All About Caves
A cave is a hollow space underground large enough for a person to enter. It can be formed by various means. Caves can take thousands of years to form. They can be formed from gypsum, dolomite, marble or limestone. These are rocks which can dissolve quite easily.
Erosion causes most caves. The acid in rainwater seeps through cracks over time. The cracks get bigger and become caves. Caves can also be caused by chemical actions, tectonic and volcanic action, microorganisms and pressure. An exception is the hollow lava tubes found in the Hawaiian Islands. The formation of caves depends on hydrology (the water system nearby), topography (the landform which exists at any given place) and geology (the type of rock at the site). Caves may have small or large openings and may connect to many others in an underground maze.
The study of caves is called speleology. People who love exploring caves are sometimes called spelunkers. People like to go spelunking, caving or potholing. Speleogenesis is the word for the formation of caves.
Caves formed in something other than limestone usually are made from water erosion. Fast flowing rivers erode the rock where the current is strong. These caves are not too deep. Caves like this are found in the southwestern United States and were lived in by early people called Cliff Dwellers. Sea caves can sometimes only be entered at low tide. They have been formed by the waves crashing against the rocky cliffs. Ice caves can be formed in glaciers.
Blowing sand can erode cliffs and form caves. These are called aeolian caves. These caves are found in desert areas. The opening is small, but the inside is much larger. Lava caves are formed when the hardened lava leaves molten lava below it which flows out and creates caves. When large boulders stack up on mountains, caves can be forms. These are called talus caves.
Solution caves are the biggest caves. They are formed by chemical weathering when water seeps through a crack. The ground formation is called karst. It is like the floor of the cave. A solution cave can be identified by sinkholes, circular depressions, natural bridges and disappearing streams. Sometimes the entrance to such a cave may be hard to find.
The karst is formed when water drains through the soil and mixes with carbon dioxide from the air. Carbonic acid is created. This acid works to dissolve the calcium carbonate in the rock. Water keeps on flowing and makes the caves larger. Sometimes the caves connect to form passageways underground. Heavy rain can erode the rock even more.
Some solution caves are formed when hydrogen sulfide gas is released from the earth's crust. When this gas touches water, it becomes sulfuric acid. This weathers or wears away the rock in a chemical way.
The inside of a cave is always dark and maintains pretty much the same temperature all year round. Limestone caves have a humidity of one hundred percent. Some caves have interesting forms called speleotherms in them. Calcite is the most common mineral of a speleotherm. When a drop of water on the ceiling of a cave hangs down, calcite comes out of the solution. It runs down the wall and is deposited there over and over forming a curtain. A buildup of hanging drops of water from the ceiling is called stalactites. When drops reach the ground and build up, stalagmites are formed.
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