Cave of Swallows 3.69

The Cave of Swallows, also called the Cave of the Swallows, is an open air pit cave in the Municipality of Aquismón, San Luis Potosí, Mexico. The elliptical mouth, on a slope of karst, is 49 by 62 m wide and is undercut around all of its perimeter, widening to a room approximately 303 by 135 meters wide. The floor of the cave is a 333-meter freefall drop from the lowest side of the opening, with a 370-meter drop from the highest side, making it the largest known cave shaft in the world, the second deepest pit in Mexico and perhaps the 11th deepest in the world.HistoryThe cave has been known to the local Huastec people since ancient times. The first documented descent was on 27 December 1966 by T. R. Evans, Charles Borland and Randy Sterns.GeologyThe cave is formed in the El Abra and Tamabra formations, limestones of Middle Cretaceous age. The cave's speleogenesis is still not fully known but is a result of solutional enlargement along a vertical fracture, with subsequent vadose enlargement.EtymologyThe cave's Spanish name Sótano de las Golondrinas means Basement of the Swallows, owing to the many birds which live in holes on the cave walls. These are mostly white-collared swifts (vencejos in Spanish) and green parakeets (periquillo quila), but actual swallows are in fact rarely found here.Each morning, flocks of birds exit the cave by flying in concentric circles, gaining height until they reach the entrance. In the evenings a large flock of swifts circles the mouth of the cave and about once each minute, a group of perhaps fifty breaks off and heads straight down towards the opening. When they cross the edge, the birds pull in their wings and free-fall, extending their wings and pulling out of the dive when they reach the heights of their nests. Watching this has become popular with tourists.