How is a cave?

Answer 1

Caves can form in a variety of ways, but most caves are dissolutional and are initially formed by chemical weathering of surface rock, usually limestone, by carbonic acid contained in rainwater. As chemical weathering continues, mechanical weathering joins in the fun to further attack and widen joints and fissures in what is usually soluble sedimentary rock, like limestone.

Some other types of caves are formed by percolating sulfuric acid, flowing lava, flowing water in glaciers, wave action, and particle abrasion.