"What am I looking at?" It might take your eyes a moment to adjust, but these crazed pale columns and teeth of stone are all part a totally natural formation. This composite feature is known as the Doll's Theater, and it can be found in the "Big Room" of Carlsbad Caverns, New Mexico. Caves, cracks, tubes and tunnels of all kinds can be found all throughout the Earth's crust, and these below-ground lairs offer some of the weirdest and most awe-inspiring sights created by the meandering machinations of the geological world. Read on to see more!
Image Credit: NPS Photo by Peter Jones
A Park Service official introduces a tour group to the entrance of Mammoth Cave, Kentucky. No doubt there comes a warning to stick close to the tour and to remain on the well-marked trails -- and this is for a good reason. Mammoth Cave is the longest known underground cavern in the entire world, with more than 390 miles (628 kilometers) of charted passageways. Ergo, not the best place to take a wrong turn.
Image Credit: U.S. National Park Service
This is the same eerie entrance, but shown from the inside, under a glaze of winter ice. And for those of you who are about to break out your terminology and classify these dangling spikes as stalactites -- simmer down. They're just icicles. Patience.
Image Credit: U.S. National Park Service
It's perfectly common for diurnal, surface-dwelling mammals like us to fear danger in the dark. But can you imagine what it's like for organisms on the other side of that coin -- the ones that dwell in black abysses -- who might fear light as much as we fear the dark? Mammoth Cave is known for hosting a fascinating underworld ecosystem of dark-loving life forms. The eyeless fish shown above has evolved a perfect set of adaptations for the sunless cavern where it lives -- not needing eyes, it has ceded them to sightless disks, and living without pigment, it is nearly as pale and shiny as a prism caught in the light.
Image Credit: U.S. National Park Service
Here's a creeper for you. This pure white crayfish has been living in the dark for so many generations that it, like the eyeless fish shown previously, has learned to live without a photon's worth of help. Small organisms that have adapted to live entirely within cave systems are known as troglobites. This, for example, is a troglobite crayfish -- Orconectes pellucidus -- which is one of the primary predators of the Mammoth Cave ecosystem.
Image Credit: U.S. National Park Service
Kentucky's Mammoth Cave remains the longest known cave system in the world, and even though it was discovered by ancient Americans and mined for minerals thousands of years ago, many of its darkened miles remained uncharted until much more recently. With caverns so vast and complex, many must wonder how caves like this come to exist in the first place. Read on to learn more.
Image Credit: U.S. National Park Service
Caves form through a variety of processes. Above, for example, is the natural entrance to Carlsbad Caverns in New Mexico. Carlsbad Caverns is believed to have been formed by a unique and interesting process: More than 250 million years ago, this part of the Southwest United States was covered by a shallow inland sea. Within this sea, there formed a colossal, U-shaped reef of minerals, such as calcite, and the residue left behind by sponges and seashells. After this inland sea dried up, the reef was buried by other minerals and became embedded in the Earth's crust. Read on to find out how the process continued.
Image Credit: U.S. National Park Service
This gigantic mineral deposit spent many centuries buried under the surface of the desert, until just a few million years ago, when erosion again exposed the cracked and brittle reef to runoff and seeping rainwater. Because of environmental conditions, the water that poured into the reef's fractures with every rain shower had a lower-than-average pH. Slowly, over the millions of intervening years, this acidic water began to dissolve the reef from the inside, creating vast hollows in the rock. We now know these hollows as Carlsbad Caverns.
Image Credit: U.S. National Park Service
The lowest level of Carlsbad Caverns extends nearly a quarter of a mile below the Earth's surface, and beautiful geologic formations, like the muscular stalagmites of the Hall of Giants (shown above), can be found all throughout the cave system's many passageways and expanses. Mineral features found inside caves, such as stalactites and stalagmites, are known generally as "speleothems."
Image Credit: NPS Photo by Peter Jones
The Devil's Den can be found along the natural entrance route through Carlsbad Caverns. Though the manmade manipulations designed to make the cave safer and more traversable -- such as walkways sheered into the rock, and handrails -- are fairly new, humans have been coming and going from Carlsbad Caverns for more than a thousand years. The cave was extensively explored by a cowboy named James Larkin White around the turn of the 20th century, and subsequently it became both a bat guano mine (these rich mammal feces were sought as a valuable fertilizer) and a U.S. national monument. Before there was a safe staircase leading into the cave, early visitors entered Carlsbad Caverns by riding down in a "guano bucket" at the end of a motorized winch.
Image Credit: NPS Photo by Peter Jones
These geological features are known as the Giant and the Twin Domes, both visible from the Big Room route through Carlsbad Caverns. Though their size makes it hard to believe, stalagmites like these are formed over thousands -- even millions -- of years, one tiny drop of water at a time. When rainwater seeps through the limestone husk of an existing cave system, it soaks up carbon dioxide and calcium bicarbonate from the mineral strata through which it passes. This creates a mineral-rich stream of water, and consequently, when each droplet enters the roof of a limestone cavern and drips to the floor, it leaves a small deposit of calcite on both the spot from which it drips and the spot where it lands. These deposits accumulate over time, creating stalactites on the ceilings and stalagmites on the ground.
Image Credit: NPS Photo by Peter Jones
This is the Rock of Ages, along Carlsbad Caverns' Big Room route. Many of the cave chambers within Carlsbad Caverns National Park (CCNP) have peculiar names. For example, a recently discovered labyrinth of new passageways in CCNP's Lechuguilla Cave is now known as "Oz," with individual rooms bearing titles such as "Munchkin Land," and a pit called the "Kansas Twister." Next, you'll see a cave at the edge of the ocean.
