The most common process by which limestone caves form involves carbonic acid—or weakly acidic groundwater—as the primary agent. When carbonic acid contacts limestone, it dissolves minerals in the rock. If enough water to saturate the rock is present over a long time period, cavities and entire underground cave networks can form. Recently, a radical new theory has been proposed that identifies another cave-forming agent: sulfuric acid. This video segment adapted from NOVA identifies the mysterious source of the sulfuric acid, which, unlike carbonic acid, does not readily form in nature.
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