10 Explosive Facts You Probably Don’t Know About Volcanoes

Volcanoes are one of Earth’s most dramatic geological features. Although they can go thousands of years between eruptions, they have the power to vastly change the landscape when they do erupt. There are many world-famous volcanoes on the map—from Japan’s Mount Fuji to Italy’s Mount Vesuvius—but while most people have a basic knowledge of those peaks, there are plenty of explosive facts about volcanoes that aren’t as well known. Here are 10 such facts—from a volcano that spits out diamonds to one that is taller than Everest.

Related: 10 Surprising Ways Living on Mars Would Compare to Earth

10 People Can Sled Down Cerro Negro

On the west coast of Nicaragua stands Cerro Negro, the slopes of which are coated in black sand. The volcano last erupted in 1999, but it has been quiet ever since, and in those years, a booming industry has developed: volcano boarding. Anyone willing to trek for an hour up the slopes of the cone is treated not only to a scenic view from the top but also to a thrilling way to get down. Visitors are provided with orange jumpsuits and goggles and then hop onto what is essentially a sled.

Although sometimes described as volcano surfing, the vast majority of people descend while seated. “The descent is so steep that you get going very fast, and it’s pretty challenging to control the board,” says Javier Silva, a resident of Nicaragua. It takes less than a minute to reach the bottom, and people can reach speeds of up to 40 miles per hour (64 km/h). Being up close to a volcano is thrilling enough as it is, but volcano sledding takes it to another level.^[1]

9 Some Volcanoes Erupt Diamonds

Most volcanoes spit out magma, ash, and gas when they erupt, but there are a few rarer volcanoes that have ejected another material: diamonds. The precious gems form under extreme pressure, more than 93 miles (150 km) beneath Earth’s surface. It’s rare, but kimberlite eruptions are what bring diamonds to the surface.

Kimberlite volcanoes are roughly carrot-shaped—they can be hundreds of meters wide at the surface but are usually much narrower at depth in Earth’s mantle. These volcanoes formed where Earth’s crust is oldest, in places such as South Africa and Brazil. But there’s no point in hanging around these volcanoes hoping that diamonds will rain down on you. The last kimberlite eruption is thought to have occurred more than 25 million years ago.^[2]

8 Mauna Kea Is Taller Than Mount Everest

It’s well known that Mount Everest is the highest peak on Earth, stretching 29,032 feet (8,849 m) into the air. But Everest only holds the title of tallest mountain if the measurement is taken from sea level. When measured from base to summit, Everest is actually overshadowed by Mauna Kea, which comes in at a staggering 33,497 feet (10,210 m).

Hawaii’s Mauna Kea is a dormant volcano, and it’s not typically recognized as Earth’s highest peak because the large majority of its height is underwater. Only the top 13,802 feet (4,207 m) of Mauna Kea sits above the waves, meaning that it isn’t nearly as challenging to climb as many other peaks around the world. Although the volcano is currently considered dormant—last erupting roughly 4,500 years ago—it’s possible that the behemoth will one day awaken.^[3]

7 Mauna Loa Is Used to Train People for Life on Mars

Most people wouldn’t choose to live on an active volcano, but for those with hopes of one day traveling to Mars or the Moon, it’s a near-ideal training ground. The Hawaii Space Exploration Analog and Simulation (HI-SEAS) has been running since 2013 and involves six people at a time living in a small dome—for four months to a year—that sits 8,200 feet (2,500 m) high on the slopes of Hawaii’s Mauna Loa, Earth’s largest active volcano.

According to the HI-SEAS program, this “allows crews to perform high-fidelity geological and astrobiological field work and add to the realism of the mission simulation.” The simulation is designed to be as realistic as possible, so there’s a 20-minute delay in communication with anyone outside the dome, they use composting toilets, and when they go outside, they have to wear a spacesuit.

In addition to preparing people who might one day go into space, the simulation also provides researchers with important data. “This is about crew cohesion and performance,” explains Kim Binsted, the principal investigator of HI-SEAS. “What we’ve found is that there’s no magic bullet to prevent conflict—it’s how you deal with it and how you respond to it, not just as individuals but as a group.” ^[4]

6 Theres an Active Lava Lake in Antarctica

The coldest temperatures ever recorded occurred in Antarctica, with temperatures dropping to −137°F (−94°C) on the Eastern Antarctic Plateau. But being the coldest place on Earth hasn’t stopped the icy continent from also being home to a volcano with an active lava lake—a relatively rare feature that has only been found in a handful of volcanoes worldwide.

Mount Erebus’s caldera has contained a persistent lava lake since 1972. However, the remoteness of the location meant that for many years scientists didn’t know much about this volcano. That has changed in recent years, with researchers finding that Erebus is rich in carbon dioxide rather than water, as is found in many other volcanoes around the world. This allows its magma to rise closer to the surface. But there are still plenty of unanswered questions about what makes Erebus tick.^[5]

5 Mount Paektu’s Unusual Location

Mount Paektu is located on the border between North Korea and China, and it’s responsible for one of the world’s largest-ever eruptions. In 946 CE, the volcano spewed 45 megatons of sulfur into the atmosphere. For comparison, when Indonesia’s Mount Tambora erupted in 1815, 28 megatons of sulfur were released, which was enough to cool the planet down and cause a “year without a summer.” Although Paektu’s eruption didn’t result in climate change (the reasons for this are still being debated), it did form the 3-mile-wide (5 km) caldera at the top of the volcano.

