Did You Know:
- The longest free-hanging stalactite in the world at 23 feet hangs in a cave in Ireland.
- The longest cave system in the world is Mammoth Cave, which has over 350 miles of mapped caves, and more which is unexplored. The second longest is a gypsum cave in the Ukraine, which is 113 miles long. The third longest is Jewel Cave in South Dakota, at a length of 106 miles.
- The tallest stalagmite resides in a cave in France and is 98 feet tall!
The most caves in the U.S.
- The temperature of a deep cave is equal to the average temperature at the local surface.
- About 60 percent of the Ozarks region is underlain by soluble rock.
Formation Process of Solution Caves
Caves are distributed widely across the globe. So far, about 17,000 caves have been discovered in just the U. S., and many more have yet to be discovered. Formed mostly in environments where limestone is present, caves offer some of the most beautiful sights in the world with their unique structures. Parts of caves can be very small and impassible to humans, or they can be as large as the Big Room in Carlsbad Caverns, NM, which has an area of 14 football fields!
Geologic Processes and Products
Caves form from a variety of geologic processes depending on the environmental factors of the area. The most important and influential process involved in the production of caves is the power that water possesses by means of erosion and weathering. Described below are caves formed from lava, the sea, the carving of ice, and the solution of limestone in areas of karst. Excepting lava tubes, water is the key factor in the formation of these caves.
----Lava Tube Caves
Lava tube caves (like the one above) originate during a volcanic event, in which lava pours out from the opening in the earth's crust and begins to flow downhill. The very hot lava begins to cool down and harden on the outside, forming an insulating outer shell through which the hot lava can keep flowing at a fast rate. The lava continues to flow and harden at the surface until the eruption stops and the remaining lava is drained, leaving behind a tube of hardened lava. Below are a few diagrams that exemplify this occurence.
Sea caves are formed when weak zones of sea cliffs are attacked by wave action. These weak zones may consist of a fault, fracture, types of rock differing in weakness (such as an intrusion), or thinly bedded sandstone layers. The erosional ability of the waves are enhanced by the sediment which they carry, which grinds repeatedly on the cliff walls with every wave. Sea caves begin as small cracks within the weak zones, and gradually increase in size as they are eroded by the waves and suspended sediment. Sea caves are concentrated in places all over the world, including the Pacific coast of the U.S. and the Greek Isles.
----Ice (glacier) Caves
Ice caves originate from flowing water through large ice masses, carving out hollows. During the summer season, the water that melts from the glacier finds the weakest parts of the glacier, mostly cracks or faults, and the cracks get wider and deeper as the river of meltwater runs on. Exposed cracks in the ice can be covered by more layers of ice and snow, creating what is called a snow bridge. The glaciers move very slowly, only a few inches per year, but this movement is enough to cause the collapse of many ice caves. Many new caves are formed by the newly melted water every summer season. The beautiful eerie blue color of ice caves is created by light which tries to penetrate the ice.
Solution caves are formed in limestone and other rocks of similar composition through weathering and erosion by water. Precipitation from the earth's atmosphere seeps into pores and cracks of soil and rock and gravitates down to the saturated zone (zone saturated with water), the surface of which is known as the water table. The rainwater absorbs and reacts with carbon dioxide from the atmosphere to form a weak carbonic acid solution. This solution slowly dissolves carbonate rocks and forms cavities and passages. The cavities and passageways are formed where the maximum amount of continuous water flow occurs, right below the water table. Once the water table has lowered, leaving the caves in the aerated zone, the deposition of calcite occurs, creating different beautiful "decorations" called speleothems.
