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.

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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]