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Hidden Marvel: Vietnam’s Son Doong Cave Reveals Its Secrets After Years Of Discovery

Vietnam's Son Doong Cave: The World's Largest Cave with Its Own Weather System and Rare Species.
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Hidden behind treacherous mountains deep in the tropical forests of a national park in Vietnam, the world’s largest cave sat untouched and sealed up for millions of years–until just recently.

A tourist looks at stalactites and stalagmites inside the Phong Nha Caves. The caves can be found near the Phong Nha Nature Reserve. The Vietnamese Government is proposing that this Nature Reserve become a World Heritage Site. The nature reserve contains a rare species of Langur. These Langur can only be found in this small region of Vietnam. (PETER CHARLESWORTH/GETTY IMAGES) 

Clouds billowing out from the entrance of the cave and the sounds of a raging river caught the attention of Ho Khanh, a local man who was searching for shelter from a storm in the Phong Nha-Ke Bang National Park while foraging for food and timber to earn a modest income in 1990, according to Oxalis Adventure, a local tour company that leads expeditions in the area.

Little did Khanh know that he had just discovered an opening in a limestone cliff that led to the planet’s largest cave, which is so big that it has its own weather system along with underground rainforests, never-before-seen animals and rock formations called stalagmites the size of tall buildings.

Unaware of the magnificent hidden world concealed just feet away, he returned home and forgot about what he had just stumbled upon, the tour company reports.

The memory and location faded until five years later when he was hired as a guide for cave expert Howard Limbert with the British Cave Research Association (BRCA). Limbert and his team were in the area conducting exploratory caving expeditions since they knew that a sizable cave likely existed within central Vietnam’s Phong Nha-Ke Bang National Park. The U.K. team led three expeditions to find the cave – and failed every time.

Trying to explain what he had seen, Khanh drew pictures in the sand of the clouds, the cave entrance and the water since he spoke very little English. This gave Limbert the clues he needed. Now Limbert was sure that they, in fact, had a colossal cave on their hands.

After they heard Khanh’s stories, they urged him to rediscover this underground world.

Alone, Khahn set out to find the secluded cave entrance once again. For a week, he wandered in the jungle, notching trees to mark his path along the way. The cave entrance was so elusive, Khanh could not remember its exact location.

The quest to re-locate the cave lasted longer than a decade, but Khahn was determined to find it once again. After several attempts, he finally found the same spot in 2008 — 18 years after he’d first discovered it.

When Limbert returned to Vietnam in 2009, Khahn told the cave researcher he had done it. He finally found the cave.

Khahn led the team of caving professionals to the opening of what is now known as the Son Doong cave. A narrow entrance awaits adventurers looking to explore the cave, but those without headlamps won’t get very far as only darkness makes it all but impossible to see without artificial light.

“When we entered the cave during our early exploration in 2009, we had no idea we had discovered the largest cave in the world,” Limbert told AccuWeather in an interview. “What we did realize was that Son Doong was so very different from any other cave we had explored before.”

At its highest point, Son Doong’s ceiling rises to an unfathomable 650 feet (198.12 m) , which, for scale, is more than twice the height of the Statue of Liberty.

“After we had completed our surveys, it became apparent that Son Doong is the largest cave in the world. The original explorations were long and tough, the first team exploring for 22 hours caving and mapping the cave,” said Limbert.

And it could get even bigger.

Cave experts are researching the connection between Son Doong Cave and neighboring Thung Cave. If the connection is made, Son Doong will be the largest cave in the world by volume, as well as by cross-section.

Apart from its immense size, the ancient cave has two dolines, or areas where the cave ceiling collapsed millennia ago allowing light to enter the cave from skylights more than 650 feet (198.12 m) above. Over time, the dolines let in light, rain, soil and seed which all combined to create a micro “jungle.”

At the base of the dolines, jungles are present with countless rare plants that surround trees that stand up to 160 feet (48.77 m) tall. Incredible sunbeams enter the cave, giving light to the jungles and illuminating huge rock formations, called stalagmites, that rise from the floor. The stalagmites are created by the accumulation of material deposited on the floor from ceiling drippings.

Arguably one of the most spectacular occurrences in the cave is a weather phenomenon many might not expect to find in a cave-clouds.

