That Sinking Feeling: Exploring the Earth’s Largest Holes

Featured — By Zain Iqbal on June 10, 2010 at 2:56 pm

Ever get the feeling that the terra firma you’re standing on isn’t as stable as you’d hope? Out here in California, we have to worry about earthquakes shaking us up; and if you happen to live in Guatemala, it seems that sinkholes are the new urban danger. Fortunately, no one died when 100 feet of earth collapsed in Guatemala City in May of 2010, but the amazing images from the sink prompted people to wonder, and worry, more about them.

So what is a sinkhole? It is basically a natural depression caused by the erosion of limestone by groundwater. Sinkholes can either form over time or in rare cases like the ones in Guatemala, may occur suddenly. Whether the hole is earth-made – or in some cases may appear to be a sinkhole, but is actually caused by man – here are a few that have turned the heads of divers, climbers, and explorers around the world.


The largest sinkhole in the world is part of five interconnected cenotes (a Mayan word that describes a sinkhole filled with groundwater) in northeastern Mexico. The largest of the Zacatón sinkholes plunges almost 1,100 feet into the earth, enough depth to submerge three Statues of Liberty.

Image: e_garza/Flickr and University of Texas

The strangest feature of the largest Zacatón cenote are the “islands” that float around at the top of the sinkhole’s waterline. These large, circular mats of lush, green reeds were probably formed by seedlings that attached to stray amounts of calcium carbonate from the sinkhole walls. Because of the depth of Zacatón, NASA has tested an aquatic mapping probe that may someday be used in the exploration of Europa, a moon of Jupiter that may have a vast ocean under its icy crust.

Sima Humboldt and Sima Martel

High up on the summit of the  Sarisariñama tepui – a plateau in Bolivar, Venezuela – are two massive sinkholes discovered by a pilot who flew overhead in 1961. Because of their remote location, both Sima Martel and Sima Humboldt were first explored as in the mid-70s, during which scientists discovered a unique weathering process which carved them as well as the formation of forest at the bottom of each sinkhole.

Image: Wikipedia and Google Maps

Post both of these to your “to explore in the future” list, as both sinkholes are currently off-limits to tourists and may only be explored by speleologists (that’s a cave and karst researcher to us laypeople.) In fact, Sima Martel was named after the so-called “father of modern speleology,” Édouard-Alfred Martel. The larger Sima Humboldt was named after German explorer and naturalist Friedrich Wilhelm Heinrich Alexander Freiherr von Humboldt.


Recreational divers may max out at 100 feet on any given dive, but when it comes to ultra-deep diving, these adrenaline junkies try to go deeper than 660 feet down – the limit of surface light penetration into water. One of the eeriest stories ever to come out of a deep dive happened in 2005 during a expedition in South Africa at Boesmansgat, also known as Bushman’s Hole, purported to be the 3rd deepest submerged sinkhole in the world.

Image: Green Kalahari

Boesmansgat became well-known among the adventure community in 2005, when well-known Australian deep diver David Shaw attempted to descend 800 feet to recover the body of Deon Dreyer, another diver who lost his life 11 years prior. Outside magazine featured the chilling story, which ended up taking the life of Shaw, but resulted in the recovery of both his and Dreyer’s body. Even though these two incidents cast a shadow over Boesmansgat, it is still a popular destination for divers and explorers alike.

Great Blue Hole

One the most famous diving spots in the world lies off the coast of Belize within the Lighthouse Reef. The Great Blue Hole is a UNESCO World Heritage Site and one of the world’s most recognizable blue holes— a type of submarine cave or sinkhole usually found within reef formations. The seemingly perfect circle of coral descends over 400 feet and is home to a number of different shark species.

Image: joself/Flickr

The famous ocean explorer Jacques Cousteau claimed the Great Blue Hole as one of the best diving sites in the world after he charted the area in 1971. Today, recreational divers often make the day-long trip from Ambergris Caye to the Lighthouse Reef to explore the Great Blue Hole, using it as a jumping spot for other dives along the Belize Barrier Reef.

Blue Hole

Another undersea sinkhole popular with divers is off the coast of Egypt near the diving resort of Dahab. Blue Hole (not to be confused with the Great Blue Hole in Belize) has jagged coral features and is home to a number of fish and wildlife native only to the Red Sea. The unique limestone formations within Blue Hole, however, are what lure recreational divers into a false sense of security, including an underwater tunnel known as “the Arch.”

Images: WhitecombeRD and .Angeli/Flickr

Divers who attempt to swim through the 17o foot deep Arch are passing far deeper than the recreational diving limit of 130 feet. Because of this, a number of accidents have occurred at here, earning Blue Hole the notorious nickname of the “Diver’s Cemetery.” Still, those who aren’t interested in testing fate can easily explore around the rim of Blue Hole, including a unique “saddle” feature which separates the sinkhole from the open water of the Red Sea.

Big Hole

When diamonds were discovered in what is now South Africa in 1871, tens upon thousands of miners scrambled to a spot that would soon be known as Kimberley in search of riches. For over 40 years the site was excavated by hand, reaching a depth of over 700 feet, with miners discovering almost 6,000 pounds of diamonds in the process. De Beers eventually took the mining process underground, excavating a full 3,500 feet below the kimberlite pipe, but the Big Hole remains as a reminder of the initial diamond rush.

Image: jrcohen and Lmeylan/Flickr

Sure, the Big Hole isn’t a traditional sinkhole, but it remains the deepest hand-dug mine in the world. A rival mine in nearby Jagersfontain claims to the be the biggest by volume, but because of the history surrounding the Big Hole, it remains a popular tourist destination in South Africa. Big Hole is currently vying for recognition on the UNESCO World Heritage Site list.

Door to Hell

Not exactly man-made, but not strictly Earth-made either, this strange formation in the middle of the Karakum desert in Turkmenistan was the result of a mining accident in 1971. Soviet geologists discovered an underground cavern while doing an exploratory dig for natural gas. Unfortunately, the roof of the cavern collapsed, resulting in a large hole about 325 feet across. Officials attempted to burn the gas away, thinking it would flame out within a few days, but almost 40 years later, the fire is still burning with locals now dubbing the hole the “Door to Hell.”

Images: flydime/flydime/Flickr

The bizarre features of this fiery cavern certainly make it look like it is aptly named: a doorway to hell. The 350 villagers of Derweze, which is about 160 miles north of Turkmenistan’s capital Ashgabat, probably make a nominal bit of cash off visitors who swing by this remote site. Still, the days of the Door to Hell seem numbered, as the Turkmenistan government is eying to seal the hole in order to make natural gas exploration more attractive to investors.

Guatemala City “Sinkhole”

When these images first appeared in the media, it looks as if these perfectly-round holes dropped straight through into the center of the Earth. Some scientists say these aren’t true sinkholes as much as they are “piping features,” – the result of the Guatemala City being built on porous pumice instead of solid bedrock. The bottom line is they are a fairly frightening example of what could happen after strong runoff from the occurrence of a water-main burst or even the torrent from a hurricane.

Image: horslips5/Flickr

Know of any interesting sinkholes that we missed out on? Leave a comment and let us know!

Tags: erosion of limestone, Guatemala, holes, i feel the earth move under my feet, sinkholes, zacaton


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