Abîme

An abîme is the geographical term for a vertical shaft in karst terrain that may be very deep and usually opens into a network of subterranean passages.

Abîmes are a structure which form late in the life of a limestone cave. They can be 1–10 meters in diameter and up to 50 meters in height vertically. The walls have grooves that serve as a contrast to the smooth nature of the rest of the cave. They are known to lie under heads of stream valleys, sinkholes, or along non-carbonated rocks. Water will occasionally fall down the shaft, creating subterranean waterfalls. Only a small portion of the abîme connects to the rest of the cavern. They can extend to the present water table, while the rest of the cavern lies above it.

Abîme are also known as pit caves in the U.S. and pot caves in England. They can also be called domepits, due to the way that looking up from below a dome can be seen and looking down from above a pit is seen. Blue Holes are sinkholes that have filled with water and can occur on land or at sea. In Central America, they are called cenotes.

This is the act of using ropes, harnesses and ladders to descend an abîme. This is the most popular activity besides the actual exploration of caves. It is also the most dangerous activity to do in a cave. The biggest danger comes from using poor ropes and ladders for rappelling down shafts. Many amateurs make this mistake and it leads to the most cave deaths.

An extreme sport and requiring a person too stand at the entrance of an abîme and jump into the opening while pulling a parachute before hitting the cave floor. This is highly dangerous and should only be partaken by those with experience. The Cave of Swallows is the most popular due to its 333 m. (1,094 ft.) freefall drop which is the longest in the Western hemisphere.

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