Cave
From Wikinfo
[[de:H�hle]]
A cave is an underground void that is large enough to be examined in some way by man and which was formed by nature.
This is not the only definition of a cave but is the most commonly used one. It does not include all the ways the term cave is used in the common language. In particular, it excludes all man-made "caves", which are better called subterranea. Also, mines are not caves.
Caves are formed naturally by geologic processes. There are hundreds of ways that caves can be formed. They typically involve a combination of chemical processes, tectonic forces and atmospheric influences. First there are caves formed at the same time as the surrounding rock, like lava tubes and blister caves. These are called primary caves. Then there are secondary caves, which are formed inside the rock by processes which removes material.
Those processes are solution and erosion. Erosion is a mechanical form of weathering which is caused by running water, a cave river which works on its bed deepening it or waves (on coasts). This process is not depending very much on the type of rock.
Solutional caves 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.
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 underground drainage.
Limestone solution is the single most important process forming caves and the origin of probably 80% of all caves on Earth. The main reason for the overwhelming number of karst caves is the fact that much of the surface is built of limestone, but also the slowness of the solution process. If it was faster, the life span 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. Although calcite and aragonite speleothems are most common, there are virtually hundreds of different speleothems known. The world's most spectacularly decorated cave is generally regarded to be Lechuguilla Cave (New Mexico, USA).
Caves can also form through the abrasive action of rivers, the wind, or the sea. 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 rather small. There are also some special cases; glacier 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.
Lava tubes are formed through volcanic activity. They are the most common primary caves. Lava flows downhill and the surface cools down and becomes hard. The lava now flows inside its crust, until the eruption ends. The liquid lava inside the crust flows out and leaves a hollow tube. 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.
Caves can reach considerable dimensions. Of the cave systems that have been discovered so far, the most extensive is Mammoth Cave (Kentucky, USA; 560km of passage). The deepest cave changes rather often, as every year new cave branches are discovered all over the world. The deepest caves of the last years are Voronya Cave (Abkhazia, Georgia) and Lamprechtsofen (Austria). The current (2003) number one is Gouffre Mirolda (Haute Savoie, France) with a height difference of 1,733m between the highest and lowest entrances. The largest individual cave room found is the Gua Niah or known as Sarawak Chamber (Borneo, Malaysia; area 700m by 300m, height 70m) - big enough to accommodate 40 Boeing 747s or to fly a light aircraft through.
Caving and spelunking are a popular activities in several countries. But there are numerous restrictions which should be considered. 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. Other countries have laws which generally prohibit the visit of caves, other allow it only in the company of local cavers. Some caves are closed completely for certain reasons. But even in accessible caves many laws apply in order to protect them.
Despite the legal matters, caves are generally very fragile and any visit harms the cave. Cavers developed their own ethics and even the casual cave visitor should obey the most important ones: do not destroy anything, do not leave anything, do not take away anything.
Caves are also an archaeological treasure house as primitive people used caves as their shelter and sometimes burial place. Items placed in caves are protected from climate and scavanging animals. One example is the Great Cave of Niah, which is one of the largest limestone caves in the world as well as an archaeological treasure house. It was here that archaeologists discovered the evidence of Man�s existence dating back 40,000 years. That is another reason why caves should be protected from casual intrussion.
See also
External links
- NSS Geo2 Committee on Long and Deep Caves A website with numerous pages on cave world records, e.g. longest and deepest caves. Compiled by Bob Gulden.
- Classification of Caves Very detailed list of cave types with links to further information
- The Virtual Cave A site with exceptional photography by Dave Bunnell, the editor of the NSS News. Make a virtual caving trip!
- About gua Niah
In addition to the usual meaning of the term there are three locations in the United States with this name. They are in Stevens County, Kansas, Lincoln County, Missouri and Pendleton County, West Virginia.
Caves is also the name of a commune in the Aude [[d�partement]], in France
References
- Adapted from the Wikipedia article, "Cave" http://en.wikipedia.org/wiki/Cave, used under the GNU Free Documentation License
