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In the Yunnan Province of southern China, there's a forest made of stone! Well, kind of. The famous "Stone Forest" is actually a natural collection of unusual rock formations, including pillars up to 30 meters tall! Its unique landscape has made the Stone Forest a popular attraction for tourists and scientists alike. Millions of people have made the trip to stare up at these rock pillars and wonder how the heck they ended up in such weird shapes. And for good reason! Stone Forest's rock formations have a lot to teach us about the geological past, and may even help us design better cities in the future.
[♪INTRO] If you want to visit the Stone Forest yourself, all you have to do is travel about 80 kilometers southeast of Kunming, the capital city of China's Yunnan Province. There, you'll find a massive maze of stone arches, pillars, tunnels, caverns, mushroom-like towers, and more. The geological smorgasbord covers an area of more than 350 square kilometers. These formations are such a world wonder that the Stone Forest- locally known as Shilin World Geopark- was named a UNESCO World Heritage Site in 2007. If you think a forest made of stone is cool, wait until I tell you it's not the only one!
Similar stone forests are found in several other Chinese provinces, as well as other countries like Malaysia, Indonesia, Australia, and Brazil. They all formed the same way, through a geological process known as karstification. The stone of Yunnan's Stone Forest is more than 260 million years old- that's older than the first dinosaurs! And at that time, Yunnan Province was covered by the Paleo-Tethys Sea. The rock layers consist of carbonate rocks like limestone and dolostone, which are formed from the remains of shallow ocean organisms.
Lots of sea creatures - especially tiny shelled plankton - build shells out of calcium carbonate. When they die, their bodies sink to the seafloor and add those minerals to layers of mud, which eventually solidify into stone. Fast forward a few million years, and tectonic activity forced these rock layers upward, exposing that ancient sedimentary stone to weathering forces like wind and water. And that's when the really exciting stuff happens. See, the thing about carbonate rocks is that they are easily dissolved by rain and streams. As water flows over the stone, it corrodes the rock and carries away little bits of it.
Over long time periods, those little sections of dissolving rock develop into crevices, caverns, and a complex assortment of shapes known as a karst landscape. Karst landscapes are known all over the world. They happen anywhere there's lots of limestone exposed to the surface. They can feature deep caves, dangerous sinkholes, stone towers, and more. But no place on Earth has a karst landscape as complex as Shilin Stone Forest. This one area includes nearly every known type of karst formation. It's like the Disney World of karst.
The shape of each specific rock formation is a record of all its exposure to water and its natural points of weakness. Over those many millions of years, as tectonic forces acted upon these rocks, they developed cracks and fissures, which then became the areas where water tended to collect and gouge through the stone. Clusters of stone pillars used to be solid hills. But as water carved down and down along natural crevices, it split the hill into towering segments. In some cases, the rock had more cracks in its lower layers, which caused the base to dissolve away more quickly, leaving narrow pillars with bulbous, mushroom-like tops.
A close look at the local rock formations reveals tinier details, like little channels and grooves etched by rainwater. And to this day, the shape of the Stone Forest continues to change. Some researchers estimate that the pillars are growing! This is because the erosion of the soil at ground level is faster than the erosion of the stones themselves. So the ground level and the top of the pillars are growing farther and farther apart. Thanks to a wet and humid climate, and a vast array of slightly damaged carbonate rocks, Stone Forest is one of the best places in the world for scientists to study the interaction between stone and water.
Those scientists need funding, and we do, too. So here's a short ad. Since you watch SciShow, I know you're the kind of person who loves learning outside of a classroom. And that's what makes Brilliant so great too. Brilliant is an online learning platform made for everyone from age 10 to 110. Those courses are crafted by world-class teachers from MIT, Harvard, and Stanford, and they're esigned to build your confidence in coding. Take their course on Algorithmic Thinking for example. In that course, you get to solve over 200 problems. It's far from falling asleep in a lecture hall! To learn for free on Brilliant for a full 30 days,
go to brilliant.org/scishow, scan the QR code onscreen, or click on the link in the description. Brilliant's also given our viewers 20% off an annual Premium subscription, which gives you unlimited daily access to everything on Brilliant. Besides just looking cool, there are even fossils within the stone pillars! These include the shells of molluscs, gastropods, and lots of tiny plankton and algae from the ancient ocean that once covered this region. And this karstification process has been going on for hundreds of millions of years! At Stone Forest, the beautiful rock formations are exposed at the surface. But at some nearby locations, rocks of the same age are buried beneath ash and lava rocks from ancient volcanic eruptions.
When geologists examined these volcanic deposits, they found the shape of caverns, sinkholes, and giant stone pillars underneath the lava rocks! These were ancient stone forests that became completely buried by volcanic eruptions, more than 250 million years ago! But there's more to these giant rocky pillars than lessons about the distant past. These stone formations might hold some clues to building better cities in the future. That's because Stone Forest has its own climate.
See, all that exposed rock absorbs lots of heat from the sun, just like a concrete wall on a hot day. But those tall pillars also create pockets of cool shade. Research has found that, compared to the surrounding landscape, Stone Forest experiences a higher average daily temperature, but less dramatic temperature fluctuation, and highest daily temperature peaks occur later in the day. I bet you've already figured out an analogous landscape full of tall stony pillars: cities full of skyscrapers. Those peculiar climate patterns of Stone Forest are surprisingly similar to what has been observed in cities.
But cities also have a lot of other climate-altering effects going on, like air pollution and car exhaust, which makes it tough for scientists to figure out how much of the temperature changes can be attributed just to the shapes of the buildings. But Stone Forest has skyscraper-like shapes without any of those other confounding factors! So researchers are hopeful that studying this natural landscape might help us better understand the ways that cities shape local temperatures, and maybe even guide us in building more ecologically-friendly cities in the future! This incredible landscape is also in danger, though. Human activity in the area has disturbed the ecosystem of plants and animals living around the rock formations.
Karst ecosystems are especially sensitive to external disturbances. Some research has found that Stone Forest has been experiencing an expansion of barren areas and a decrease in forested areas. Like the actual, living forest /within/ the Stone Forest park. So in addition to studying the landscape, scientists are working on conservation plans to preserve it, to keep this extraordinary natural wonder rock solid for as long as we can. [♪OUTRO]
