Just beneath the Earth's surface, and hidden in complete darkness of caves, are unique rock formations called "speloethems". Many are pristine, beautiful, and mysterious and their forms can take on many colors, shapes, and sizes. Some droop and grow from the ceilings of caves like icicles, while others emerge from the floor like mushrooms. Then there are those that grow downward along the sides of walls and take on a "frozen waterfall" appearance. Unique and delicate life forms, such as cave crickets, crayfish, bats, and eyeless fish are also present in caves. Come join me as we discover the wonders of fragile underground worlds. For better quality viewing, feel free to click on the individual photos for image enhancement. Enjoy!
Albino Cave Crayfish:
Cave Crayfish can live deep within the mouth of caves and never see daylight. And, for this very reason, many cave crayfish are albinos having no pigmented skin. So, how do they live in such habitats? Well, they have tough exoskeletons which support and protect their delicate bodies underneath. Interestingly, if they lose a limb, they simply regrow them as they molt. Albino cave crayfish have no "true eyes", but they do have an excellent sense of smell and touch (antennae) which they use to protect themselves from predators and search for food in the cave surroundings. Cave crayfish have a very low metabolic rate, thus they grow very little from year to year and require less food to survive. In order to survive, cave crayfish must be in high quality water.
Like calcite, aragonite is composed of calcium carbonate. When found in dense, tiny crystals, it is difficult to distinguish between the two because of their internal structure. When the aragonite crystals are large, however, they can be identified by their external structure (habit form). Aragonite crystals are long and needle-like, while calcite tends to be stubby or "dog-tooth-like". Mineral-rich waters with high concentrations of magnesium ions may inhibit the precipitation of calcite, therefore, aragonite is deposited. A common progression from calcite to aragonite may produce a nodular mass of calcite (cave popcorn) tipped by sprays of aragonite needles (left photo).
These beautiful cave formations known as Bacon Drapery are formed by calcium-rich solutions flowing along an overhung ledge of a cave. Such formations are multicolored and generally transparent to translucent. The dark and light bands are products of "waxing" and "waning" supply of organic acids, and the darker reds and oranges are due to various amounts of iron oxide deposits. Erratic paths of previous flow routes cause bacon draperies to form unique ripples and folds. Bacon draperies are very delicate cave formations and can be damaged or broken off by a single touch.
A "bottomless pit" is actually not a bottomless pit. It is basically a natural cave which contains one or more significant vertical shafts rather than being predominantly a conventional horizontal cave passage. Pit caves commonly form in limestone rock as a result of long-term erosion by water. Many spelunkers have descended down into "bottomless pits". Some pits are as deep as 1,000 feet or more, while others, like one of the "bottomless pits" of Mammoth Cave (left photo), measures around 105 feet in depth. This particular pit is located on the "Frozen Niagara" tour at Mammoth Cave National Park (Mammoth Cave, Kentucky).
Boxwork is so named because it resembles a maze of post office boxes. Such formations have intricate networks of fins or plates that protrude in relief from cave walls, ceilings, speleothems, or floors. Boxworks can be composed of any mineral that is more resistant than its surrounding medium, but calcite is the most common deposit. The best exposures of calcite boxworks are found in the caves of the black hills of South Dakota. Most remarkably, are those found in Wind Cave, a national park where blades of crystalline material protrude out from cave walls and ceilings for 24 inches or more.
Rare and fragile type of cave formation, cave balloons are a small, gas-filled pouch made of hydromagnesite. Their origin is not completely known but is likely related to moonmilk. Cave balloons probably occur when solutions under pressure seap into a cave through cracks or out of porous walls of limestone. If they meet moonmilk on their way, the material may expand much like a rubber balloon. They are thought to be short-lived and quickly dry, crack, deflate and change in luster. This is especially true in low-humidity environments. Because of their delicate form and nature, cave balloons are less commonly found than other speleothems. Some are found in Mammoth Cave National Park (Mammoth Cave, Kentucky), Carlsbad Caverns (Carlsbad, New Mexico), and Jewel Cave (Guadalupe Mountains, Texas).
As insect-eaters and plant pollinators, bats may be among the most beneficial animals to people and other living animals. Most bats live deep within caves and rarely come out during the day time. Instead, they wait until nightfall to come out and feed on insects. Brown bats, such as this one, live at Mammoth Cave National Park (Mammoth Cave, Kentucky). Although the bats are smaller in size, Mammoth Cave has twelve different species, including two endangered species. Despite their value to the environment, many species of bats worldwide are needlessly threatened by direct killing, by vandalism, by disturbance to hibernating and maternity colonies, by use of pesticides, and by habitat destruction. Consequently, bat populations in the United States and throughout the world have been declining dramatically.
