Scientists had suspected that somewhere beneath Hawaii, a secret was entombed in stone, something that played a part in influencing the famous volcanism of the island chain. Now, with the help of nearly 200,000 earthquakes and a machine learning program, Wilding and his colleagues have finally figured it out.
In a study published Thursday in the journal Sciences, the team has revealed a previously hidden collection of magma caches that may act as the beating heart of the volcanoes above. The discovery offers a possible solution to a longstanding mystery: how does magma travel from the deep mantle to the surface of Hawaii? The work gives scientists a valuable new window into the behavior of some of Earth’s most capricious and dangerous volcanoes.
The shallow magma reservoirs that fuel eruptions in Hawaii have been known for some time. This is partly due to seismic waves, which are closely monitored in Hawaii by an ever-expanding network of sensors. The waves act like an ultrasound for the Earth; changes in their speed and trajectory during their journeys underground tell scientists what kind of matter they have been traveling through, providing clues about its temperature, density, and composition.
But to really understand what drives these volcanic powerhouses, scientists need to know what’s happening at the interface of the soft mantle and solid crust. That’s what the new study finally reveals in unexpected detail.
The giant feature described in the paper is made up of several elongated chambers called thresholds. When eruptions drain magma from surface deposits above, these deep sills appear to react. A cacophony of earthquake signals as individual chambers start to fill with molten rock at different times, a bit like “blood rushing into a heart,” Wilding said.
“We were looking at it, and it was amazing, it really was,” he said. zachary ross, a geophysicist at Caltech. “Since then, I can’t get the image out of my head.”
ken rubinA volcanologist at the University of Hawaii who was not involved in the study said: “It’s a very elegant study and an immensely intriguing result.”
Like much of the planet, Hawaii would not exist without volcanism. Since time immemorial, a deeply embedded source of superheated rock known as a mantle plume has been setting the underside of the Pacific tectonic plate ablaze. As the plate has continued to drift, a succession of epic volcanoes has risen above the waves, creating the Hawaiian island chain.
Today, the chain is home to a small family of active volcanoes, including Mercurial. mauna loa and the hyperactive Kilauea on the Big Island, which stopped erupting simultaneously this month.
A persistent seismic rumble from an area southwest of Kilauea and 20 miles underground had previously suggested that a glitch collection they can exist there, creating pathways for magma to travel from the Hadean depths to near-surface reservoirs. And since the 1980s, special types of earthquakes that suggest roaming fluids have hinted that magma has been churning in the region. But until recently, the true nature of this underground labyrinth was based more on speculation than scientific truth.
“It’s been this mystery box on the mantle,” Wilding said. “We really have very little idea what’s going on.”
What the scientists needed was a sustained spike of earthquakes coming from that exact region, enough to brightly illuminate that shadowy area. Things looked promising in 2015 when the rumble from the region picked up a bit.
But the team’s lucky break came in 2018 when, after Kilauea had been erupting more or less continuously for 35 years, a grand finale eruption sequence It started on the volcano. The event produced lava equivalent to 320,000 Olympic swimming pools in just three months, and the rapid exsanguination of the volcano’s shallow magma reservoir caused its summit to collapse dramatically.
In an exciting plot twist, geologists recorded a shocking increase in deep seismic activity in 2019 well below the town of Pāhala, which lies roughly 25 miles southwest of Kilauea. Surely, the scientists thought, this cannot be happening.
While the Pāhala earthquake storm was an opportunity to unearth the island’s buried magmatic treasure, scientists alone would not be able to identify many of the individual quakes in that cacophony, especially the more common small ones that could be quelled by larger explosions. large.
Unwilling to miss a single beat of the geological drum, the Caltech team fed the entire recording of the seismic storm into a machine learning program, a technique Ross and his colleagues had previously used to Identify millions of hidden earthquakes in California. The program quickly learned what was a real earthquake and what was strange noise, then identified and characterized thousands of tremors that conventional seismic signal detection programs and their human analysts would have missed.
From November 2018 to April 2022, the system recorded about 192,000 earthquakes below Pāhala. By plotting these luminiferous points on a map, the team was surprised to discover a collection of pulsating magmatic structures: the pulsating volcanic heart of southern Hawaii.
Some of the earthquakes came from a region 28 to 32 miles deep: These long period earthquakes are generally attributed to the vibrations formed by the movement of fluids, including magma. Most of the seismicity came from an area 22 to 27 miles deep. These volcanic tectonic earthquakes, of the type that occur when a fault shifts and rocks break within a volcanic region, outlined a series of nearly horizontal sheet-like structures, some four miles long and three miles wide. broad.
At different times, the scientists detected sudden increases in seismic activity within separate sheets. The team surmised that these sheets were sills, pockets of magma whose own grunts followed molten rock rising from the liquid-filled nether region near the mantle plume’s peak.
In search of a deeper connection
This new 3D map of a key segment of the Hawaiian circulatory system “is extraordinary,” he said. Jackie Caplan Auerbach, a volcano seismologist at Western Washington University who was not involved in the new study. It’s “terribly cool,” he said, that scientists can not only see this previously hidden heart, but also sense the convulsions of the internal ventricles.
The Pāhala Sill complex, as the heart is technically known, appears to have several arteries branching off it. A main path, scarred by rock-shattering earthquakes, appears to lead directly into one of Kilauea’s shallow magma reservoirs. So perhaps it’s no coincidence that the sill complex began roaring relentlessly in 2019. During the 2018 eruption, Kilauea ran out of a significant portion of its shallow magma supply, causing a drop in pressure. In response, the sills sucked in magma to equalize the pressure. Similar events happened during the Kilauea War. shortest eruption of 2020.
Further work may help resolve the vexed question of whether Kilauea and Mauna Loa, which are relatively close neighbors on the surface, are somehow connected to great depths. To date, there is little concrete evidence for this hypothesis, and experts generally agree that the two volcanoes is it so largely Independent each other
The new study doesn’t overturn that consensus yet. It shows another main artery of the sill complex, again scarred by rock-shattering earthquakes, heading towards Mauna Loa. But it stops dead on a large horizontal fault line and doesn’t seem to reach one of Mauna Loa’s shallow magma reservoirs.
It is also not certain that the magma is moving through any of these pathways. That would change if future work detects long-period earthquakes coming from them, the kind that signify the presence of fluids, probably magma.
“The results are amazing,” he said. roman diana, a geophysicist at the Carnegie Institution for Science in DC who was not involved in the study. But “it is not yet clear whether the magma being fed into Pāhala directly feeds the eruptions of Mauna Loa and Kilauea.”
Roman has also studied the Pāhala earthquakes. His co-written 2021 paper he concluded that they were the result of magma intrusion at depth, causing simultaneous disturbances at Mauna Loa and Kilauea by squeezing their underlying pipeline networks. The new study supports this notion of an indirect connection. But even with this magmatic web mapped out, a more explicit link is too early to call.
Still, much of the Hawaiian underworld remains unexplored, and more magmatic arteries may still be located, Ross said.
“What else is in there that hasn’t been lit?” he said. Whenever Hawaii’s hellish underground shakes with fury again, the Caltech team will be ready to zoom in, hoping to reveal what for now remains hidden.
