Underwater volcanoes might be out of sight and, for many, out of mind. But recent warnings from scientists about potential imminent eruptions have led some to take the threat more seriously.
One such warning involves Axial Seamount, located about 300 miles off the coast of Oregon, USA. Experts say the underwater volcano is heating up, showing signs that it may erupt sometime within the next year.
In Greece, recent earthquakes near the island of Santorini have also prompted scientists to inspect the island’s large volcanic caldera and the nearby underwater Kolumbo volcano. While neither is expected to erupt imminently, scientists believe it's only a matter of time.
Why Should We Pay Attention to Underwater Volcanoes?
Deep Beneath the Ocean
Volcanoes are vents in the Earth’s crust that release hot ash, gases, and molten rock—known as magma.
People often imagine towering volcanoes like Mount Vesuvius or Mount Etna, spewing glowing lava. However, experts estimate that about two-thirds of Earth’s volcanoes lie beneath the ocean surface.
These hidden seafloor volcanoes—sometimes thousands of meters deep—can form new islands and create extreme ecosystems that may host unknown species.
Just like volcanoes on land, underwater volcanoes can trigger earthquakes and tsunamis, occasionally causing widespread devastation.
In 2022, the Hunga Tonga-Hunga Ha'apai eruption in Tonga led to a Pacific-wide tsunami. Waves reached Australia, New Zealand, Japan, and even the west coasts of North and South America.
The eruption killed three people, destroyed hundreds of homes, and severed Tonga’s global internet connection for five weeks by cutting the undersea cable.
Where Are Underwater Volcanoes Found?
Most underwater volcanoes are located where tectonic plates meet—either pulling apart or sliding past one another. This movement allows magma to rise from deep within Earth’s crust.
Tectonic plates cover the entire surface of our planet, meaning underwater volcanoes are spread across the globe, from the Atlantic and Pacific Oceans to the Mediterranean Sea.
Sometimes, hot spots—plumes of heat from deep within Earth—can form volcanoes in the middle of tectonic plates as well.
Different Types of Eruptions
According to Isobel Yeo, a marine volcanologist at the UK’s National Oceanography Centre (NOC), the interaction between magma and water makes underwater eruptions behave differently from those on land.
She explains: “Imagine pouring water into a hot pan—it instantly turns into steam. That’s exactly what happens in shallow marine volcano systems.”
In deeper locations, where the water pressure is much higher, such explosive reactions are less likely. Magma still escapes, but cools quickly under pressure.
The amount of gas in the water also determines how violent an eruption might be—the more gas, the more explosive the eruption.
How Often Do Underwater Volcanoes Erupt?
Yeo notes that estimating the number and eruption frequency of underwater volcanoes is extremely difficult because most are not regularly monitored.
Monitoring is costly, requiring advanced technology, submarines, ships, and remote access to hostile environments.
Some scientists estimate there may be thousands of underwater volcanoes, while others suggest the number could be as high as one million.
Most researchers agree that underwater volcanoes erupt more frequently than those on land, which makes sense since about 70% of Earth’s surface is underwater.
According to Deborah Kelley, a marine geologist at the University of Washington, only a few places on Earth have precise data about underwater volcano systems.
Volcanic Islands Born from the Sea
Many islands were formed by volcanic activity. For instance:
The Hawaiian Islands are a volcanic chain that likely began forming about 70 million years ago.
Santorini in the Aegean Sea formed after a massive eruption around 1630 BCE, according to NOAA.
Iceland is another example of a landmass created through sustained volcanic activity.
Yeo notes that black sand beaches are often a sign of volcanic origin.
Some volcanic eruptions even create new land. In 2023, a submarine eruption off the coast of Iwo Jima, Japan, created a brand new island.
However, some of these islands may erode and disappear back under the ocean over time.
Yeo says: “We’re likely to see more new islands forming, but also some vanishing.”
More Than Just Lava
Kelley stresses the ecological importance of monitoring submarine volcanoes.
“These volcanoes are like oases on the ocean floor, rich with incredible life forms,” she explains. “There’s so much biological activity that you can’t even see the rocks.”
Better understanding of these ecosystems is essential for responsible decisions about activities like deep-sea mining.
She adds: “We need to know what’s living down there, how it affects the broader ocean, and whether it can survive long-term before we disturb it.”
Should We Be Worried?
Yeo says all volcanoes—land or sea—pose risks.
“I don’t think we should worry more about underwater volcanoes than other kinds,” she says. “But we do need to monitor them better—which we currently don’t.”
In April, tourists and locals were evacuated due to a volcanic eruption in Iceland.
Yeo believes the same kind of preparedness should apply to submarine eruptions. They carry their own dangers—not just from eruptions, but from the risk of underwater landslides triggering tsunamis.
The Case of Axial Seamount
Kelley has helped monitor Axial Seamount, whose base lies nearly 2,600 meters beneath the Pacific Ocean.
The volcano is tracked using a 500-kilometer-long cable stretching from the coastline directly to the volcano.
Thanks to this system, scientists have noticed rising temperatures and signs of inflation that exceed previous pre-eruption levels.
This could indicate that an eruption may occur within the next year, although due to ocean pressure, it’s unlikely that people on land would notice.
Kelley believes advancing technologies will allow for better monitoring in the future.
She concludes: “This is an incredibly important part of our planet—and we absolutely need to learn more about it.”
