In karst areas, three kinds of water movement contribute to erosion (and by extension cave formation): 1) surface streams, 2) underground drainage flows, and 3) groundwater. Within the formation of a karst system, there are three solution processes at work: 1) dissociation: anhydirte, halite, and gypsum dissociate in the presence of water. As an example, gypsum dissolves until the concentration reaches 2500 mg/L. At this point precipitation starts. 2) Solution: Rainwater absorbs atmospheric gases as it passes through the atmosphere, so that water and a small amount of carbon dioxide combine to become a weak acid. In this form rainwater becomes an effective solvent for rainwater. 3) Sulphidic weathering: some cave formation occurs because of the presence of sulphidic bacteria which produce sulphuric acid, which dissolves limestone. This picture is from within a karst system known as Cadomin Caves.
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