Sleeping Giant

Each year, millions of visitors flock to Yellowstone National Park to marvel at its natural wonders. Inside the park, which spans parts of Wyoming, Idaho, and Montana, geysers spray boiling water high into the air next to multicolored hot springs. But Yellowstone’s most unique feature isn’t something people can see—it’s buried 8 kilometers (5 miles) underground.

Gigantic chambers of magma lie hidden beneath Yellowstone. This mixture of melted rock, crystals, and dissolved gases churns underground, providing the heat that fuels Yellowstone’s geysers and hot springs. But the magma chambers aren’t just furnaces for the park’s natural wonders. They’re also the heart of a supervolcano—an extremely large volcano that, if it were to erupt, could change the face of Earth.

Scientists once believed supervolcanoes slowly built up from dormancy—a period of relative inactivity—to an eruption over thousands of years. But a recent study suggests that the time between dormancy and a supervolcano blowing its top could instead be decades. Today, researchers are working to learn more about what’s going on inside the Yellowstone supervolcano to better understand when and how it could erupt.

Each year, millions of visitors flock to Yellowstone National Park to see its natural wonders. The park covers parts of Wyoming, Idaho, and Montana. There, geysers spray boiling water high into the air. Steam rises from hot springs of many colors. But Yellowstone’s most unique feature isn’t something people can see. It’s buried 8 kilometers (5 miles) underground.

Huge chambers of magma are hidden under Yellowstone. This mixture of melted rock, crystals, and dissolved gases boils underground. It provides the heat that powers Yellowstone’s geysers and hot springs. But the magma chambers aren’t just furnaces for the park’s natural wonders. They’re also the heart of an extremely large volcano called a supervolcano. If a supervolcano were to erupt, it could change the face of Earth.

Volcanoes that aren’t very active are in a period called dormancy. They have to slowly build up to an eruption. Scientists used to think this took thousands of years for supervolcanoes. But a recent study suggests that a supervolcano could go from dormancy to blowing its top in decades. Researchers are working to learn more about what’s going on inside the Yellowstone supervolcano. They hope to better understand when and how it could erupt.

Yellowstone is just one of about 20 supervolcanoes scientists have found spread around the globe. “They’re not the kind of volcano you see in a picture book,” says Michael Poland, the scientist-in-charge at the Yellowstone Volcano Observatory. “There are no pointy mountains—they’re all underground. But they’re really, preposterously big.”

Yellowstone formed over a hot spot, a column of hot rock and magma rising up from deep within Earth (see A Really Big Volcano). Like a giant blowtorch, this fiery plume heats the rocks under Yellowstone until they melt. The resulting buildup of magma pushes up on Earth’s crust, or outermost layer.

Yellowstone isn’t the only supervolcano. Scientists have found about 20 around the world. “They’re not the kind of volcano you see in a picture book,” says Michael Poland. He’s the scientist-in-charge at the Yellowstone Volcano Observatory. “There are no pointy mountains—they’re all underground. But they’re really, preposterously big.”

Yellowstone formed over a hot spot. That’s a column of hot magma rising from deep within Earth (see A Really Big Volcano). This fiery column acts like a giant blowtorch. It heats the rocks under Yellowstone until they melt. This causes a buildup of magma that pushes up on Earth’s crust, or outermost layer.

A supervolcano’s magma chambers can remain dormant for millions of years, says Poland. But the hot spot can suddenly begin pumping large amounts of magma into the system, causing the pressure inside the chambers to increase. And when the pressure becomes too high for the crust to contain, the supervolcano can erupt.

No one can predict the timing or size of the next supereruption at Yellowstone, but it’s possible that the fallout could cover much of the U.S. in a layer of ash several inches to several feet deep (see Blast Zone). Volcanic particles spewed into the atmosphere could temporarily block sunlight and cool Earth by several degrees for as long as a decade. The resulting volcanic winter could make it hard to grow food—leading to food shortages and mass migrations of people and animals.

A supervolcano’s magma chambers can stay stable for millions of years, says Poland. But the hot spot can start pumping large amounts of magma into the system. This causes the pressure inside the chambers to rise. Finally, the pressure becomes too high for the crust to hold. That’s when the supervolcano can erupt.

No one can tell when or how big the next supereruption at Yellowstone will be. But the fallout could cover much of the U.S. in a layer of ash several inches to several feet deep (see Blast Zone). Volcanic particles that pour into the air could block sunlight for a time. That could cool Earth by several degrees for up to a decade. This volcanic winter might make it hard to grow food, leading to food shortages and mass migrations of people and animals.

The researchers closely examined the crystals’ layers with a scanning electron microscope. This instrument uses beams of negatively charged particles called electrons to scan an object’s surface to determine its composition and structure. The outermost layer of the crystals formed during the time it took for magma to begin building beneath the supervolcano until its eruption. Shamloo and her colleagues expected to see that this layer grew over hundreds of thousands of years. Instead, it appeared that the layer had formed in a matter of decades. The scientists concluded that the supervolcano went from dormancy to eruption much more quickly than originally thought.

The researchers studied the crystals’ layers with a scanning electron microscope. This tool uses beams of negatively charged particles called electrons. The beams scan an object’s surface to reveal its makeup and form. The crystals’ outer layer formed from the time the magma started building under the supervolcano until its eruption. Shamloo and her co-workers expected to see that this layer grew over hundreds of thousands of years. Instead, it looked like the layer had formed over decades. The scientists concluded that the supervolcano went from dormancy to eruption much faster than they’d thought.

Yellowstone’s supervolcano may sound like a disaster movie. But Poland says not to worry. His team keeps a constant eye out for signs that could indicate Yellowstone might be ready to blow.

To do so, Poland and his team use a variety of instruments to infer, or make educated guesses about, what’s happening inside the volcano’s magma chambers below. Devices called seismographs measure energy waves caused by earthquakes. And GPS sensors placed around the park give Poland’s team information about ground deformation—how volcanic activity causes the land to shift.

Yellowstone’s supervolcano may sound like a disaster movie. But Poland says not to worry. His team keeps a constant eye on the volcano. They look for signs that Yellowstone might be ready to blow.

Poland and his team try to figure out what’s happening inside the volcano’s magma chambers. Different instruments help them infer, or make educated guesses about, underground activity. Instruments called seismographs measure energy waves caused by earthquakes. And GPS sensors are placed around the park. They give information about ground deformation. That’s the way volcanic activity shifts the land. 

Earthquakes and ground movement are common in such a geologically active area. It would take drastic changes for Poland to become concerned. Even if Yellowstone erupted, he says, it wouldn’t be world-ending.

“I get letters and emails from students who are scared about supervolcanoes,” says Poland. “But let me be clear—a supereruption is very rare, and there’s no sign of it happening soon. A supereruption would be devastating to the region, but we would survive.”

This area is very active geologically. Earthquakes and ground movement are common. It would take great changes for Poland to get worried. He says that even if Yellowstone erupted, it wouldn’t be world-ending.

“I get letters and emails from students who are scared about supervolcanoes,” says Poland. “But let me be clear—a supereruption is very rare, and there’s no sign of it happening soon. A supereruption would be devastating to the region, but we would survive.”