9 stunning natural mysteries scientists can't fully explain

In New York's Chestnut Ridge Park, a flickering fire lends its name to the Eternal Flame Falls. Protected from the waterfall in a rocky alcove, it can burn on its own indefinitely, though it does sometimes go out.

It's an extremely rare phenomenon. There are fewer than 50 eternal flames around the world, geologist Giuseppe Etiope told National Geographic in 2024. Flammable natural gas, created when extremely high temperatures cook organic materials, seeps out from underground, constantly fueling the flame. Humans, forest fires, or lightning might set them alight.

What's unusual about the flame in New York is that its source, over 1,300 feet below the surface in the Rhinestreet Shale formation, is comparatively cool.

"The traditional hypothesis of how natural gas forms is, you have to heat to more than boiling water," researcher Arndt Schimmelmann told State Impact Pennsylvania in 2013. "But our rock here is not that hot and has never been that hot."

One of the researchers' theories was that minerals like iron or nickel could provide the flame's catalyst.

Ancient Greek philosopher Aristotle wrote, "Eels are derived from the so-called 'earth's guts' that grow spontaneously in mud and in humid ground."

Over 2,000 years later, scientists knew that wasn't true, but they still had no idea how eels reproduced. Danish biologist Johannes Schmidt traced migrating European eels to what he believed was their spawning location in the Sargasso Sea. Some travel over 3,000 miles to reach the region of the North Atlantic bounded by four currents.

That discovery was over 100 years ago, and scientists still have questions about how European eels travel, including how they navigate, their routes, and how quickly they swim.

Learning more about how these eels reproduce is critical because the number arriving in Europe has plummeted by 95% since the 1980s.

In 2022, scientists published a paper describing how they had tagged eels and confirmed that adults do migrate to the Sargasso Sea, possibly to spawn. Despite years of research, no one has found adult eels or eggs at the location, causing some to doubt it's the site of reproduction. Slippery as an eel, indeed.

Fly over Katmai National Monument in southwestern Alaska, and you'll see a lake that looks almost too perfect not to be human-made. It's over 1,600 feet across and more than 360 feet deep.

Melting snow and rain have filled in a crater, which formed sometime during or before the last ice age. In the 1960s and '70s, scientists studying the Savonoski Crater tried to find evidence of a meteoric impact. It does seem possible a meteor caused the deep, round hole.

However, receding glaciers likely took any remnants of the impact with them.

The crater could also be the result of a volcanic maar, which University of Alaska Fairbanks professor T. Neil Davis described as a "volcano that tried but failed" in a 1978 article on the mysterious Savonoski puzzle.

When a magma pipe hits a water table near the earth's surface, it erupts in an explosion of steam, forming a rock pit. The maar continues to spew smoke and ash before subsiding due to a lack of pressure.

In Josephine Tey's 1952 novel "The Singing Sands," a police inspector gets caught up in a murder investigation involving an enigmatic poem: "The beasts that talk, The streams that stand, The stones that walk, The singing sand…"

While the story is fiction, singing sand is very real, found in Indiana, Japan, Egypt, and California. Many, like those in Dunhuang, China, have become tourist attractions.

A low, vibrational hum emanates from sand spilling down dunes in these locations, sometimes loud enough to be heard 6 miles away. Certain conditions, like the size, shape, and silica content of the sand, have to align to produce the singing, according to NOAA.

Just why the frequencies of the tumbling sand sound like music is still a mystery, according to a 2012 study.

For decades, barren patches in the Namib Desert's arid grasslands have baffled scientists. Nicknamed "fairy circles," they stand out against the surrounding Southern Africa's green vegetation.

Some scientists have suggested that colonies of termites consume the plants and burrow in the soil, creating a ring that grows larger and larger. In a 2022 study, a group of researchers said they found no evidence of the insects in the circles they studied. Instead, they used sensors to monitor the plants' moisture uptake.

Their results suggested that ecohydrological feedback caused the bare circles. Essentially, these patches sacrificed having vegetation to divert more water to areas with grasses.

"These grasses end up in a circle because that's the most logical structure to maximize the water available to each individual plant," Stephan Getzin, an ecologist who led the study, told CNN in 2022.

Other researchers have posited that microbes could be a potential culprit for similar circles in Australia.

For years, curious visitors to Judge C. R. Magney State Park flung sticks, ping-pong balls, and colorful dyes into the Brule River to try and trace its flow. As it moves through the park, it spills out into several waterfalls, including the Devil's Kettle.

Part of the water cascades into a hole, and no one knew exactly where it went afterward. Some thought it might stream underground toward Canada or Lake Superior.

In 2017, hydrologists compared the amount of water above and below the falls, and it was almost identical. In other words, the water wasn't leaving at all but fed right back into the river at the base of the waterfall.

Scientists think they have a pretty good idea where the water reemerges, but they don't know for sure, hydrologist Jeff Green told Vice's "Science Solved It" podcast in 2018.

So where did all those ping-pong balls end up? The powerful, swirling currents would have smashed them to pieces, Green said.

When a 7.0 magnitude earthquake hit near Acapulco in 2021, people in Mexico City, hundreds of miles away, used their phone cameras to capture strange lights in the sky. Blue flashes lit up the sky like lightning.

Not all experts are convinced that earthquake lights exist, though they've been documented for centuries all over the world. Some scientists thought the flickers were from a damaged power grid or rainstorm, NPR reported.

Others are studying the phenomenon in hopes of using the lights, which sometimes occur prior to the earthquake, as a kind of early warning signal.

First, though, they would need to figure out why these flashes occur. A recent paper examined several possible causes of the lights, including escaping methane gas ignited by static electricity.

Off the coast of Western Australia is the vibrantly pink Lake Hillier. It looks surreal, as if someone dumped a massive amount of Pepto-Bismol into its super-salty waters.

Biologists have hypothesized that pigment-producing microbes are responsible for the lake's bright shade. In 2022, researchers published a study after looking at the water's microbiome. They found a number of bacteria, viruses, and algae. Some produced purple sulfur, and others were associated with a red-orange color. Together, they combined to make the pink color.

Researchers noted that other organisms could contribute, and further studies would have to be done.

That same year, there was a huge amount of rainfall, diluting the saltiness that's also a key factor in the color. Today, the lake is only tinged pink, but scientists think the brightness will return as more water evaporates, the Australian Broadcasting Corporation reported earlier this year.

People have used the Fosse Dionne for centuries, drinking in the turquoise waters without ever knowing where the rushing spring originated. In the 1700s, residents built a laundry around it to take advantage of the flow, which pours out over 82 gallons a second.

Located in Tonnerre, France, the spring feeds into a basin. Depending on the weather and other factors, its hue can change from green to blue to brown, the city's mayor told the BBC in 2019. Local legends said a mythical, snake-like basilisk once made the pit its home.

About a quarter mile of its course is known, but divers have lost their lives exploring the flooded cave along the route.

A professional diver, Pierre-Éric Deseigne, has reached unexplored areas of the cave but couldn't find the Fosse Dionne's origin, the BBC reported in 2019.