The eruption of the Hunga Tonga Hunga Ha’apai volcano in the South Pacific last week was brief, but extremely powerful.
A mushroom cloud of gasses and ash rose nearly 20 miles into the atmosphere. The shockwave created by the massive explosion traveled around the world twice and was reportedly heard in Alaska, about 5,000 miles away. The blast triggered tsunami warnings across the Pacific Ocean.
The eruption only lasted about 10 minutes but likely triggered some longer introspection for residents of the Pacific Northwest, which is dotted with volcanoes, both active and dormant, onshore and off. While the northwest Pacific is home to one of the world’s most active undersea volcanoes, known as the Axial Seamount, there is little threat of a cataclysmic eruption like the one in Tonga.
“There’s no real risk,” said Bill Chadwick, an Oregon State University researcher who has been studying volcanology in the Pacific Northwest for the past 30 years. “It’s pretty far offshore, and it’s in pretty deep water.”
That was far from the case last weekend in Tonga.
The volcano sat at a depth of just 650 feet, optimal for creating a large explosion, Shane Cronin, a volcanology professor at the University of Auckland, told The Associated Press.
When the pressure of building magma and gasses grew too great, the cone of the Tonga volcano ruptured and seawater flooded in and met with molten rock. The crack allowed the pressurized gasses to expand rapidly, Cronin said, and the water above vaporized in a flash, steam augmenting the already-towering mushroom cloud.
This satellite image taken by Himawari-8, a Japanese weather satellite, and released by the agency, shows an undersea volcano eruption at the Pacific nation of Tonga Saturday, Jan. 15, 2022. An undersea volcano erupted in spectacular fashion near the Pacific nation of Tonga on Saturday, sending large waves crashing across the shore and people rushing to higher ground. (Japan Meteorology Agency via AP)AP
At least three people are confirmed to have died in Tonga, which is about 50 miles south of the eruption site, and the ensuing tsunami killed two people and caused an oil spill in Peru. Still, given the size of the eruption, it’s relatively shallow depth and its proximity to Tonga, experts have said the damage was surprisingly limited.
By contrast, the top of the Axial Seamount, which rises to just over 3,600 feet tall about 300 miles west of Cannon Beach, sits under nearly a mile of ocean water. You don’t have to look far back in the history books to find an eruption, either. The seamount has erupted several times over the past couple decades, most recently in 2015.
The only way to actually detect an eruption of the seamount, though, is with technical instruments. The volcano is so deep underwater, Chadwick said, that even if you were directly over it during an eruption, there would be no detectable change at the surface, not even a bubble.
“The deep ocean is very secretive,” he told The Oregonian/OregonLive. “To detect an eruption at Axial, if you were over it in a ship, you’d have to lower some instruments down over the side. Either something to measure temperature or chemical anomalies from the hydrothermal plumes being produced.”
The seamount sits over a “hot spot” in the Earth’s crust. As the tectonic plate moves over the hot spot, the ground is forced up. The result has been a chain of seamounts forming, much like the Hawaiian islands. Axial is the youngest and only active member of the chain.
What it lacks in pyrotechnics, the Axial Seamount more than makes up for in research opportunities.
The seamount is home to an array of sensors that measure geophysical, chemical and biological changes on the seafloor and in the water as well as cameras that capture images of the volcano, all sent back to shore in real time via undersea cable.
“It’s totally unique in the world,” Chadwick said. “It’s one of the most active submarine volcanoes that we know of, and it’s the best monitored in the world.”
The volcano has provided data that allowed researchers to predict its most recent eruption seven months in advance, which could hold the key to forecasting eruptions on land, according to Chadwick.
“During its eruptions, Axial’s seafloor drops suddenly by about 8 feet, and then over the next several years it gradually rises back up,” he said. “When it re-inflates to a certain level, the volcano is almost ready to erupt again.”
The seamount essentially acts like a balloon, Chadwick said, except instead of filling with air, the chamber fills with molten rock.
Early predictions called for another eruption sometime in the first half of this decade, but the rate of magma filling the seamount has slowed recently, Chadwick said. In his most recent paper, published in December, he and a team of researchers pushed back their forecast for an eruption to the latter half of the 2020s.
The next time it does go off, Chadwick and dozens of researchers will be poring over the data, looking for clues they can apply elsewhere so that those who live near volcanoes that pose very real threats, like the people of Tonga, can be better prepared next time a more dangerous eruption occurs.
-- Kale Williams; kwilliams@oregonian.com; 503-294-4048; @sfkale