Cave: Encyclopedia II - Cave - Types and formation

Cave - Types and formation

Caves are formed by geologic processes. These may involve a combination of chemical processes, tectonic forces and atmospheric influences.

Cave - Primary caves

Some caves are formed at the same time as the surrounding rock. These are called primary caves.

• Lava tubes are formed through volcanic activity. They are the most common primary caves. Lava flows downhill and the surface cools and solidifies. The lava now flows under this crust, until the eruption ends. If the liquid lava inside the crust flows out, a hollow tube remains.

The most important lava tubes are found on Hawaii (Big Island). Kazumura Cave near Hilo is the longest and deepest lava tube of the world and also the eighth longest cave of the United States.

• Blister caves are also formed through volcanic activity.

Cave - Secondary caves

Secondary caves are formed inside the rock after the rock itself has formed by processes which removes material such as solution and erosion.

• Sea caves are very common at all coasts of the world, but as they are restricted to the zone where waves work on the rocks of the coast they are generally rather small.

• Ice caves occur in and under glaciers, formed by melting. They are also influenced by the very slow flow of the ice which tends to close the caves again.

• Solutional caves may form anywhere with rock which is soluble, and are most prevalent in limestone, but can also form in other material, including chalk, dolomite, marble, loess, ice, granite, salt, lava, sandstone, and gypsum. The most common process of cave formation is karstification, which is the solution of rocks by rain water.
  • Fracture caves are formed when layers of more soluble minerals such as gypsum dissolve out from between layers of less soluble rock. These rocks fracture and collapse in blocks.
• Talus caves are the openings between rocks that have fallen down into a pile, often at the bases of cliffs.

Cave formation in limestone occurs because limestone dissolves under the action of rainwater and groundwater charged with CO₂ (carbonic acid) and naturally occurring organic acids. The dissolution process produces a distinctive landform known as karst and characterized by sinkholes, sinking streams, and underground drainage.

Limestone solution is an important process in cave formation and the origin of the great majority of all caves on Earth. The reasons for this abundance are the facts that limestone is so common and the slowness of the solution process. If it were faster, the lifespan of limestone caves would be much shorter and their number much lower.

Limestone caves are often adorned with calcium carbonate formations produced through slow precipitation, including the most common and well-known stalactites and stalagmites. These secondary mineral deposits in caves are called speleothems. The world's most spectacularly decorated cave is generally regarded to be Lechuguilla Cave (New Mexico, USA).

Lechuguilla and nearby Carlsbad Caverns are now believed to be examples of another type of solutional cave. They were formed by acid rising from below, where reservoirs of oil give off sulfurous fumes, rather than by acidic water percolating from the surface.

Adapted from the Wikipedia article "Types and formation", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki