Cave

Caves hosted in rocks other than limestone are usually formed by water erosion. For example, rivers running through canyons with steep walls erode the rock at points where the current is strong. Such caves usually have large openings and are not too deep. Caves of this type can be found in the southwestern United States and were at one time inhabited by prehistoric American Indians known as Cliff Dwellers. Sea caves are formed by waves continually crashing against cliffs or steep walls. Often these caves can only be entered at low tide. Ice caves are also formed in glaciers and icebergs by meltwater that drains down crevices in the ice.

Lava caves, which are often several miles long, form when the exterior of a lava flow hardens and cools to form a roof, but lava below the surface flows out, leaving a hollow tube. Wind or aeolian caves usually form in sandstone cliffs as wind-blown sand abrades the cliff face. They are found in desert areas, and occur in a bottle neck shape with the entrance much smaller than the chamber. Talus caves are formed by boulders that have piled up on mountain slopes. The most common, largest, and spectacular caves are solution caves.