Sinkholes, also known as shake holes or swallow holes, occur when water seeps into solid bedrock and erodes it to the point that an underground cavity forms. When this cavity collapses, it forms a crater-like depression. Sinkholes occur all over the world — in jungles as well as cities — and can appear suddenly or gradually. The Bimmah Sinkhole, above, is located on the coast of Oman, an Arab state in the Arabian Peninsula.
In geologic terms, a sinkhole happens as a result of the karst processes, or the chemical dissolution of carbonate rocks. Carbonate rocks, such as limestone, are porous to varying degrees because they contain tiny holes that can absorb water. Too much absorption of fluid can cause the rock to give way and create a hole in the surface topography. This tropical sinkhole, captured from the bottom looking up to its surface, is in Yucatan, Mexico. Over time, vegetation has grown over the mouth of the sinkhole.
Cenote Dzitnup is also located in Mexico's Yucatán Peninsula. Underground, freshwater-filled sinkholes with openings shinning through at the top like this one are known as cenotes in Mexico and Central America.
Although it's known as the Montezuma Well Sinkhole, this sinkhole, located in Arizona's Montezuma Castle National Monument near Camp Verde, Ariz., looks more like a lake than a well. The indents on the land's surface formed by sinkholes can look like hollow craters or fill up with water and become lakes or ponds, depending on surrounding geological conditions.
This massive sinkhole is located in Mount Gambier, South Australia, and was formed by acidic groundwater eroding the area's porous limestone. The region contains many water-filled caves and sinkholes, but the Mount Gambier sinkhole has become an Australian landmark, and was even turned into a beautiful recreational garden for the general public and tourists.
Found along the Soldier Pass hiking trail in Sedona, Ariz., the Devil's Kitchen sinkhole gets its sinister name from its red walls, which are made of sandstone. It reportedly first collapsed in the early 1880s, with a second historical collapse in 1989. The relatively young sinkhole's features are so angular because the surfaces of its rocks' edges have not yet been sloughed dull. The large rectangular rock toward the center is known as the Grand Piano.
The Bimmah Sinkhole is near Dibab village in Oman, an Arab state in the Arabian Peninsula. A winding stone staircase leads down to the sinkhole, which is a beautiful aquamarine and emerald color, with the darker green hues resulting from algae growth in the water.
Here's another view of the Bimmah Sinkhole, which was created when a limestone cavern collapsed. However, local folklore states that a chunk of the moon fell from the sky and formed the hole when it hit Earth. Residents refer to the sinkhole as "Bait al Afreet," or the "House of the Demon," although with its tranquil azure waters, it looks quite heavenly.
Pictured above is what's known as a "blue hole," or an underwater sinkhole, located in the Lost River Cave and Valley of Bowling Green, Ky. The result of an underground, dissolved limestone drainage system that rests beneath the region, the blue hole is surrounded by local myths of swimmers disappearing below its murky, stagnant surface, never to return. [Gallery: Lost in the Bermuda Triangle]
Located in Green County, east of Bowling Green, Ky., this sinkhole formed about eight years ago; the owners of the farmland where it formed have since pushed old hay rolls into the hole, where a tree has already begun to grow. The walls of the sinkhole are a rich, rusty color, characteristic of the reddish-brown colored silt and dark red clay of central Kentucky's soil.
The photographer snapped this aerial photo of the Melchor de Mencos sinkholes while flying over Petén, in the northern part of Guatemala. These twin cenotes are located near Lake Macanche and are surrounded by a thick rain forest.
Located in the city of Imotski, Croatia, the Red Lake is named for the reddish-brown color of the iron oxides in its surrounding cliffs. The pit, which has become a lake, is lined with nearly vertical walls. As one of the largest sinkholes in the world, it is about 1,700 feet (530 m) deep.
Yet another sinkhole with a demonic name, the Devil's Hole in Hawthorne, Fla., is about 100 feet (30 meters) deep. It’s also known as the Devil's sink and is a popular spot for locals and even has a rope swing and two jumping platforms. Originally the site of a limestone dig, the sinkhole has an underwater entrance leading to a cave system that few divers dare to explore.