00:00Imagine you are walking to your car in the morning, but there is a problem.
00:04Your vehicle is not sitting neatly by the side of the road.
00:08Its rear end is sticking out of a gaping hole.
00:11This is what happened to a Queens resident, New York, back in 2020.
00:16A sinkhole had swallowed his SUV overnight.
00:20Events like this are nothing out of the ordinary in many parts of the globe.
00:23But sometimes, sinkholes can hide unspoken beauty inside them.
00:28In East Asia, a recent find stunned the scientific community.
00:33Cave explorers came across a colossal sinkhole that concealed an ancient forest.
00:38It is located in a province, Guangxi Zhuang, close to the north of Vietnam, the Lay County,
00:45where researchers discovered the hidden forest is already famous worldwide for sinkholes.
00:51This one brings the number to 30.
00:53They are scattered over an area the size of three Gibraltars.
00:57This is just a tenth of the total number of sinkholes in the whole country.
01:02The name Tiankeng for these large holes in Earth's surface translates as sky holes or
01:08heavenly pits.
01:10The dimensions of the new sinkhole are impressive.
01:13It is over a thousand feet long, and it's pretty deep too.
01:17You could fit the Great Pyramid of Giza one and a half times inside it.
01:21The sinkhole's total volume matches that of 2,000 Olympic swimming pools.
01:26The exploration team had to hike for hours to reach the bottom.
01:30It was all worth it in the end.
01:32They discovered a pristine underground forest that had no trace of human activity.
01:38Scientists estimate that the plants date back to the time of the dinosaurs.
01:42The foliage reached to the explorers' shoulders.
01:46Some trees were two times taller than the Hollywood sign.
01:49This discovery was amazing, but not entirely unexpected.
01:53Geologists were familiar with this type of landscape.
01:57In this part of East Asia, karst topography is pretty common.
02:01The word is Slavic in origin.
02:04Since the late 19th century, geologists have been using it to describe barren limestone
02:09regions.
02:11This type of landscape features fissures in the ground, caves, underground streams, and,
02:16of course, sinkholes.
02:19It forms in parts of the world with heavy rainfall.
02:22The water dissolves materials such as limestone or dolomite.
02:26This creates a scenery that many people describe as wild beauty.
02:31Karst terrains have a practical purpose as well.
02:34They are ideal for storing water that humans can drink.
02:38Around 700 million people around the world use these karst aquifers as their primary
02:43water source.
02:44In the United States alone, 40% of the groundwater used for drinking comes from them.
02:50Springs of Florida and the Mammoth Cave in Kentucky are just some of the most famous
02:55karst areas.
02:57Geologists classify around a fifth of the U.S. land surface as karst.
03:02This type of terrain exists on other continents as well, in the Caribbean, Europe, Australia,
03:08and Asia.
03:09Due to local differences in climate and geology, karst doesn't appear the same everywhere.
03:14In the Spanish province of Malaga, the landscape consists of barren rock.
03:19This is what the karst regions of Italy, Slovenia, and Montenegro also look like.
03:25In East Asia, the landscape over the karst is green.
03:29This is because of the humid tropical climate.
03:32Sinkholes and cave entrances are usually hidden behind lush vegetation.
03:37The region's unique appearance got it inscribed on the UNESCO's World Heritage List in 2007.
03:44The world's second most populous country is home to two-thirds of the planet's natural
03:48occurring sinkholes, tiankengs.
03:52They start to form when rainwater seeps into cracks in the limestone.
03:56Over time, the gaps widen as more and more material is washed away.
04:01At one point, the ground above the limestone becomes unstable.
04:05The end result is the collapse of the surface layer.
04:08This happens suddenly and without prior warning signs.
04:12Once a hole forms in the ground, water starts filling it up.
04:16Another way for a sinkhole to form is the existence of an underground cave.
04:20Its roof can collapse.
04:22The shape of such sinkholes resembles a funnel.
04:25It is wider at the opening on the top and narrower near the bottom of the pool.
04:31The most famous of these sinkholes are cenotes.