Image Credit: NPS Photo by Peter Jones
A rocky façade of basalt lies set against the ocean at Akun Island -- an unsettled land mass counted among the Aleutian Islands, which curl off the southern coast of Alaska. The Aleutian Islands chain is littered with volcanoes and is considered part of the Pacific Ring of Fire, meaning that you can expect these lands to bear interesting geological features. Click ahead to see a closer view of this cliff face and the cave it holds.
Image Credit: Steve Hillebrand/U.S. Fish and Wildlife Service
The opening you can see kayakers entering above is the mouth of a basalt sea cave, carved into a wall of columnar basalt. Like granite, basalt is an igneous rock, meaning it is forged in the fiery places under the surface and crystallized by the cooling of liquid rock, such as magma or lava. Sometimes during cooling, liquid rock undergoes contractions into disturbingly synthetic-looking columns, like these, which appear to be minutely crafted hexagons and octagons. Check out the next page to see this geometrically prodigious sea cave from inside.
Image Credit: Steve Hillebrand/U.S. Fish and Wildlife Service
Like the limestone caves of Carlsbad Caverns, littoral sea caves like this one are generally formed by water -- though by a much different process. Where solutional limestone caverns are formed by slowly dissolving massive pockets of buried rock, most sea caves are pounded into place by a more straightforward case of mechanical erosion caused by the tide. Here, you can get a great cross-section of the packed honeycomb of basalt columns left behind by ancient volcanic activity.
Image Credit: Steve Hillebrand/U.S. Fish and Wildlife Service
A below-ground waterway cuts through the bedrock of Logan Cave National Wildlife Refuge in the Ozark Mountains of Arkansas. Like Carlsbad Caverns, Logan Cave is a solutional limestone complex, but unlike Carlsbad Caverns, it is relatively small: There are only about 1.5 miles (2.4 kilometers) of charted passageways. Next, you'll see an example of an organism protected by the Logan Cave NWR.
Image Credit: John and Karen Hollingsworth/U.S. Fish and Wildlife Service
Wearing an eerie, all-white exoskeleton, this blind, subterranean crayfish calls Logan Cave home. The cave crayfish is one of several endangered species that the U.S. Fish and Wildlife Service is seeking to protect by declaring the cave a wildlife refuge and closing it to the public. Other important life forms here are the Ozark cavefish and the near-threatened gray bat. See one of Logan Cave's beautiful hidden ponds in the next photo.
Image Credit: John and Karen Hollingsworth/U.S. Fish and Wildlife Service
Natural springs feed the underground stream that flows the length of Logan Cave. This stream passes around 5 million gallons (almost 19,000 kiloliters) of water per day through the cave system, supporting the freshwater life forms that take roost in the dark. Check out another cave-roosting creature in the next photo.
Image Credit: John and Karen Hollingsworth/U.S. Fish and Wildlife Service
This California condor near Hopper Mountain National Wildlife Refuge finds the small overhang at a cave opening useful as a nesting site. Many of the surface-dwelling creatures who seek caves for shelter -- Stone Age humans, for instance -- don't venture far inside, and thus never develop serious genetic adaptations to cave life in the way that the blind cavefish and cave crayfish do. Next: Are there caves on other planets?
Image Credit: Joseph Brandt/ U.S. Fish and Wildlife Service
Images of caves? Beautiful, fascinating, but also pretty creepy. Images of other planets? Much the same -- simultaneously wonderful, exalting and more than a little spine-tingling. So here we reach a curious apex of sensations: the caves of Mars. NASA's Mars Odyssey orbiter created this image of an apparent hole in the surface of Mars that is believed to be the skylight of a cave. How can we tell it's a cave? Unlike the highly volatile and variable surface of a planet, caves have very stable climates. Odyssey's Thermal Emission Imaging System measured the temperature of this apparent hole, compared to the surrounding surface, during both the night and the day. During the daytime, the opening was cooler than the surface of Mars. During the Martian night, the opening was warmer than the surface. This points us toward the naturally climate-controlled conditions of a cave.
Image Credit: NASA/JPL-Caltech/ASU/USGS
NASA's Odyssey has found even more purported cave skylights on the surface of Mars. These six photos come from the slopes of a Martian volcano. What might the world look like to a Martian troglodyte gazing up from these windows to the sky?
Image Credit: NASA/JPL-Caltech/ASU/USGS
No, that's not the Martian stratosphere on a particularly balmy day. We haven't made it to the caverns of the red planet just yet. This is one of the natural surface openings of the Carlsbad Caverns system.
Image Credit: U.S. National Park Service
This is the kind of ceiling you'd hate to notice is slowly lowering in your direction. Though marvelous speleothems can be found in caves all over the world, Carlsbad Caverns is renowned for the shapes and shadows of its limestone formations. In this image, in addition to the hundreds of calcite fangs slowly dripping down from the ceiling, you can also see what look like crystals of dogtooth spar lining the lower regions of the photo. See more of Carlsbad Caverns' haunting natural designs in the next image.
Image Credit: U.S. National Park Service
The rippled curtains of rock visible against this cave wall are known as flowstone, which is a formation created by the flow of calcite-rich water over the wall or slope of a solutional cave. At other places, the combination of erosion and deposition has left this wall with the look of a simmering stone about to boil over.
Image Credit: U.S. National Park Service
Even in the largest and most popular tourist attractions below our feet, new passageways are always being discovered and charted by brave claustrophiles. What underground reaches remain to be explored?
Image Credit: U.S. National Park Service
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