14 Amazing Sinkholes

When people speak of sinkholes, they often refer to the alarming and sometimes tragic occurrences when the ground gives way in the middle of a road and seemingly consumes whatever lies in its path. While such human-accelerated sinkholes are common, as happened with the Great Ravenna Boulevard Sinkhole of 1957, most sinkholes form naturally and more slowly through karst processes, or the chemical dissolution of soluble rocks. A great number of sinkholes are filled with water; due to their depth, they make for great swimming and diving, like the 1,112-feet-deep El Zacatón in Mexico.

From the disastrous to the scenic, here are 14 amazing sinkholes.

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Cenote Ik Kil

The Ik Kil cenote (a cenote is a regional word for a sinkhole filled with groundwater) in Yucatán, Mexico is a circular, aquatic hole with a water surface that is 85 feet below ground level. The Mayans held the Ik Kil cenote as sacred and would use the hole for human sacrifice to the god of rain. Open to the sky, the cenote receives natural sunlight on its milky-bluish-green waters. It's a popular swimming spot—a staircase has even been carved into the limestone for swimmers to reach the water level.

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Montezuma Well

About 11 miles from Montezuma Castle in the Arizona desert lies the Montezuma Well, a limestone sinkhole fed by natural spring water. The well produces so much water on a consistent basis (1,500,000 U.S. gallons each day) that it has been used for irrigation in the area since at least the eighth century. Intriguingly, the Montezuma Well contains at least five species found nowhere else on the planet—the Montobdella Montezuma leech, a diatom, the Hyalella Montezuma amphipod, a water scorpion, and the Montezuma Well springsnail.

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El Zacatón

El Zacatón in northeastern Mexico is the deepest water-filled sinkhole in the world at a depth of 1,112 feet. Named after the floating island topped with zacatón grass that moves across the water’s surface, El Zacatón is part of a group of 15 sinkholes in the region, and their formation is thought to be connected to volcanic activity. Due to its extreme depth, the sinkhole is popular among divers. In 1993, Dr. Ann Kristovich set the women’s depth record when she dove 554 feet down into El Zacatón.

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The Great Ravenna Boulevard Sinkhole

On November 11, 1957, in a quiet residential neighborhood along Seattle’s Ravenna Boulevard, a gigantic hole opened up and engulfed a portion of the street, a large chestnut tree, and a 30-foot telephone pole. The massive crater was measured to be 60 feet deep, 120 feet in width, and over 200 feet long—consuming more than a thousand cubic yards in all. The disaster is believed to have been triggered by a broken sewer line. While no casualties were observed, residents of 10 nearby homes were evacuated out of their back doors to safety.

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The Great Blue Hole

Formed during the ice age, the Great Blue Hole off the coast of Belize is a circular marine sinkhole in the center of an atoll, or ring-shaped coral reef. The sinkhole is part of the Belize Barrier Reef Reserve System, a UNESCO site, and measures 407 feet deep and 1,043 feet across. Popular among scuba divers for its clear waters, the Great Blue Hole is home to marine life including the Caribbean reef shark and midnight parrotfish.

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Bimmah Sinkhole

The Bimmah Sinkhole on the southeastern coast of the Arabian Peninsula in the country of Oman is a water-filled hole of sunken limestone. The famous sinkhole measures 164 feet wide by 230 feet long and has a depth of about 65 feet. Once believed to have been formed by a meteor, the sinkhole gets its Arabic name, “Hawiyyat Najm,” from the phrase “the deep well of the falling star.” Today, Bimmah Sinkhole is the focal point of Hawiyyat Najm Park and has a concrete stairway leading down to the water’s surface.

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Numby Numby

Numby Numby in the Northern Territory of Australia is a hot spring-fed sinkhole that has an average temperature of about 90 degrees. Popular among swimmers, the desert pool reaches an astonishing 200 feet deep just a few feet from its edge. Indigenous peoples in the area call it Ngambingambi, and a widely told legend holds that the sinkhole formed when a subterranean deity known as the Rainbow Serpent burst through the ground in a rage.

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Dean's Blue Hole

One of the deepest water-filled sinkholes in the world can be found near Clarence Town on Long Island in the Bahamas. Known as Dean’s Blue Hole, the sinkhole reaches 663 feet deep and has a diameter of 85 feet to 115 feet at water level. The width of the hole expands considerably to 330 feet 66 feet beneath the surface. Each year, the international freediving competition Vertical Blue is held at Dean’s Blue Hole.

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Xiaozhai Tiankeng

Xiaozhai Tiankeng in China is the world’s deepest sinkhole at somewhere between 1,677 and 2,172 feet deep. Sometimes referred to as the Heavenly Pit, the massive sinkhole was formed on top of a cave and features a 5.3-mile underground river that runs through it. The impressive geological wonder has a 2,800-step staircase carved into its side in an effort to attract tourists to the area.

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Cave of Swallows

The Cave of Swallows is 160 feet wide by 203 feet long at its mouth and widens considerably to 442 feet by 994 feet within the hole itself. At 1,214 feet deep, the Cave of Swallows is the second deepest sinkhole in Mexico. The large sinkhole gets its name from the flocks of birds that live in the holes along its limestone walls. Although swallows are rarely seen within the opening, green parakeets and white-collared swifts can be found there in abundance.

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Padirac Cave

Padirac Cave, or Gouffre de Padirac in French, is a 338-feet-deep limestone sinkhole in southwestern France. The stunning chasm contains an underground river system that can be navigated by boat. Each year, over 350,000 people visit Padirac Cave and descend a 246-foot staircase for a tour of its galleries. One of the most impressive rooms within the cave is the Great Dome Hall, which reaches a staggering height of 308 feet.

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Red Lake

Red Lake is a lake-filled sinkhole in Croatia and is named after the surrounding reddish cliffs. It is commonly thought that the sinkhole was formed when the ceiling of the cave below collapsed. Best estimates show that Red Lake has a volume of between 82 million and 92 million cubic feet, making it one of the largest known sinkholes in the world. A small fish species known as the spotted minnow lives in the underground lake and various nearby springs.

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Blue Hole of Dahab

The Blue Hole of Dahab is a 393-foot-deep sinkhole in Egypt on the coast of the Red Sea. Coral walls surround the hole, where Red Sea bannerfish, sea goldies, and butterflyfish find protection. The resort town sinkhole has been a renowned diving location for decades due to its lack of a current and its incredible depth so close to the shoreline. Despite its popularity among divers, the Blue Hole of Dahab has taken the lives of many who’ve gone into its waters. In particular, an 85-foot-long tunnel known as “The Arch” has trapped and drowned many seeking to swim through it.

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Sima Humboldt

In the remote Cerro Sarisariñama mountains on Venezuela’s southwest border lie four sinkholes known collectively as the Sarisariñama Sinkholes. Sima Humboldt, the largest of the group, is 1,030 feet deep and 1,155 feet wide. Due to its extremely isolated location, the massive sinkhole wasn’t explored until 1974 when a helicopter lowered dozens of researchers onto the forested site. To this day, the 640-million-cubic-foot Sima Humboldt is inaccessible to the public.