HOW CAVES ARE FORMED
This page is designed to give you a basic understanding on how caves are formed. The main source of all cave development is water. Some shelter caves may be developed by wind, but for all intents and purposes we will talk about caves that are developed in the limestone layers of the earth. Limestone is a rock that is highly soluble in water which is enriched with carbonic acid. The water comes from rainfall and when it enters the soil it mixes with plant material where it picks up carbon dioxide. The mixture of carbon dioxide and water forms a carbonic acid. The carbonic acid enriched water finds its way into the water table. This can be referred to as ground water. The ground water finds its way into tiny pores and cracks in the limestone layer and slowly begins to dissolve the limestone. As time goes on the pockets and cracks enlarge to form small chambers in the rock. There are occasions that the water table can create a hydrostatic pressure which will erode the limestone rock away quicker. As time goes on the erosion process creates larger crevices and passages for the water to flow in. More ground water is able to enter the passages and erode away the limestone even more quickly. The passage grows in size with each rainfall, but this is a slow process. No one is able to predict how long it takes a cave to form. Some caves are formed faster than others and this all depends on the geological layout of the area. Eventually in geologic time passages are formed which are large enough to walk in. All water that enters a cave must eventually leave the cave at some point due to the underlying geology of the earth and these areas are called springs or resurgences. The areas where the water enters the cave are called insurgences.
Passageways come in all shapes and sizes. Some are tight and narrow, while others can be very low and wide. There are passages that are large enough to drive large trucks through and there are chambers big enough to put an entire NFL football stadium into. Each cave is unique to itself with a mixture of different shapes and sizes of passage. The length of a cave system is totally determined by the surrounding geology. There are different names for different types of cave passages. A phreatic passage is formed when the passage is completely filled with water and under pressure during the early development of the cave. Paleotrunk passages are large passages that were eroded by water but the stream no longer follows them. Canyon passages are passages formed by downward-cutting, moving water and the streams are present in these passages during normal or wet conditions. These passages are generally taller than they are wide. Infeeder stream passages are smaller stream passages that feed the larger main drainage of the cave. A siphon is an area of the cave where the ceiling is very low and water usually fills the passage to the ceiling. Sometimes siphons can be traversed during very dry weather. A near siphon is a place where the ceiling and the water are very close to each other. These can usually be traversed during normal conditions but cannot be traversed during high water. A sump is a downstream terminus to a passage where the water and ceiling meet. There are very rare conditions which will allow a caver to pass a sump but these are far and few between. Almost in all cases a sump must be passed using diving equipment. Cave diving is not the same as scuba diving because it takes special training and certification to become a cave diver. Even with extreme caution and skills cave diving is a very dangerous event. Fatalities have occurred even with the most experienced of cave divers. Pits are holes or openings in the cave floor which may lead to lower levels in the cave, and require training in descending and ascending a rope with the proper equipment. Ascending or descending a rope in a cave environment is different than its counterparts on the surface. Cave conditions are often wet, muddy and cold. The environment alone is not as friendly to ropes and equipment so therefore it requires different techniques and gear than one would use on the surface.
Formations in a cave come in all different shapes, sizes and colors. Generally speaking the formations seen in a cave are made out of calcite which is a precipitate of Calcium carbonate. The added colors are due to mineral impurities mixed in with the calcite. Calcium carbonate is highly soluble in the carbonic acid found in ground water. The ground water becomes saturated with calcium carbonate on its journey through the limestone. The air in a cave is chemically the same as air outside the cave with the exception that it is very low in carbon dioxide. The ground water entering the cave is very high in carbon dioxide and calcium carbonate. Therefore the ground water entering the cave is out of equilibrium with the cave environment and there is a transfer of carbon dioxide to the cave atmosphere causing calcite to precipitate out. This is how formations are formed. A water droplet that hangs from the ceiling of the cave will leave a small deposit of calcite before it is forced to fall to the floor of the cave. The repetition of this act forms what is called a stalactite on the ceiling of the cave and a stalagmite on the floor of the cave. If the process is allowed to continue long enough the two will join to form a column. There are numerous names for different types of formations such as: draperies, curtains, bacon, soda straws, shields and rimstone just to name a few. Needless to say the process is the same whether it is accomplished from a drip from the ceiling or water running down the wall of a passage. Formations are delicate works of nature which can take thousands of years to form. There are other minerals and formations seen in caves such as Fluorite, Dogtooth Spar, Helectites, Aragonite and Gypsum but these types of formations are much rarer and even more delicate.
There is also life or fauna found in caves. These come in all shapes and sizes, from a microscopic organism to larger species like bats and salamanders. Crayfish can be found living in the streams of caves, as well as different species of fish. Generally most species that inhabit a cave have pigment and eyes but there are some species that have no eyes or color due to a long genetic evolution. These are the exception rather than the rule. Crickets and small beetles also inhabit cave environments. The list of fauna is too large to describe them all but I have given you a few examples of what to expect.
Remember every cave has an owner. This does not necessarily mean that they own the cave but they do own the property which the cave entrance lies on. Entering a cave without the permission of the landowner is trespassing. Caves are also protected by law whether it be state or federal, and there are fines imposed on those who would destroy any part of the cave environment. The motto of a good caver is to take only pictures, leave only footprints (and as few of those as possible) and kill nothing but time. I hope that my little chapter on how caves are formed was informative. Also remember that I am no expert on the formation of caves and if anyone sees any material presented on this page as inaccurate, please email me at caver18@attbi.com and I will be happy to correct it.
Your Caving Friend,
Ed McCarthy
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