“When the heat reaches inside the cave, it evaporates the water generating ‘clouds’ inside the cave,” Josh White, a cave safety expert and guide with Oxalis Adventure, told AccuWeather in an interview. “The airflow of the cave varies depending on the pressure and temperature outside each of the four main openings,” he explained, adding, “This can suck this cloud into the darker sections of the cave.”

There are periods of time when the cave is devoid of clouds.

“During the winter months, there are no clouds in the cave,” said Limbert. “It is crystal clear. At this time, the cave temperature is warmer than the outside temperatures.”

The cave temperature is always 73 degrees Fahrenheit, regardless of the season or temperature outside the cave.

“When spring arrives, so do the clouds. These, we believe, are created within the cave,” said Limbert. “The heat that comes down the dolines hits the river and clouds are made. We can see this clearly near our first camp near doline one.”

A stagnant temperature and clouds inside a cave are not entirely uncommon sensations, as AccuWeather Meteorologist Matt Benz explained.

“Many caves have nearly year-round temperatures that fluctuate very little with the changing seasons,” said Benz. “When outside air masses come in contact with a cave air mass,” he continued, “it can lead to things like clouds. To make a cloud, you need a moist air mass that has cooled down to the saturation temperature. Basically, that’s the point where the air becomes saturated, and you can see things like clouds or dew forming.”

In the summer, Benz said a warm, moist air mass can sneak into a cave through an entrance and transform into a cloud when it is cooled.

“You can also get wind in a cave which develops as the air pressure outside the cave changes, which leads to an equalization of pressure inside the cave in the form of a breeze or wind. Wind Cave in the Black Hills of South Dakota is an example” of this, Benz said.

Wind flowing to and from the cave entrances blows the clouds through the cave. Limbert said this is one spectacular sight to behold. When the cloud hits the roof of the cave, which is often higher than 300-500 feet, droplets of water fall everywhere simulating rain, a very rare occurrence within caves.

On top of the unique weather system, scientists from Hanoi University with Limbert’s team discovered seven new species of animals living in the cave. Those seven species are not seen anywhere else in the world, only in Son Doong. These rare animals include white fish, white spiders and white centipedes. They have also discovered a 400-million-year-old fossil made from coral.

“Son Doong is really a unique place on this planet,” Limbert said, “It really is an incredible experience. It, however, is not a walk in the park. Some degree of fitness is expected but not caving or climbing experience.”

Jonathan Hudson and Marina Hudson were lucky enough to have entered the cave. Marina Hudson added it to her bucket list after reading an article about the cave on National Geographic. The couple, from La Jolla, California, booked the trip a year in advance and set out to check it off their bucket list in the spring of 2019.

“I just remember thinking, ‘Wow! That looks so incredible and different from anything we’ve done.’ We were thinking about what do we want to do before we have kids, and I knew I wanted to go to Vietnam and track that cave because it looked so different from any other track or expedition we’ve done,” said Marina Hudson telling AccuWeather.

And, sure enough, it was.

To get to the cave, they hiked for three to four hours, Marina said. Once they made it, they spent three days in the cave and even went swimming in a river inside the cave, which was nice for cooling off, Marina said, because it was very hot and humid inside with mist.

“Oh gosh, it’s just so big; it’s like a city underground. There are just so many different areas from where the ceiling has collapsed,” said Marina in her recollection.

“There is one part of the cave that you have to take a boat to cross, but when we were inside, there wasn’t that much water, so there was just a tunnel of mud. When I tried to walk, the mud came all the way up to my knees,” said Marina.

As far as animals and plants go, Marina recalled seeing some very large centipedes that were about a foot long.

Adventurers wanting to see this spectacular work of Mother Mature for themselves should be advised: It’ll also cost a pretty penny. The four-day tour is $3,000 per person — and does not include airfare and other expenses associated with traveling to Vietnam. Plus, there is a long waiting list. Only 1,000 people are allowed in over a one-year period due to conservation efforts, and Oxalis Adventure is the only company with permission to take travelers inside.

People travel from all over the globe to witness this one-of-a-kind natural wonder.

“Nowadays, adventure tours visit the cave on a four-day traverse through the whole giant main passage supported by a porter team of 30 people including cave experts involved in the original exploration,” said Limbert.

These adventure tours have created employment for many local people, and the area is now the fastest-growing tourism destination in Vietnam. For more visuals from inside the remarkable cave, watch the video below.

Produced in association with AccuWeather

Edited by and

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