Cave

Caves of one sort or another are widely scattered across the planet. Caves can form in limestone, sandstone, loess?, ice, granite?, lava?, marble, and gypsum?. [Limestone cave]?s are the most prevalent, but gypsum and lava caves may be locally very significant. Ice caves occur in and under glaciers. Caves in other types of rocks present more of an engineering hazard than an exploration challenge.

Cave formation in limestone occurs because limestone dissolves under the action of rainwater and groundwater? charged with CO₂ and naturally occurring organic acids. The dissolution process produces a distinctive landform known as karst and characterized by sinkholes?, [sinking streams]?, and caves. Caves can range in size from barely enterable to tropical monsters big enough to fly a light aircraft through.

Discovering caves is firstly a matter of finding limestone (or lava, gypsum, etc.). In the United States, most state geological surveys have [geological map]?s where limestone beds are drawn and can be located in the field. [Topographic map]?s, especially the 1:24000 series, are helpful. After the limestone is located, field work to actually find entrances is necessary.

In the United States, since most land in the eastern U.S. is privately held, permission must be obtained from the landowner to look for caves. In the western U.S., a permit for publicly owned lands may be required.

There many excellent books available, and a local public or university library can help. Of course, a web search can turn up a lot of useful information as well.