Sinkholes are depressions formed by the collapse of the surface layer, often due to what dissolution process?

• A. Wind erosion of soft rock
• B. Volcanic activity
• C. Dissolution of limestone
• D. Rapid rainfall erosion causing surface collapse

Answer: (C)

Sinkholes arise when water that is slightly acidic dissolves soluble rock like limestone, slowly creating underground voids. Over time, these voids weaken the support for the overlying surface, and the ground collapses, forming a sinkhole. The dissolving action is driven by carbonic acid formed when rainwater mixes with carbon dioxide in the air and soil, which readily dissolves calcium carbonate in limestone, carving out caverns and conduits. This karst process explains why regions with abundant limestone commonly develop sinkholes. Other options don’t involve the dissolution of rock to create hidden cavities: wind erosion affects exposed rock but doesn’t produce large subsurface voids; volcanic activity forms craters through eruption rather than dissolution of rock; rapid rainfall erosion creates surface runoff and channels rather than the underground void collapse that defines sinkholes.