Huge undersea volcano off the West Coast may be getting ready to erupt

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A miles-wide volcano off Oregon’s coast could erupt “soon” say scientists who’ve been tracking it for decades.

The Axial Seamount is a massive undersea volcano that reaches more than 3,600 feet above the seabed, 300 miles offshore. It last erupted in 2015 but has a history of more than 50 different eruptions over the last 800 years.

The good news is that because the top of the volcano is still 4,500 feet below the ocean’s surface, it poses no danger to people.

“If you were in a boat right over the seamount you probably would never know it’s erupting, as there’s no effect on the ocean surface,” said Bill Chadwick, a volcanologist with Oregon State University who’s part of a team that’s studying the volcano. “Though if you lowered a hydrophone you might hear it because there’d be a lot of commotion going on.”

The volcano "is the most active in the Pacific Northwest" but little known by the public because even its tip is almost a mile under water.

But scientists know it well. An extensive series of instruments around the volcano indicate the magma reservoir as much as a mile below the volcano’s caldera has been refilling with magma since its last eruption, gradually inflating so that it's bulging upward.

“A year ago, Axial seemed to be taking a nap but now it’s waking up and we think it’s likely to erupt before the end of 2025,” said Chadwick.

It’s also been experiencing hundreds of small of earthquakes recently. On Monday alone, there were as many as 250 per hour, researchers at the University of Washington reported.

Both are signs of a coming eruption.

What will happen when Axial erupts?

The mechanics of an Axial eruption are much like those of volcanos in Hawaii and Iceland.

The volcano lies above a “hot spot” in Earth’s crust, where the Juan de Fuca tectonic plate meets the Pacific plate, and where magma is coming up through a plume from Earth’s mantle.

“The pressure inside the volcano is building,” Chadwick said. “Eventually, it becomes too great and a crack opens up and lava spews out of the fissure.”

On land, this is sometimes called a curtain of fire because it results in long, linear eruptions which can be “pretty spectacular,” he said.

Underwater, the lava cools more quickly than it would in the air, so instead it makes what’s known as pillow lava. These are bulbous pillows of lava that form enormous mounds that can overwhelm everything around them.

“In the 2015 eruption, they were 450 feet deep. For perspective, that’s two-thirds the height of the Space Needle in Seattle,” Chadwick said.

The eruptions can last between days and months, so the researchers hope they can get an unmanned submersible down to see what’s happening while the lava is still flowing.

“Nobody’s ever witnessed an eruption like that,” he said.

Not a danger, but an amazing research opportunity

The eruption couldn't trigger a tsunami or earthquakes on land, but it would expel enormous amounts of lava into the ocean. In 2015, Axial spewed out 5.5 billion cubic feet of lava.

Studying Axial is important because it’s a natural laboratory for volcanologists, allowing them to test theories and safely make predictions.

“Because this volcano is way offshore and it has no impact on people, we have the freedom to do that. With volcanos where people live, you don’t want to have false alarms,” said Chadwick, whose research is funded by the National Science Foundation.

Axial is the world’s most extensively studied undersea volcano because more than 660 miles of undersea cables crisscross it, sending a steady stream of real-time data about the area to scientists. The Regional Cabled Array includes more than 140 instruments that are constantly monitoring it.