Scientists Just Mapped The Underbelly Of Hawaii’s Volcanoes In Stunning Detail

For decades, a mysterious swarm of earthquakes has rumbled below the small town of Pahala, near the southern coast of the island of Hawaii. By 2015, the rate of tremors underground had risen from around seven to 34 earthquakes per week. And the year after the 2018 Kilauea eruption, the largest Hawaii has seen in centuries, earthquakes reached a fever pitch.

Nearly 500 earthquakes have struck below Pahala every week, and intensified activity has not stopped. “We’re like an earthquake power station down here,” he says lou daniele, General Manager of Ka’u Coffee Mill in Pahala. “It’s just become a constant part of daily life.”

Now, scientists have discovered the source of this geological uproar: A stack of interconnected features some 22 to 26 miles underground is slowly swelling with molten rock. As magma pulses intrude on the pancake-shaped structures, known as umbrals, a cascade of earthquakes rumbles along their length. These pulsating magmatic roots may even provide a conduit carrying molten rock toward Kilauea and Mauna Loa, two of the world’s largest and most active volcanoes.

“We were going crazy,” he says wild johngraduate researcher at the California Institute of Technology and lead author of a new study describing the geological features in Sciences. “No one had directly observed magmatic activity on this scale before.”

The researchers used machine learning algorithms to search for earthquakes in seismic data from the Hawaii Volcano Observatory sensor network, detecting tremors so small that previous methods missed them. The result is an astonishingly detailed portrait of Hawaii’s fiery underworld, which promises to help scientists sort out the geological processes driving the island’s volcanoes.

“This will probably be the future of volcano science,” he says. matt burgessformer seismic analyst in Hawaii who has studied the earthquakes deep below Pahala.

Mysterious Rumors from the Deep

The Pahala earthquake swarm has been rumbling since at least 1970. The earthquakes are located in the mantle, the layer of our planet between the crust and the core, and most of them are too small and deep to shake the surface very much. force. Instead, the tremors feel more like a swaying or swaying of the ground. Sometimes Daniele from Ka’u Coffee only realizes something is wrong because ripples appear on the surface of his coffee. But in recent years, the noises below Pahala have become relentless.

“The seismicity just kept going up and up,” he says nymph benningtona volcano seismologist with the USGS Hawaii Volcano Observatory who has been tracking the recent surge in activity.

Pahala is believed to sit atop the head of a searing column of rock, called a hotspot, that built the Hawaiian Islands. As the Pacific plate moves through the stationary hotspot, new volcanoes and eventually new islands are born. The 15 volcanoes on the Hawaiian Islands are the youngest in a chain of more than 129 who has created the hotspot, most of which have gone silent and are now hidden under the waves.

Previous studies have identified probable sources of molten rock below the quake swarm and suggested that an ascending pulse of magma could be driving the deep shaking. Other studies have detailed shallow volcanic plumbing. But it is not known exactly how molten rock flows from deep in the mantle.

“We’re basically missing this big piece,” says Bennington.

The quake swarm was an opportunity to get a closer look at the burning underbelly of the island. While earthquakes can come from many sources, the magma or fluid moving through the cracks makes telltale seismic noises. And as molten rock drifts, it can stress nearby soil, causing it to crack and shift, which scientists can also detect in earthquake data.

By plotting all these earthquakes in three dimensions, a bit like geological pointillism, scientists have now sketched out a network of subterranean structures where magma can flow to the surface, carrying volcanic eruptions.

a seismic treasure

Amid increased seismic activity in Hawaii, Wilding joined geophysicist by Zachary Ross research group at Caltech. Ross had been developing methods that detect earthquakes using machine learning algorithms, which can detect surprisingly small quakes and give stunning spider web views of underground fault zones.

The team applied these methods to 3.5 years of seismic data from Hawaii, recorded between 2019 and 2022. The system identified nearly 200,000 earthquakes from the swarm, illuminating stacked sill structures in the upper mantle. The extreme detail even allowed scientists to track magma as it seeped into a sill, triggering a cascade of earthquakes.

When Ross first saw the details of the geological structures on his computer screen, he was flabbergasted. “It was like, oh my gosh, what are we looking at here?” he says. “It’s just shocking.”

He describes the sill complex as the “gateway to the system”, providing a means to transport magma horizontally away from the area below Pahala. These underground features do not contain void space, but instead represent a weak zone in the rock where magma has infiltrated and spread as a molten sheet. The complex links to a fracture zone which leads to Kilauea, as well as an area the team believes to be connected to Mauna Loa.

There may be more than one route that molten rock takes to the surface, Ross says. He speculates that the sills could even be part of a broader layer of structures below the island that transports magma to the different volcanic peaks.

The timing of the deep earthquakes is another indication that the umbral structures are connected to volcanoes on the surface. On the same day that Kilauea erupted in 2020, the sills rumbled with earthquakes. A similar eruption and a spike in deep quakes occurred in 2021, and Wilding says these eruptions may have released pressure in magma pipes, pulling up more molten rock from deep below.

magma highways

The latest study opens new windows into the fiery depths of our planet, getting scientists excited about what could happen next. “I was surprised by the incredible richness of the new earthquake catalog they developed and the amount of detail it shows,” says the volcanologist. roman diana from Carnegie Science, who was not part of the study team. “I want more.”

She and other researchers are eager for the team to extend the catalog to 2015 or earlier to get an even more detailed look at the system and its series of fiery attacks. A more extensive catalog could also help explain the 2019 wave of earthquakes, which followed Kilauea’s eruption the previous year and triggered some 200 billion gallons of lava.

Roman points out that it is still unknown if nearby volcanoes directly hit the magma on the sills. she and burgess published a study last year that suggests an indirect link between the eruptions and deep earthquake swarms. Inflation of magma deposits deep within Pahala could compress nearby channels of molten rock that lead to Mauna Loa and Kilauea, like squeezing a tube of toothpaste. Or, says Roman, both processes could be at play.

This summer, Bennington and his colleagues plan to deploy an extensive network of seismic sensors at Kilauea to further complete the underground picture. She says the new study has made her particularly interested in looking for signs of magma in the proposed pathways connecting the sills and nearby volcanoes.

“Each study puts a new piece in…the puzzle,” she says. “They add something really amazing here.”

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