Caves are underground openings and passageways that have been formed by a number of geologic processes, including chemical weathering, wind and water erosion, tectonic movements, glacier melting, fracture of rocks and digging, among others. Caves formed by dissolution of rock are the most common types of caves. Rock is dissolved by the chemical reaction with acid water that filters through the cracks and openings in the ground. Over time, cracks expend and become caves systems. The most abundant caves are formed in limestone. Limestone dissolves under the action of carbonic acid (H2CO3) contained in rain or underground water.
A cave or cavern is a natural cavity or opening within the Earth’s crust. Caves form naturally by geological processes, such as weathering of rock, but they can also formed by man, such as digging into the ground for minerals. Caves may form due to a number of geological processes. Some caves form through chemical and water erosion. Others form due to tectonic plate movement and some others form by the precipitation of minerals. Another type of cave formation is by dissolution of limestone from sulfuric acid. In this type of formation, hydrogen sulfide coming from underground oil deposits mixes with water, forming sulfuric acid and dissolving limestone.
Most caves form in limestone, which is one of the most abundant types of sedimentary rock. Limestone is composed of the minerals calcite and aragonite. The main source of calcite in limestone is made from fragments of marine organisms such as corals. Limestone is highly soluble under acidic solutions. The solubility of limestone leads to the creation of a variety of land forms. Land forms from the dissolution of limestone include caves, cenotes, pot holes and gorges, among others. The solubility of limestone prevents the formation of ponds and streams over limestone bedrocks. The process by which limestone caves form is by dissolution.
Rain and limestone caves
Caves that form from the dissolution of limestone are the most common type of caves, although, caves can also form by dissolution in other type of rocks, including marble, chalk, salt and dolomite. The largest and most abundant caves are those that form in limestone. Limestone dissolves when in contact with rainwater and underground water that contain carbonic acid (H2CO3) and other organic acids. Calcite, the main component of limestone, dissolves in the presence of carbonic acid to produce calcium and bicarbonate. Acidic water flowing through the limestone rock removes mineral ions and creates a cavity or opening.
Limestone caves often include calcium carbonate formations through slow precipitation of calcite. These formations include stalactites, stalagmites, curtains, soda straws, flowstones and columns, which in conjunction are called speleothems. Most speleothems are made of minerals, including calcite, aragonite and dolomite, although some others are made of silicates and evaporites. Stalactites form when water droplets precipitate out of the cave’s racks and joints and release CO2, forming a ring of calcite at the place where a drop of mineral water falls inside the cave, forming a tube-like structure known as a stalactite. Additional drops may form a mound-shaped structure called as a stalagmite.
Throughout history, ancient civilizations have utilized caves for a number of human practices, including the burial of death people, shelter and to place personal items for protection. Many archeological treasures, including paintings, carvings and jewels, have been discovered while exploring caves. There’s evidence that some caves have been inhabited by humans in dates that go as far back as 50,000 years. According to dwb.unl.edu, chemical erosion by acidic rain washes away stone and sand and over thousands or even millions of years a cave is formed.