A cave is a natural opening in the earth’s surface large enough for a human to enter. Caves are found all over the world and occur in many different types of rock, from limestone to granite. Some caves are very small, while others, such as Carlsbad Caverns in New Mexico, USA, or the Cueva de las Manos in Argentina, are enormous.
Caves can be formed by a number of geological processes. The most common type of cave is one that has been carved out by water flowing over rocks. This process is known as erosion and can take place either above ground or below ground. Cave systems can also be formed when lava flows cool and harden around an existing rock structure; this is how the lava tubes on Hawaii were created. Less commonly, caves can form as a result of tectonic activity (movement of the Earth’s plates) or even meteorite impacts!
The vast majority of caves are found underground, but there are some that are completely open to the air. These ‘sea caves’ are carved into cliffs by wave action and can be found along coastlines all over the world. The biggest sea cave in the world is Kealakekua Bay Cave on Hawaii; it measures an impressive 150m (490ft) wide and 30m (100ft) high!
Caves provide homes for many different animals, including bats, rodents, snakes, spiders, and insects. Some species have adapted to life entirely within caves; these ‘troglobites’ include fish that lack eyesight and albino crabs that have no pigment in their shells. Many other animals use caves only occasionally; bats roost inside during the day and fly out at night to hunt for food, while bears may use them as dens to hibernate through winter months. Humans also use caves for shelter; some examples of this include prehistoric paintings found in European ‘caveman’ dwellings and more recent uses such as storing wine or cheese underground where temperature and humidity levels remain constant throughout the year