When Was the Last Time Yellowstone Supervolcano Erupted?

© George Rose/Getty Steam vents and hot springs in the Norris Basin are viewed on September 23, 2022, in Yellowstone National Park, Wyoming. Sitting atop an active volcanic caldera, Yellowstone, America's first National Park celebrating its 150th Anniversary, is home to more geological hydrothermal features (geysers, mud pots, hot springs, fumaroles) than are found in the rest of the world combined.

In Yellowstone National Park, in the northwest corner of Wyoming, lies the Yellowstone caldera, one of the most famous supervolcanoes on Earth.

The supervolcano's last eruption was 631,000 years ago. Before then, it erupted 2.1 million and 1.3 million years ago. These eruptions were some of the largest known to man. If it were to erupt again, on the same scale as 631,000 years ago, a large part of the U.S. would be devastated.

But fortunately that does not appear likely to happen anytime soon.

Mike Poland, a scientist-in-charge at the U.S. Geological Survey's Yellowstone Volcano Observatory, told Newsweek that since the eruption 631,000 years ago there have been about 20 lava flow eruptions. These tend to happen in clusters of several eruptions in a single period, separated by long periods of quiet. The last cluster of eruptions occurred between 161,000 and 70,000 years ago.

"The most recent episode during which magma reached the surface at Yellowstone was 70,000 years ago. That was a lava flow," Poland said. "Lava flows are actually the most common form of activity at Yellowstone. It's a common misconception that Yellowstone only explodes."

What Kind of Volcano Is Yellowstone?

The Yellowstone volcano is a caldera, which is a basin formed when a magma chamber is emptied in an eruption. Yellowstone is known as a supervolcano, which is capable of producing ginormous eruptions, a thousand times more powerful than a normal one.

Unlike what happens with normal volcanoes, the effects of these eruptions are worldwide. A supervolcano eruption would destroy pretty much everything within a 40-mile radius. In the case of Yellowstone, pyroclastic flows would devastate the neighboring states of Montana and Idaho as well as Wyoming. Falling ash would also affect other areas of the country. The eruption would have long-term effects on the world's climate, potentially inciting droughts and floods.

The Yellowstone volcano can be viewed as a crater in the ground from the Washburn Hot Springs overlook, south of Dunraven Pass, in the national park. It is a collapsed volcano that has a magma chamber bubbling underground that is estimated to be 40 by 80 kilometers across, which is the same size as the caldera.

Is Yellowstone Volcano Active, Dormant or Extinct?

The Yellowstone volcano is active dormant, meaning it is not erupting now but could in the future.

The national park has many hydrothermal features, such as hot springs and geysers, which point to ongoing volcanic activity beneath the ground. There are also frequent earthquakes in the area.

But this does not mean that the Yellowstone volcano is getting ready to erupt.

"Because the area has lots of preexisting faults, as well as lots of groundwater, you get a lot of small earthquakes, typically about 2,000 per year on average," Poland said. "This may seem like a lot for a volcanic area, but this is background for Yellowstone."

He continued: "The ground also rises and falls regularly due to movement of gas, water and magma on occasion, also normal for Yellowstone. We've seen no indication of significant magma ascent or accumulation, and we're not particularly concerned about an eruption anytime soon.

"It's commonly suggested that the reactivation or cessation of a particular geyser, or of a thermal area, is an indication of Yellowstone heating up or something like that, but this is not true," Poland said. "The hydrothermal system is not directly connected to the magmatic system, and geyser activity is generally random and always dynamic. That's not a reliable indicator of any sort of volcanic unrest."

How Old Is The Yellowstone Volcano?

The Yellowstone caldera was created 631,000 years ago, with the last eruption. At that time, a hot spot within the Earth's mantle—underneath what is now Yellowstone National Park—pushed a huge plume of magma toward the Earth's surface. Cracks then formed in the ground, and when it could no longer sustain the pressure, an eruption occurred, creating the caldera we see today.

How Often Does Yellowstone Erupt?

There is an average of 725,000 years between eruptions at Yellowstone. In the meantime, other activity occurs, such as steam explosions.

"Some [steam explosions] can rarely be quite large, but small ones occur every few years in Yellowstone National Park, mostly in backcountry areas," Poland said.

He went on: "There is no magma involved in these events, so they are not volcanic eruptions, but if someone was standing nearby when one happened, it could cause injury. We can't say for certain [when it will next erupt], but there's no indication of it erupting anytime soon. We know from seismic imaging studies, which are like taking an MRI of the Earth, that the magma chamber is mostly solid."

This means the magma chamber has a long way to go before it gets close to another eruption.

"The most recent studies suggest that the magma chamber is only about 20 percent molten," Poland said. "So it's sort of stagnant. It would take a while for the reservoir to be remelted to a point where it could support a major eruption."

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