When most people think of Yellowstone, they picture stunning landscapes, roaming bison, and tranquil nature. But beneath the surface lies a deadly secret: Yellowstone is built atop one of the world’s largest and most dangerous supervolcanoes—a threat that could erupt with devastating consequences.

In 1965, NASA launched a mission to map Earth’s surface from space, using advanced cameras mounted on satellites. To ensure their images were accurate, they created a control set of ground pictures in Yellowstone, led by geologist Bob Christiansen.

Yellowstone’s unique geology, with its geysers and hot springs, made it the perfect test site. Christiansen also collected rock samples for carbon dating, and what he found was startling: most of Yellowstone’s rock was rhyolite, a volcanic stone formed only by lava flows or massive explosions. Yet, no active volcanoes were visible.

The data revealed that Yellowstone’s landscape was shaped by a series of colossal eruptions over the past two million years. Christiansen initially believed these features came from an ancient chain of volcanoes.

However, when NASA’s infrared satellite mapping was completed in 1972, the images told a different story. The park’s features weren’t the result of multiple volcanoes, but of a single, enormous supervolcano—one of only about twenty known on Earth.

The largest eruption, two million years ago, ejected 600 cubic miles of lava and rock, an explosion 2,500 times more powerful than the infamous Mount St. Helens eruption. Even more alarming, Yellowstone’s supervolcano isn’t entirely dormant. Lava still flows beneath the park, and a 2022 study published in Science revealed that its underground magma chambers are rapidly filling.

Combined with the fact that Yellowstone experiences over 3,000 earthquakes per year, scientists warn it may be preparing to erupt again. If it does, the resulting debris could block out the sun across the western United States for decades, causing famine and economic collapse.

But not all threats erupt from beneath the earth. In northwest Siberia, another deadly danger emerged, this time from the melting permafrost. In a small town, a farmer discovered a dead reindeer—ordinary enough, until hundreds more began dying. Soon, villagers fell ill with high fevers and painful sores, and one child tragically died. Doctors were stumped until tests revealed the culprit: Bacillus anthracis, better known as anthrax.

Anthrax spores exist naturally in soil worldwide. When animals graze, they can inhale these spores and become infected. After death, decomposing bodies release even more spores into the earth, where they can remain dormant for decades. In the early 1900s, Siberia suffered devastating anthrax outbreaks, killing over a million reindeer. Many carcasses were frozen in permafrost, preserving both the animals and the deadly bacteria.

Starting in 2011, Siberia experienced five unusually warm summers. The extreme heat melted the permafrost, exposing dormant anthrax spores and triggering a new outbreak. Officials responded by burning thousands of carcasses and vaccinating tens of thousands of reindeer, eventually halting the epidemic. Yet, researchers warn that many more ancient pathogens remain locked in Arctic ice. As global temperatures rise and permafrost continues to melt, humans and animals could face diseases unseen for centuries—a Pandora’s box of ancient threats waiting to be unleashed.

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Both Yellowstone’s supervolcano and Siberia’s melting permafrost remind us that the earth’s greatest dangers are often buried just beneath our feet, waiting for the right moment to change history.