04:34They occur naturally on the Yucatan Peninsula in Mexico.
04:37The region is home to more than 2,000 cenotes.
04:40They are all former caves whose roofs had collapsed at some point in time, and they
04:45are filled with fresh water.
04:47The local people have been using them as water sources for thousands of years.
04:51The ancient Mayas gave them mystical symbolism.
04:54For them, the cenotes were passageways to the other world.
04:58In reality, they are just a feature of Karst terrain.
05:02Sinkholes that form in regions with abundant rainfall and limestone beneath the surface
05:06soil.
05:08The depth of a sinkhole can vary significantly.
05:11The smallest are barely three feet deep.
05:14When it fills up with water, it turns into a pond.
05:17A large lake can form in the place of a large sinkhole.
05:21One example is the Red Lake in Croatia.
05:23The most impressive thing about it are the steep cliffs that rise above the lake.
05:28They are nearly 800 feet tall.
05:31The world's biggest and deepest sinkhole, Xiaoshai Tiankeng, lies in the vicinity of
05:37the Yangtze River.
05:39The outside world discovered it only in 1994.
05:43The hole is so deep that you could stack up seven statues of liberty inside it.
05:48During the rainy season, a waterfall cascades from the pit's mouth into a cave system at
05:54the bottom.
05:55But not all sinkholes fill up with water.
05:59This was the case with the newly discovered Giant Sinkhole in Asia.
06:02It developed its own ecosystem.
06:05The high humidity and low temperature inside it were perfect for plant life to thrive.
06:11The very bottom of the hole is connected to an underground water flow.
06:17Scientists discovered 72 species of rare wild plants in the area.
06:22They are in danger of disappearing on the surface.
06:25But inside the sinkhole, they have found the perfect conditions for growth.
06:30The enormous opening in the ground is essentially a wildlife refuge.
06:35This was confirmed in 2021.
06:38That's when biologists discovered two species in the Yunnan province that they previously
06:43thought had gone extinct.
06:45Who knows what other animal and plant species are still hiding in there.
06:50Exploring these underground cave systems can be quite dangerous.
06:54They are often home to venomous snakes and mosquitoes.
06:57Even descending into a sinkhole is perilous.
07:00The cliffs are steep and stones are often very sharp.
07:04That's why the exploration of sinkholes in Asia is going slower than research would like.
07:10The sinkholes I've mentioned so far have all formed naturally.
07:14Erosion is the main process behind their creation.
07:17But the ground can also open because of human activity.
07:21Moving from a construction site to a leaking sewer pipe can cause the earth to give way.
07:27Sinkholes in urban areas pose a risk to infrastructure.
07:31One of the most famous examples of this happened in Japan in 2016.
07:36A busy street in downtown Fukuoka collapsed near the main train station.
07:40The sinkhole severed power lines and pipes that lay underground.
07:44Luckily, no one was injured.
07:47The diligent Japanese engineers repaired the damaged road section in just 48 hours.
07:53The biggest issue with sinkholes is that you never know when and where they are going to open.
07:59The best tool that geologists have for detecting underground cavities is Ground Penetrating Radar, GPR.
08:06It resembles a landmower.
08:08The operator goes up and down a troubled area to scan the ground underneath.
08:12The radar sends out impulses that detect any contrast between different materials.
08:18It feeds back this info in the form of a 2D or a 3D image.
08:23Once engineers detect a potential sinkhole, they use different techniques to stabilize
08:28the ground above it.
08:29The simplest method is called grouting.
08:32It involves filling the hole so it won't collapse.
08:35The most common materials are polyurethane foam and cement.
08:40The alternative is to lift a structure above the sinkhole.
08:43This technique is called underpinning.
08:46Workers drive steel rods into the load-bearing deeper layer of soil.
08:51This is the same construction method engineers use to erect stilt houses above the waterline.
08:57That's it for today.
09:01So hey, if you pacified your curiosity, then give the video a like and share it with your
09:05friends.
09:06And if you want more, just click on these videos and stay on the Bright Side!
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