Things are heating up hundreds of miles off the coast of Oregon, where a large undersea volcano is showing signs of impending eruption, scientists say.

The volcano, known as Axial Seamount, is located nearly 1 mile (1.4 kilometres) underwater on a geological hot spot, where searing gushes of molten rock rise from Earth’s mantle and into the crust.

Hotspot volcanoes are common on the seafloor.

But Axial Seamount also happens to be located on the Juan de Fuca Ridge — an area where two massive tectonic plates (the Pacific and the Juan de Fuca plates) are constantly spreading apart, causing a steady buildup of pressure beneath the planet’s surface.

The frequency of earthquakes has recently picked up dramatically as the volcano inflates with increasingly more magma, signalling an eruption could be near, according to researchers at the National Science Foundation’s Ocean Observatories Initiative Regional Cabled Array, a facility operated by the University of Washington that monitors the activity of Axial Seamount.

“At the moment, there are a couple hundred earthquakes a day, but that’s still a lot less than we saw before the previous eruption,” said William Wilcock, a marine geophysicist and professor at the University of Washington School of Oceanography who studies the volcano.

“I would say it was going to erupt sometime later (this year) or early 2026, but it could be tomorrow, because it’s completely unpredictable,” he said.

What happens during an eruption?

During the volcano’s last eruption in April 2015, the team observed about 10,000 small-scale earthquakes in a 24-hour-period, and the same can be expected for the next one, Wilcock said.

Magma — molten rock beneath Earth’s surface — oozed out of Axial Seamount for a month and trailed about 25 miles (40 kilometres) across the seafloor, he added.

The magma chamber at the heart of the volcano has also collapsed several times in the past, creating a large crater called a caldera.

There, sea life thrives off the mineral-rich gases that exit through hydrothermal vents, which are like underwater hot springs.

Streams of hot fluid containing billions of microbes and clumps of waste billow up from cracks in the caldera’s surface, creating white plumes called “snowblowers.”

During previous eruptions, the small plants and animals living on the hydrothermal vents were scorched by lava flows, but just three months later, their ecosystem was back and flourishing again, said Debbie Kelley, director of the Regional Cabled Array.

“I think it’s one of the biggest discoveries we’ve made,” said Kelley, a professor of marine geology and geophysics at the University of Washington, in a statement.

“Life thrives in these inhospitable environments, and volcanoes are probably one of the major sources of life in our oceans.”

While neighbouring marine life such as fish, whales and octopuses may feel the heat and rumble of seismic shifting, they are unlikely to be harmed. And people on land probably won’t notice the eruption at all, Kelley told CNN.

“It’s not a very explosive event. You won’t see the ash clouds above water, anything like that,” she said.

“It’s like if you put a mile of seawater on top of Kilauea … you may see some fountaining, but that’s it.”

In fact, most of the planet’s volcanic activity takes place within underwater spreading centres such as the Juan de Fuca Ridge, which experiences multiple, small volcanic eruptions each day, Kelley said.

“The magma’s pretty close to the surface. It’s about a mile beneath the surface, which is very shallow compared with a lot of land volcanoes, where it may be 8 miles (12.9 kilometers) deep,” Kelley said, adding that the viscosity, or thickness, of the magma can affect how much pressure builds up in the magma chamber.

Like a thick tomato sauce cooking on the stove, air bubbles within high-viscosity magma rupture more dramatically than Axial Seamount’s thinner, runnier magma.

Luckily, the relative mildness of Axial Seamount makes it perfect for close human observation.

The next time the volcano erupts, the observatory even plans to publicly livestream the event, which has never been done before, Kelley said.

Observing an undersea volcanic eruption is no easy task. Scientists only directly witnessed one in action for the first time on April 29.

In the Pacific Ocean, about 1,300 miles (2,092 kilometres) west of Costa Rica, researchers partnering with the Woods Hole Oceanographic Institution, or WHOI, were on a routine submersible dive to collect data on the East Pacific Rise when they noticed the once-vibrant Tica vents were no longer teeming with sea life.

Instead, the team found a charred “tubeworm barbeque,” as WHOI Emeritus Research Scholar Dan Fornari put it.

Flashes of orange lava leaked through the seafloor before hardening in the freezing water, indicating an eruption was taking place.

“It’s quite a significant development,” Fornari said.

“It’s a very understudied environment, because it’s hard to reach and because we have to use clever technology to understand it. … At the heart of it, we are watching (the) ways in which this planet gets built, gets constructed by volcanism on the seafloor.”