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. As rain water seeps through soil, it becomes slightly acidic, penetrates cracks and joints, and slowly dissolves porous limestone bedrock. Over time, these cracks and joints enlarge and create a vast underground drainage system. Big Spring carries 173 tons of dissolved dolomite bedrock away in a day, which over one year would equal a new passage about 11 feet wide, 12 feet high, and 1 mile long.