My Science School

Spelunking is the recreational sport of exploring caves, but no one really calls it spelunking anymore. The acceptable term -- and the one we'll use here -- is caving.

Caving, like scuba diving or rock climbing, is as adventurous as you want it to be. There are family-friendly caves you can stroll through on a paved path. And there are others that require hundreds of feet of face-in-the-dirt crawling and rappelling down bottomless shafts.

There are thousands of caves in the United States, and more than 100 are open to the public for guided tours and expeditions [source: National Caves Association]. More than 200 U.S. caving clubs offer organized excursions to remote caves, teach advanced caving skills and participate in cave conservation.

Humans have been drawn to caves since ancient times. Modern archeologists have found evidence that ancient people viewed caves as sacred locations in which to carry out important religious rites. In prehistoric times, caves were attractive dwellings that offered stable interior temperatures and protection from harsh weather and other humans. In more recent history, caves have served as hiding places for stashed treasure, ideal environments for aging cheese and wine, and excellent natural labs for scientific discovery.

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Carlsbad Caverns National Park, area of the Chihuahuan Desert in southeastern New Mexico, U.S., near the base of the Guadalupe Mountains (a segment of the Sacramento Mountains). It was established in 1923 as a national monument, designated a national park in 1930, and proclaimed a UNESCO World Heritage site in 1995. Beneath the park, which has a surface area of 73 square miles (189 square km), are 83 individual caves, including Carlsbad Cavern, the park’s namesake. The park also includes Rattlesnake Springs, a small enclave about 5 miles (8 km) to the southeast.

About 250 million years ago, a shallow sea ringed by a vast, horseshoe-shaped limestone reef covered the area. This formation, called Capitan Reef, is found in southeastern New Mexico and western Texas and includes Guadalupe Mountains National Park, just southwest of Carlsbad Caverns National Park. After the sea evaporated, the constant dripping of acidic groundwater carved out the massive underground chambers, converted limestone to gypsum, and formed enormous stalactites, stalagmites, and other cave deposits ranging from the delicate to the bizarre.

Carlsbad Cavern has a labyrinth of underground chambers, including one of the largest ever discovered. The total length of the rooms and passages is still unknown, but the explored part of the main cavern is more than 30 miles (48 km) long, of which 3 miles (5 km) are open to visitors. Of the three major levels, the deepest is 1,027 feet (313 metres) belowground. Visitors can walk or take an elevator to the 755-foot (230-metre) level and explore the Big Room, which measures about 2,000 feet (610 metres) long and 1,100 feet (335 metres) wide at its greatest extents and has a ceiling that arches 255 feet (78 metres) above the floor. Found within are the Giant Dome, a stalagmite 62 feet (19 metres) tall; the Twin Domes, only slightly smaller, superbly proportioned and delicately fluted; and the so-called Bottomless Pit, which is some 700 feet (210 metres) deep. During the summer a colony of about one million Mexican free-tailed bats inhabits a part of the caverns known as Bat Cave; each evening at sunset they swarm out of the cave’s entrance to feed in the surrounding area.

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The study of caves is called speleology. A scientist who studies them is a speleologist. Speleology is both a niche area of geoscience and a broad area of study that looks at many aspects of caves. There is much we can learn from these curious geological formations, from how they formed to which zoological species inhabit them, to their geological profile, examining how stalagmites and stalactites form, their internal hydrology (the profile and processes of water bodies within caves). They will also be interested in caves as habitats for paleontological and anthropological remains.

Caves are often a microcosm of niche ecology, therefore those with a professional interest in the biological sciences - zoology, botany, mycology, entomology might be drawn to speleology too in examining the native plants and animal species that grow and thrive within a cave system. In recent years, researchers have found plants that can grow in very low light levels. Understanding these plants may shed light on a variety of interrelated issues such as plant genetics.

Caves are also important sources of mineral deposits. Speleologists might work to mine these resources or examine how they might have come to form there. Speleologists might also work as cartographers, developing maps for caves used for recreational or tourist use - devise the safest route through a cave, or come up with ways to ensure they are safe. They work mostly in caves but will spend their time between offices and labs and the cave systems that they study.

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Blind cave fish compensate for their lack of sight by having a more sensitive lateral line system which detects vibrations or changes in pressure in the water. The lateral line is a specialized sensory organ found in fish. It is a canal system running just under the skin along each side of the fish’s body.

The blind cave fish has skin covered with a layer of scales arranged in head-to-tail pattern, similar to shingles on a roof. These scales play a protective role for the fish and reduce drag when swimming. Fish also secrete a layer of mucus that covers their body, further reducing drag in the water. The mucus also helps prevent infection by serving as a barrier to microorganisms and also makes the fish slippery and difficult for predators to catch.

Blind cave fish compensate for their lack of sight by having a more sensitive lateral line system which detects vibrations or changes in pressure in the water. The lateral line is a specialized sensory organ found in fish. It is a canal system running just under the skin along each side of the fish’s body. This canal is lined with special receptors that are quite sensitive to vibrations and water currents and thus it is an “extended sense of touch” allowing the blind cave fish to detect obstacles at a distance. Using this heightened sense helps blind cave fish find food and avoid bumping into obstacles.

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When a stalactite touches a stalagmite it forms a column. Usually, stalactites and stalagmites in caves are formed by calcite, less frequently by aragonite, and rarely by gypsum. Fifty-four other cave minerals are known to form rare stalactites.

