution of soluble rocks, including limestone and dolomite. A karst topography is characterized by rolling hills, deep hollows, springs, caves, sinkholes, and tunnels. Rain water seeping through soil becomes slightly acidic, penetrates cracks and joints, and slowly dissolves porous limestone bedrock. Through time, the cracks and joints enlarge, creating a vast underground drainage system. Big Spring carries 173 tons of dissolved dolomite bedrock away in a day. Over one year, this would equate to a new passage about 11 feet wide, 12 feet high, and 1 mile in length.