Something that makes Mount Paektu’s power particularly unusual is its location. Volcanoes usually form where tectonic plates meet, but Paektu lies more than 600 miles (965 km) away from the Pacific Plate boundary. For a volcano, this means it’s essentially in the middle of nowhere. Why exactly that is isn’t clear, but there are hopes that Paektu’s recently awarded status as a UNESCO Global Geopark will open the door to researchers wanting to study the mountain.^[6]

4 Mount Unzen Was Once Used to Execute Christians

Mount Unzen is Japan’s most deadly volcano. Located on the island of Kyushu, at Japan’s southern tip, the volcano has killed thousands of people over the years. The worst disaster was in 1792, when an eruption triggered a landslide and tsunami that claimed the lives of roughly 15,000 people. But Unzen has also killed people in a rather more unique way, too. Throughout the 17th and 18th centuries, the volcano was used to execute Christians.

The Edo government was intolerant of Europeans coming to Japan and spreading Christianity. If a Christian was discovered—be they a European traveler or a Japanese local who converted—they were tortured and commanded to abandon their faith. If they still refused, they were thrown into Unzen’s volcanic hot springs. In addition to being boiling hot, the springs are also highly acidic, resulting in a very painful death.

Death by volcano stopped being used as a form of execution at the start of the 19th century, and the persecution of Christians officially ended in 1856.^[7]

3 Sharks Live in an Underwater Volcano

Although people tend to think of volcanoes on dry land, there are actually far more underwater, with an estimated one million volcanoes sprouting from the ocean floor. Kavachi, just off the coast of the Solomon Islands, is one of the more active underwater volcanoes, and it surprised scientists back in 2015 when it was discovered that sharks were living inside its crater.

A team led by ocean engineer Brennan Phillips dropped a camera into the crater—66 feet (20 m) below the ocean’s surface—and surprisingly found marine life somehow thriving in the hot, acidic, and ash-filled water. They expected to find only bacteria living in the crater but captured footage of large animals—including a silky shark, a scalloped hammerhead shark, and a sixgill stingray—swimming through the volcano’s plume.

“It brings up lots of questions,” Phillips explains. “Do they leave? Do they have some sort of sign that it’s about to erupt? Do they blow up sky-high in little bits?” The answers to these questions about the so-called “sharkano” are currently still a mystery, but hopefully in the coming years researchers will gain a better understanding of this strange and unexpected ecosystem.^[8]

2 Bright Blue Fire Burns on Kawah Ijen

It’s sometimes reported that Indonesia’s Kawah Ijen has blue lava, but that isn’t true. The electric blue glow is actually caused by hot sulfuric gases—reaching temperatures of up to 1,112°F (600°C)—leaking from cracks in the volcano and then bursting into flames when they hit the air. The confusion is understandable, though, because the gases often condense into liquid sulfur, which, in the words of photographer Olivier Grunewald, “continues to burn as it flows down the slopes, giving the feeling of lava flowing.”

The blue fire is constantly burning—and the flames can reach up to 16 feet (5 m) high—but it’s most visible at night, so visitors who want to see this otherworldly volcano usually hike it in the dark. The gases in the air are also toxic, so visitors need to wear a gas mask while on the volcano. In addition to the bright blue flames and rivers, the crater at the top of Kawah Ijen is also home to the world’s largest acid lake.^[9]

1 Ol Doinyo Lengai Has Black Lava

Although Kawah Ijen’s lava isn’t actually blue, Ol Doinyo Lengai really does spew black lava. Located in the north of Tanzania, it’s the only volcano in the world that erupts carbonatite lava. Most lava contains a lot of silica, which is what gives it its thick texture, but Ol Doinyo Lengai’s lava is light on silica and instead rich in sodium and calcium carbonate, which is why it’s black in color and fluid in texture.

As well as being an unusual color—which turns silvery white after cooling in the air on the surface—Ol Doinyo Lengai’s lava is also the coolest on Earth, melting at just 932°F (500°C) (lava usually melts at roughly double that temperature). Although it can be tricky to get samples of the lava because it bubbles away in vents at the bottom of a crater with sheer walls that stretch up 328 feet (100 m), its cooler temperature means that it can easily be scooped up with steel cups.

But black lava isn’t the only interesting thing about Ol Doinyo Lengai. The calcium-laced ash it emits adds minerals to the land surrounding it, allowing the Serengeti to flourish with animal and plant life. The volcano even helps drive the Great Wildebeest Migration; each year, more than one million wildebeest (which are often deficient in calcium) benefit from the Serengeti’s calcium-rich plants.^[10]