How are caves formed?

Caves are among the most mysterious places in nature: dark, silent chambers and winding passages hidden beneath the surface of the Earth. Some are small hollows, while others are vast networks of tunnels stretching for kilometers. It can be hard to imagine how such large empty spaces came to exist deep inside solid rock. The most common type of cave forms through a slow and patient process driven by water.

The story of most caves begins with a particular kind of rock, most often limestone. Limestone has a special property: it can be slowly dissolved by acidic water. This is the key to cave formation. Where there are thick layers of limestone, the conditions are right for caves to develop. Other similar rocks can also form caves in the same way, but limestone is by far the most common, which is why this kind of cave is often called a limestone cave.

The water that carves caves is not strong acid. It starts as ordinary rainwater. As rain falls through the air and then soaks down through the soil, it picks up carbon dioxide gas. This makes the water slightly acidic, forming a weak natural acid. This mild acidity is gentle, but it is enough. As this slightly acidic water seeps down into the limestone, it begins to chemically dissolve the rock, very slowly carrying tiny amounts of it away.

The acidic water flows along natural cracks, joints, and gaps in the limestone. Wherever it travels, it dissolves a little more rock, gradually widening these cracks. Over thousands and even millions of years, the steady flow of water enlarges narrow cracks into channels, channels into passages, and passages into great chambers. Underground streams may form, carving the cave further. The result, after an immense span of time, is the hollow underground world of a cave. The same dripping, mineral-rich water often goes on to build the icicle-like stone formations seen inside many caves.

This article was written using information from Wikipedia.