Mauna Loa, Earth’s largest active volcano, suddenly awoke on November 27 after nearly 40 years of slumber. The volcano shot lava fountains as high as 50 meters into the air as rivers of molten rock flowed down the sides of the volcano to Saddle Road, the main road on Hawaii’s Big Island.
Mauna Loa stands shoulder to shoulder with four other volcanoes, the explosively dramatic Kilauea (SN: 7/16/18and Mauna Kea murmuring quietlySN: 5/14/20). Kilauea Lake caught fire in recent years with its pyrotechnics while Mauna Loa fell asleep. But the sleeping giant has not been so quiet in the past, says Ingrid Johanson, a geophysicist at the Hawaiian Geological Survey’s Hilo Volcano Observatory.
Historically, he said, Mauna Loa would rise every seven years or so on average. This last space between eruptions is “quite a big gap”.
Science News spoke with Johanson about how Mauna Loa tends to wake up, what lava is in the way and what kind of neighbors Kilauea and Mauna Loa are.
Were there signs warning that Mauna Loa was about to erupt?
“It depends on what you want to advise,” says Johanson. “Simply speaking, we know that Mauna Loa has shown signs of disturbance since 2015.” At the time, he says, there was an uptick in the rate of local earthquakes, as well as in GPS observations of ground deformation — the upward swelling of the earth’s surface that indicates magma is moving below.
Those signs have tapered off a bit and then increased again over the next six months, suggesting that “the situation is evolving,” says Johanson. But when the volcano erupted, he could not decide. “We had about an hour and a half warning,” he said. That was the time between when the researchers noticed the sudden earthquakes, the impending eruption and the lava flow.
He adds that the brief notice is “true form” for Mauna Loa. Other eruptions developed very rapidly in the same way.
How is monitoring Mauna Loa different than it was before the last eruption in 1984?
“One of the big differences between 1984 and now is the technology,” says Johanson.
“We may see more earthquakes” [and] to detect seismic waves at a wider range of frequencies. And we have GPS and similar electronics to measure the deformation continuously. That technique allowed scientists to detect not only what was the recent deformation of the earth, but also how it was changing over time, giving a small amount of warning time.
That was not possible 40 years ago. The researchers then returned to measure the deformation by hand, hiking to the top of the mountain every few weeks or so. “There was a technique called EDM, electronic distance measurement, which essentially shined a laser on the weight so you could get very accurate distance measurements,” says Johanson. Subtle changes in the place of the weight, installed in the mount, helped reveal the deformation.
Does the current eruption pose a threat to the people?
“It’s too early to tell — it’s not yet clear how much volume we can expect from this eruption,” says Johanson. “I don’t think this is a given that the eruption is more important than the past, but the feeling is that maybe it’s going back to business as usual, like a volcano.”
The good news is that the lava flow is not currently a threat to communities on the Big Island. But Saddle Road connects the east and west sides of the island, Johanson notes. “If the lava went through the road, it would really impact the island.”
But the eruption disrupted data collection for one of climate science’s most iconic charts: the Keeling Curve, a nearly 60-year continuous record of atmospheric carbon dioxide that shows a steady rise in levels of the gas.
Carbon dioxide data collected from instruments at the Mauna Loa Observatory. The eruption of power was cut off for observation on November 28. as of November 30, power had not yet been restored, and the lava had blocked access to the site. For now, it’s unclear if the outage will have a lasting impact on data collection.
Kilauea has been erupting more or less continuously for decades. How are Kilauea and Mauna Loa connected?
The two volcanoes are separated by geochemically distinct lavas, suggesting their own lead systems—the networks of tunnels and channels through which magma moves—are separated. That plumbing separation probably occurs under the crust and in the mantle, says Johanson, when the volcanoes eventually hit the same hot spot in the mantle.SN: 1/6/22).
That said, Kilauea and Mauna Loa are neighboring volcanoes, communicating through changes in pressure and stress underground, he says. Changes in pressure in the plume beneath one volcano can subtly affect another, for example, by changing how easy it is for one volcano to expand, making way for magma to move. “Species do little to each other.”
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