Cave explorers from Oman have become the first individuals to descend to the bottom of the 367-foot (112 meters) deep "Well of Hell" sinkhole in Yemen, which many local people believe is a genie-infested gateway to the underworld, according to news reports.
The natural sinkhole, officially known as the Well of Barhout, has an eerily circular entrance that spans 98 feet (30 m) in diameter and is located in the middle of the desert in al-Mahra province in eastern Yemen, close to the border with Oman. Amateur cave explorers have entered the sinkhole before, but until now nobody was known to have made it all the way to the bottom.
Last week, a team of 10 explorers from the Omani Caves Exploration Team (OCET) explored the Well of Barhout using a pulley system that lowered eight of the members to the bottom while the remaining two stayed at the top. A small crowd of intrepid spectators gathered to watch the event, despite local fears surrounding the sinkhole. A video of the explorers descending into the cave was shared by the BBC.
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"Passion drove us to do this," Mohammed al-Kindi, a geology professor at the German University of Technology in Oman who was part of the OCET team, told French news agency AFP. "And we felt that this is something that will reveal a new wonder and part of Yemeni history."
The explorers reported finding waterfalls, snakes, dead animals, stalagmites and cave pearls, but unsurprisingly they did not find any genies or a doorway into hell.
The exact age of the Well of Barhout is currently unknown, but it is likely millions of years old, according to AFP.
Many local myths have sprung up to explain the sinkhole, most of which describe it as a prison for jinn, or genies, which causes bad luck as a result. Some people also believe that if they get too close, the sinkhole can pull people inside; others claim that the gaping hole is a supervolcano capable of destroying the Earth, according to AFP, although there is no scientific evidence to back this up.
In the past, people have also reported a foul smell rising from the large hole, something that spurred stories about it being a gateway to hell, leading to its nickname.
However, in reality, the Well of Barhout is a fairly typical sinkhole.
How sinkholes form
"There are different types of sinkholes," Philip van Beynen, a sinkhole expert at the University of South Florida who was not involved in the exploration, told Live Science. "The most common are collapse and subsidence sinkholes."
Related: See wild photos of gaping sinkholes
Collapse sinkholes form when voids in the bedrock below the surface expand so much that the roof above is no longer supported, and the rock and overlying sediment suddenly collapse into the cave. Subsidence sinkholes occur when surface sediments slowly trickle down into small voids below the ground until a depression or sinkhole forms, van Beynen said.
Both rely on a special type of landscape, known as karst, characterized by carbonate bedrock like limestone and dolomite, which is soluble in water and leads to caves, springs and sinkholes, van Beynen said.
Unfortunately, it is hard to tell exactly how or when sinkholes form, he added. "Unless it occurs when people live at the site and record the event, then it's almost impossible."
Exploring the cave
As the OCET team descended into the sinkhole, they arrived on an uneven and jagged floor covered in stalagmites, some of which reached 30 feet (9 m) tall, according to Omani newspaper Muscat Daily. Some parts of the floor were also covered in cave pearls, which are also a type of speleothems — structures in caves, such as stalagmites and stalactites, that form from the gradual build-up of minerals, such as calcium carbonate, from dripping water.
"They [cave pearls] form from dripping or flowing water as concentric layers of mineral, usually around some kind of a nucleus," Leslie Melim, a geologist at Western Illinois University who specializes in cave pearls, told Live Science. "Practically, anything can act as a nucleus, whatever is present in the cave or mine. Since the nucleus is loose, minerals can grow entirely around the grain, which starts a pearl forming."
Cave pearls are uncommon and can grow only on parts of a cave floor that are completely flat so that the nucleus doesn't move around, Melim said.
From inside the sinkhole, the team also discovered that water emerges from several holes in the cave walls at around 213 feet (65 m) below the surface, creating small waterfalls, according to Muscat Daily. This provides the dripping water needed for a the speleothems, stalagmites and cave pearls, to form, Melim said.
The explorers also reported seeing snakes, frogs and beetles inside the cave system, as well as several dead animals, mainly birds, that appeared to have fallen inside the pit. The rotting corpses could have caused the stench reported by locals, but "there was no overwhelming bad smell" inside the sinkhole, al-Kindi told AFP.
The team took samples that may also reveal further information on the sinkhole and how it formed. "We collected samples of water, rocks, soil and some dead animals but have yet to have them analyzed," al-Kindi told AFP.
A final report on the exploration of the Well of Barhout is expected in the coming weeks.
Originally published on Live Science.
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Harry is a U.K.-based staff writer at Live Science. He studied Marine Biology at the University of Exeter (Penryn campus) and after graduating started his own blog site "Marine Madness," which he continues to run with other ocean enthusiasts. He is also interested in evolution, climate change, robots, space exploration, environmental conservation and anything that's been fossilized. When not at work he can be found watching sci-fi films, playing old Pokemon games or running (probably slower than he'd like).