Speleothems are generally defined as cave deposits from water, also known as dripstone and flowstone. The two speleothems most commonly referred to are stalactites and stalagmites. Stalactites are the formations on the ceilings of caves that look like icicles, created when the carbon dioxide in the water seeping through cracks escapes into the air and the calcite precipitates. Stalagmites are speleothems which stick up from the floor of a cave. They are formed when water drops from cracks in the ceiling and splatters on the floor, and the included calcite then precipitates. Sometimes growing stalactites and stalagmites join and form a column, reaching from the floor to the ceiling. Helictites are speleothems with centers through which water flows by capillary action, which is why they can grow in any direction, appearing to defy gravity. In China, it has been found that some stalagmites are composed of microlayers, that when studied under a microscope, can be used for cross-dating and are important for dating events in the history of caves and interpreting ancient cave climates.
Solution caves are most often found in areas known as karst, named after the Kras Plateau in Slovenia, which is formerly part of Yugoslavia. Places that have been formed by the dissolution of limestone by groundwater show karst topography. Such places are found all over the world. First the groundwater seeps into the soil and rock material and develops caves and caverns through solution below the water table. Sinkholes begin to form when cracks and fractures in rocks are widened, and the overlying soil material "sinks" down into those hollows, creating depressions of various depths. Many sinkholes can be found in Kentucky, southern Indiana, and northern Florida. Over time, the caves and caverns collapse as gravity becomes too much for their structure. This, along with the coalescence (joining) of sinkholes, results in larger, flat areas of depression. In places like China, most of the limestone has been removed, and only the tower karst are left standing, jutting up from the ground. The tops of these tower karst once were basically the land surface long ago.
It has been found that caves can also form from the dissolution of rock by a weak sulfuric acid solution. The hydrogen sulfide that mixes with oxygen from water to make sulfuric acid comes up through the earth. The two parts are mixed by bacteria that are called Snot-tites because of the gooey appearance of the secretions that they produce. These Snot-tites produce energy through chemosynthesis, and their excrement which contains sulfuric acid helps carve out caves.
Caves and the processes that form them have been operating for a very long time, obviously, creating underground and surficial features that are a wonder. They serve as directories that channel water to different areas of the saturated zone. Caves are also host to myriads of fascinating and exotic species that have adapted to the cave environment, like species of fish without eyes. Human civilization is greatly influenced by caves. Humans have explored caves for ages, intrigued by the mystery found within. Caves have sheltered many kinds of people and exhibit many ancient paintings created by them, telling of history. The Maya of Central America thought that caves were passages to the underworld and that if they performed rituals in the caves, their ancestors would notice them more easily. Native Americans viewed caves as sacred places. People have used caves for food storage, weapons storage, moonshine storage, and mining of profitable material. Even more interestingly, during World War II caves were used as dance halls, and the people that used to own Mammoth Cave in Kentucky used to hold concerts and marriage ceremonies in there! Nowadays, caving (or spelunking) is a popular (yet dangerous) form of sport. I have a recently developed yet great affinity for caves. It is amazing to me how dark and creepy it can get in those places. Another thing that is incredible is how caves can cause such a feeling of helplessness and being caught.
Bloom, Arthur L. Geomorphology: A Systematic Analysis of Late Cenozoic Landforms. Upper Saddle River: Prentice Hall, 1998.
Herberman, Ethan. "Cave of Goo!" Current Science. 84 (1998): 8-9.
Matty, Jane M. "Caves and Sinkholes." Rocks & Minerals 70 (1995): 296.
Ming, Tan; Xiaoguang, Qin. "Bioptical microcycles of laminated speleothems from China and their chronological significance." Chinese Science Bulletin 44 (1999): 1604-1607.
Tarbuck, Edward J. and Frederick K. Lutgens. Earth: An Introduction to Physical Geology. Upper Saddle River: Prentice Hall, 2002.
Author: Gabriel Fuson
Creation/revision date: 3 May 2002
Other websites from the Earlham Geology 211 Class:
is part of a Geology 211 class project on Processes in Physical Geology.
Copyright ©-2001 Earlham College. Revised 25 February 2002. Send corrections or comments to firstname.lastname@example.org