Sometimes calcite stalactites or stalagmites are overgrown by aragonite crystals. This is due to precipitation of calcite that raises the ratio of magnesium to calcium in the solution enough that aragonite becomes stable.

Rarely, elongated single crystals or twins of calcite are vertically oriented and look like stalactites, but in fact are not stalactites because they are not formed by dripping or flowing water and don't have hollow channels inside. These elongated crystals are formed from water films on their surface.

The internal structure of stalactites and stalagmites across their growth axis usually consists of concentric rings around the hollow channel. These rings contain different amounts of clay and other inclusions, and reflect drier and wetter periods. Clay rings reflect hiatuses of the growth of the sample. Stalagmites may be formed for periods ranging from a few hundreds years up to one million years. Stalactites and stalagmites in caves have such great variety of shapes, forms, and color that each of them is unique in appearance. At the same time, their growth rates are so slow that once broken, they cannot recover during a human life span of time. Thus, stalactites and stalagmites are considered natural heritage objects and are protected by law in most countries, and their collection, mining, and selling is prohibited.

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On this day in 1986, a mining tradition dating back to 1911 ended: the use of canaries in coal mines to detect carbon monoxide and other toxic gases before they hurt humans. New plans from the government declared that the “electronic nose,” a detector with a digital reading, would replace the birds, according to the BBC.  

Although ending the use of the birds to detect deadly gas was more humane, miners’ feelings were mixed. “They are so ingrained in the culture, miners report whistling to the birds and coaxing them as they worked, treating them as pets,” the BBC said.

At the time, it was the latest of many changes in the British mining industry, which was a source of great strife in the country through the 1980s. Pit ponies, the other animal that went underground with human miners to haul coal, were also phased out by automation. The last of them retired in 1999, wrote Clare Garner for The Independent.  

The idea of using canaries is credited to John Scott Haldane, known to some as “the father of oxygen therapy.” His research on carbon monoxide led him to recommend using the birds, writes Esther Inglis-Arkell for Gizmodo. He suggested using a sentinel species: an animal more sensitive to the colorless, odorless carbon monoxide and other poisonous gases than humans. If the animal became ill or died, that would give miners a warning to evacuate.

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Stalagmites have thicker proportions and grow up on the bottom of a cavern from the same drip-water source, the mineral from which is deposited after the water droplet falls across the open space in the rock. Not every stalactite has a complementary stalagmite, and many of the latter may have no stalactite above them. Where the paired relation exists, however, continual elongation of one or both may eventually result in a junction and the formation of a column.

When dripping water falls down on the floor of the cave it form stalagmites, which grow up vertically from the cave floor. Any changes in the direction of the growth axis of the stalagmite are suggestive of folding of the floor of the cave during the growth of the stalagmite. If a stalagmite is small, flat and round, it is called button stalagmite. Stalagmites resembling piled-up plates with broken borders are called pile-of-plates stalagmites. Rare varieties of stalagmites are mushroom stalagmites (partly composed of mud and having a mushroom shape), mud stalagmites (formed by mud) and lily pad stalagmites (resembling a lily pad on the surface of a pond). A calcite crust (shelfstone) grows around a stalagmite if it is flooded by a cave pool and forms a candlestick.

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Stalactites hanging from the ceilings of caverns commonly exhibit a central tube or the trace of a former tube whose diameter is that of a drop of water hanging by surface tension. A drop on the tip of a growing stalactite leaves a deposit only around its rim. Downward growth of the rim makes the tube. The simplest stalactite form, therefore, is a thin-walled stone straw, and these fragile forms may reach lengths of 0.5 m (20 inches) or more where air currents have not seriously disturbed the growth. The more common form is a downward-tapering cone and is simply a thickening of the straw type by mineral deposition from a film of water descending the exterior of the pendant.

There are many other types of mineral formations found in caves. Some deposits are named based on their appearances, such as a showerhead, which is a hollow cone-shaped formation, or a conulite, which is a “splash cup” that forms when water dripping rapidly through the cave ceiling flings aside loose particles on the cave floor. And the list goes on.

Some caves are fully submerged, underwater. Studying underwater caves, such as those in Bermuda, can give us clues about how climate and sea level have changed over time. This knowledge can, in turn, help us better understand and respond to current climate and sea level fluctuations.

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A veil of darkness cloaks the natural beauty of caves. Some are found in cliffs at the edge of the coastline, chipped away by the relentless pounding of waves. Others form where a lava tube's outer surface cools and hardens and the inside of the molten rock drains away. Caves even form in glaciers where meltwater carves tunnels at the beginning of its journey to the sea.

But most caves form in karst, a type of landscape made of limestone, dolomite, and gypsum rocks that slowly dissolve in the presence of water with a slightly acidic tinge. Rain mixes with carbon dioxide in the atmosphere as it falls to the ground and then picks up more of the gas as it seeps into the soil. The combination is a weak acidic solution that dissolves calcite, the main mineral of karst rocks.

The acidic water percolates down into the Earth through cracks and fractures and creates a network of passages like an underground plumbing system. The passages widen as more water seeps down, allowing even more water to flow through them. Eventually, some of the passages become large enough to earn the distinction of "cave". Most of these solutional caves require more than 100,000 years to widen large enough to hold a human.

The water courses down through the Earth until it reaches the zone where the rocks are completely saturated with water. Here, masses of water continually slosh to and fro, explaining why many caverns lay nearly horizontal.

Credit : National Geographic 

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