Cave crickets appear throughout most of the United States. They love moisture and darkness in caves because such areas provide fungus and mold - both of which can feed this particular species of crickets. Those that live most of their lives inside caves generally have lost their pigmented skin. However, unlike the eyeless fish, they have kept their vision in order to travel from one level of the cave to another hunting for food. Unlike most crickets, cave crickets are silent and wingless. They also have very long antennae to feel their way around, and their long back legs make them excellent leapers.
Also known as coralloids, these grape-like cluster forms which are found in Meramec Caverns (Stanton, Missouri) are thought to be some of the rarest cave formations known. This particular kind of formation is said to have formed only when the cave system was underwater. Corallites is a "catch all" name for describing knobby, nodular, botryoidal, or coral-like speleothems. They tend to range in size from tiny beads to globular masses a few feet in diameter. Coralloids include cave popcorn, knobstones, corals, cauliflowers, grapefruits, globularities, and of course, grapes. Most formations can form in open air and underwater.
Cave Lily Pads:
Cave lily pads are created when water droplets containing calcium carbonate (calcite) fall from the ceiling of caves into standing pools of water and create a formation on the floor that resembles a lily pad. These formations occur when a light plate composed of calcium carbonate is held in suspension on the water's surface. When the plates become too heavy, they sink. Other plates successively form one upon the other and through time form a lily pad. Sometimes, small stalagmites grow upward from the center of these pads making them even more intriguing. Although such speleothems are found in various caves throughout the United States, none are more spectacular than those found at Onondaga Cave State Park (Leasburg, Missouri).
Delicate cave pearls, such as these, are stones that form in small pools of water by deposition of calcium carbonate (calcite or aragonite). As mineral-laden water drips down from the ceiling of a cave, it falls upon the small stones turning them about in place. Through long periods of time and continuous mineral deposition, the stones become uniformly coated with calcite or aragonite, thus giving them a pearl-like appearance. As the stones continue to move and tumble about in place, their corners smooth out and the stones themselves become polished. Most cave pearls are white and have a pearly luster which are opaque in nature, but variations will occur.
Cave popcorn is a common name for a bizarre type of speleothem. It can be recognized by its clustered nature and knob-like shape called nodules. These cave formations have concentric layering of microcrystalline calcite. They typically grow from the ceiling but can also grow from the cave floor. Cave popcorn forms by precipitation where water seeping through the limestone walls or splashing them deposits calcium carbonate. They may also form by evaporation, thus giving them a chalky appearance like popcorn. The cave nodules are relatively small ranging from .20 to .78 inches and often form with other speleothems, such as aragonite needles.
Cave rafts are relatively thin-like structures that form on the surface of cave pools. They form when drip water, containing mineral deposits, hits the surface of a cave pool and spreads out to form a thin crust. Older pool basins can have mineral deposits several feet thick. Most cave rafts are delicate and made of calcite or aragonite. The thin rafts float on the surface of the cave pools due to the surface tension before eventually sinking when they become too heavy or when the pool is disturbed. Cave rafts that are found on the floor of some dry areas of a cave indicate that the passages were once flooded. This photo shows uniquely-shaped cave rafts floating on the surface of a cave pool in Lechuguilla Cave, New Mexico.
Cave Soda Straws:
Speleothems form in caverns where water seeps through the cracks up above. When the water reaches the air in the cave, some of the carbon dioxide in the solution escapes from the drop and calcium carbonate precipitates (forms). Deposition then occurs as a ring around the edge of the water droplet. As drop after drop follows, each leaves a very small trace of calcite behind, and a hollow limestone tube can be made. Those that have a hollow tube are called soda straws while those that plug up and deposition continues are called stalactites. Both grow from the ceiling of caves.
Stalactites and stalagmites often grow in pairs and sometimes will grow together to form columns. Columns include among the ranks of the tallest free-standing speleothems in the world. They are less common because they take a very long time for the formations to meet and grow together. Columns can continue to grow even after they form becoming larger and larger in diameter. In fact, some columns are large enough that stalactites will grow from their sides. Like columns, it takes many years for speleothems to grow; however, due to chemical changes in the carbonic acid, they do not always grow at the same speed.
Perhaps the most unusual form of fish found in caves are those cave-adapted species known generally as "eyeless fish". Through time, they have adapted to living in darkness in low energy environments by ceasing to grow eye structures and pigmented skin. Eyeless fish can be found in an underground river called "Echo River" at Mammoth Cave National Park (Mammoth Cave, Kentucky). The "Echo River Tour", one of the cave's most famous attractions, use to take visitors on a boat ride along the underground river. But due to conservation purposes designed to protect the eyeless fish and other unique life forms found in the cave, the tour was discontinued. Cave crickets, crayfish, and beetles are also found living in the darkness of Mammoth Cave.
