Hawaiian volcanoes suddenly go quiet, but scientists don’t know exactly why

But volcanologists don’t know whether there is a link between the end of the two eruptions, something that highlights the larger challenges the scientists face in analyzing and predicting volcanic activity. Mauna Loa is among the best understood and most closely watched volcanoes in the world because of its record of activity, with 34 eruptions since 1843, and yet significant questions remain about the factors influencing when it erupts and when it quiets.

That uncertainty extends to other hazardous volcanoes as well, prompting volcanologists to suggest that observations of the Mauna Loa eruption could help inform predictions of eruptions elsewhere.

There had been signs since September that Mauna Loa was primed for its first eruption in 38 years. It finally happened in late November. And volcanologists had been observing signals of diminishing activity at Kilauea in recent weeks. But it was otherwise challenging to pinpoint the timing of activity at either volcano.

“We’re getting better at forecasting the onset of eruptions because we have so much more data now,” said Einat Lev, an associate research professor at Columbia University’s Lamont-Doherty Earth Observatory. “We’re not making that much progress on predicting the end.”

Hon said about 200 million to 250 million cubic meters of lava flowed from Mauna Loa, which means “long mountain” in Hawaiian, over 12 days, a larger-than-usual amount of lava flow that reflects the abnormally long period since its last eruption.

While the lava flow crossed a road leading to a key observatory used to measure atmospheric carbon dioxide concentrations, it did not otherwise cause any damage. The lava flow stopped more than a mile and a half from the Daniel K. Inouye Highway, a busy road that serves as a shortcut between communities on the eastern and western coasts of the Big Island.

Talmadge Magno, the civil defense administrator for Hawaii County, called it “the best situation we could have asked for from Mauna Loa.”

Mauna Loa’s eruption was on par with the length of similar eruptions in the past, Hon said. Volcanologists had predicted that the eruption might last a few weeks, though they stressed that they could not predict its ending with much confidence.

Kilauea was the site of a significant eruption in 2018, which destroyed hundreds of homes in the Puna district of eastern Hawaii and caused a massive collapse in the volcano’s caldera. A smaller eruption began at the volcano in September 2021 and had continued through Mauna Loa’s eruption, which began Nov. 27.

But volcanologists believe the latest Kilauea eruption stopped sometime between Dec. 6 and Dec. 9, after a period of declining seismic activity within the volcano that had been observed since early November, Hon said.

The question of whether and how the volcanoes may be connected remains “controversial,” said Diana Roman, a volcanologist at the Carnegie Institute.

“Do they take turns? Are they both driven by some independent other part of the system that somehow turns one off and turns one on? We don’t know,” Roman said. “There are intriguing hints that perhaps they don’t act independently of each other.”

Hon said researchers will dig into observations of both volcanoes over the next year to find what they can learn about any relationship between them. Both are shield volcanoes, named for their wide and gradually sloping profile, and are fueled by a hot spot, or an area in the middle of a tectonic plate where Earth’s mantle has an outlet to the planet’s surface.

“Kilauea may have been diminishing on its own,” Hon said, adding that Mauna Loa’s eruption “may have caused enough physical changes to stop it, or it may have been headed to stop on its own.”

Meanwhile, volcanologists will also be studying observations of the volcanoes to better understand signals that might help them predict eruptions elsewhere, such as Mount Rainier near Seattle. Lava has not flowed from the stratovolcano in a millennium, and it has been 500 years since a lahar — a damaging wave of mud and debris — swept down its slopes.

Elizabeth Westby, a geologist at the Cascades Volcano Observatory, said that staff at that institution have been involved in observing Mauna Loa’s eruption, and that the experiences and lessons could pay dividends the next time volcanic activity occurs in the Pacific Northwest.

“It keeps us on our toes,” Westby said. “It’s good training.”

Scientists have evidence to believe Mount Rainier would provide ample warning of eruption through millimeter-scale bulging to its surface and spates of earthquakes as magma makes its way toward the surface. There are 20 monitoring stations on and around the volcano to detect those signals, Westby said.

But in volcanology unlike with, say, weather forecasting, there isn’t enough data available to model specific, high-confidence predictions of when eruptions will occur and how severe they might be. There are research efforts underway and in planning to improve eruption forecasting by increasing volcano monitoring in places like the Chilean Andes, scientists said.

But for now, it’s hard to say with certainty that volcanoes like Rainier will provide signals long before eruption, as Mauna Loa did, said Emily Brodsky, a professor of Earth and planetary sciences at the University of California at Santa Cruz.

“People are hesitant to assure the public there’s going to be a long warning,” she said. “Stealth eruptions exist.”