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Cave divers explore a flooded chamber of Florida's Diepolder Cave, 250 feet (76 meters) below the Earth's surface. Named after the man who originally owned the land, Diepolder Cave is located on Sand Hill Boy Scout Reservation near Brooksville, Florida.
Lava-tube caves, like this one in California's Lava Beds National Monument, are found throughout the world. These unique underground structures form during long-lasting lava flows. As lava moves through a channel, overflows build natural levees along the sides, which can eventually connect and harden, forming a canopy. Just as a winter stream continues to flow beneath its ice cap, lava continues to move under this roof. When flow from the source stops, the remaining lava moves through to the end, leaving a hollow tube, often large enough to walk through.
A spelunker in a glacier cave in Greenland gazes upon colors and shapes that look more like a swirling galaxy than a cave formation. The otherworldly contours of this ice chamber were formed by the heat of a geothermal spring.
A caver is dwarfed by calcite columns that stretch some 50 feet (15 meters) to the top of Tower Place in Lechuguilla Cave. Located in Carlsbad Caverns National Park in New Mexico, this famous cave attracts spelunkers from all over the world.
Mineral deposits in caves can create amazing shapes, such as these chocolaty-looking cave pearls. These unique spherical formations are created in cave pools when layers of calcite are slowly deposited around a grain of sand or dirt.
Mexico's Cueva de los Cristales (Cave of Crystals) contains some of the world's largest known natural crystals—translucent beams of gypsum as long as 36 feet (11 meters).