Flowstones are perhaps the most common forms of cave deposits. They are composed of sheet-like deposits of calcium carbonate (calcite) formed when water flows down the walls or along the floors of caves. Flowstones are usually white or translucent but may be stained various colors by minerals dissolved in the water. These unique cave formations often resemble cascading waterfalls, thus giving them the informal name of "frozen waterfalls". Though flowstones are among the largest of the speleothems, they can still be damaged by a single touch. The oil from human fingers causes the water to avoid the area, and as a result, they dry out and cease to grow.
Frostwork is generally a spiny speleothem resembling a cactus or thistle plant. It is the needle-like habit of aragonite that gives it a frost-like appearance. However, frostwork can also be composed of calcite, opal, gypsum, ice, and other minerals. It is usually white but can also be other colors including blue. Frostwork is a common form of of cave formations and can be found on stalactites, cave walls, ceilings, ledges, and floors. By all means, their displays can be dazingly, fragile, and intricate forms of speleothems, but because of their beauty and easy access, they are unfortunately often vandalized or destroyed by carelessness.
Made from calcium sulfate (gypsum) or halite (common salt), these speleothems have crystal petals radiating out from a central point. The "flower petals" are fibrous or prismatic crystals that grow in a parallel orientation. Their unique crystals grow from the ceiling from the base - not the tip as do stalactites. Due to changes in flow rate, the "flower petals" tend to curve. Gypsum flowers form in relatively dry, non-dripping conditions. Flower gypsum growth in crevices, may cause portions of the cave walls to breakdown. Such formations are found abundantly on the "Grand Avenue" tour at Mammoth Cave National Park (Mammoth Cave, Kentucky).
Helictites are strangely shaped stalactites called "soda straws" made of calcium carbonate (calcite) that grow sideways as well as downward. Such fascinating speleothems resembled twisted tree branches, but on a smaller scale. They seem to defy gravity as they bend and turn in all directions, and some can grow into antler-like forms. The twisted shapes of Helictites are due to factors, such as calcium carbonate impurities and air currents within the cave causing changes in flow direction. Good displays of Helictites are rare, but beautiful ones can be found in Carlsbad Caverns National Park (Carlsbad, New Mexico).
Moonmilk is a white, creamy substance found in caves where it forms very fine crystals that vary in calcium carbonate composition. These fine-grained particles become suspended in water, which gives the deposits an appearance of milk. Moonmilk is generally soft and pasty when wet but crumbly and powdery when dry. When wet, moonmilk feels and looks like cream cheese, but when dry, it feels and looks like talcum powder. Moonmilk is probably related to "cave balloons". Throughout the ages, moonmilk has been used for medicinal purposes, such as an aid to stop bleeding, reduce fever, diarrhea, and stomach acid.
Pool fingers are finger-like calcite formations that appear in cave pools and former cave pools usually under shelfstone. Many of them resemble "soda straws" but are more lumpy, have no internal canal, and sometimes form loops. Pool fingers are very rare, but when found, they are always pendent beneath some kind of overhang. Most hang from the "shelfstone" but others hang from the cave wall. The origin of these unique formations are unknown; however, they are suspected to be composed of calcified organic material.
Pool spar is composed of calcite or gypsum that has crystallized under water in a cave. This happens when the water is stable and remains for a very long time. Even if water is not currently present, you can see where the water level was based on where the formation is located. Pool spar has distinctive large, clear crystals that often grow at the end of a stalactite. The calcite and gypsum crystals may be transparent, translucent, or opaque. Like this one, they may also grow in the form of needles radiating out from a central point. Just like the aragonite sprays, a progression from calcite to aragonite may be observed.
A stalactite is a type of speleothem that hangs from the ceiling of caves. They most commonly occur in limestone caves. Stalactites form through the deposition of calcium carbonate and other minerals, which is precipitated from mineral-rich water solutions. An average growth rate is about 0.0051 inches a year. However, some grow quicker because they are formed by faster flowing water rich in calcium carbonate. These can grow at 0.12 inches per year. Unlike soda straws that have hollow tubes, stalactites eventually plug up by debris. As a result, water begins flowing over the outside depositing more calcite and creating the more familiar cone-shaped stalactites.
Stalagmites are a type of speleothem that rises from the floor of a cave due to the accumulation of material deposited on the floor from the continuous dripping of water from the ceiling. They form through the deposition of calcium carbonate and other minerals which are precipitated from mineral-rich waters. Stalagmites come in various colors, shapes and sizes. They all start out small and continue to grow upward as long as there is a steady supply of mineral-rich flowing water. The largest known cave stalagmite is about 204 feet tall and is located in Cuba.