Once weathered, the particles on the rock are removed through the process of erosion. The most common agents of erosion are water and wind. Running water, in particular, can cut deeply into the Earth's surface and is responsible for the majority of cave formation.
Caves are most commonly formed in soluble rock, such as limestone, gypsum, and salt. These rocks are slowly dissolved by water that contains weak acids, such as those found in rainwater and groundwater. The water seeps into cracks and crevices in the rock and begins to dissolve the minerals that hold the rock together. Over time, the cracks become larger and larger until a cave is formed.
The process of cave formation is ongoing, and caves continue to grow and change over time. As water continues to dissolve the rock, new passages and chambers are created, and the existing passages become wider and higher. Caves can also collapse, creating new entrances or blocking off existing ones.
Caves can be found all over the world, but they are most common in areas with a lot of rainfall and soluble rock. Some of the most famous caves in the world include the Carlsbad Caverns in New Mexico, the Mammoth Cave in Kentucky, and the Reed Flute Cave in China.