By Laura Geggel - Associate Editor
(Image: © Shutterstock)
Mysterious seismic hums detected around the world were likely caused by an unusual geologic event — the rumblings of a magma-filled reservoir deep under the Indian Ocean, a new study finds.
These odd hums were an unconventional geologic birth announcement. A few months after the sounds rippled around the Earth, a new underwater volcano was born off the coast of the island of Mayotte, located between Madagascar and Mozambique in the Indian Ocean.
The new findings provide a detailed, one-year timeline of the newborn volcano's birth, which would make any mother (in this case, Mother Earth) proud. The study details how magma from a reservoir about 20 miles (35 kilometers) under the ocean floor migrated upward, traveling through Earth's crust until it reached the seafloor and created the new volcano.
"It took only [a] few weeks for the magma to propagate from the upper mantle to the seafloor, where a new submarine volcano was born," study lead researcher Simone Cesca, a seismologist at the GFZ German Research Centre for Geosciences in Potsdam, Germany, told Live Science in an email.
This illustration shows how magma in a reservoir deep underground ascended to form a submarine volcano in the Indian Ocean. (Image credit: James Tuttle Keane/Nature Geoscience (2020))
A volcano is born
The saga began in May 2018, when global earthquake-monitoring agencies detected thousands of earthquakes near Mayotte, including a magnitude-5.9 quake, the largest ever detected in the region. Then, in November 2018, seismologists recorded weird seismic hums, some lasting up to 40 minutes, buzzing around the world. To put it mildly, these mysterious hums "trigger[ed] the curiosity of the scientific community," the researchers wrote in the study.
The researchers found more than 400 such signals, Cesca said.
In 2019, a French oceanographic mission showed that a new volcano had been born near Mayotte. It was huge, measuring about 3.1 miles (5 km) long and almost a half mile (0.8 km) high.
Other researchers have suggested that these mysterious hums were tied to the new volcano and possibly a shrinking underground magma chamber, given that Mayotte has sunk and moved several inches since the earthquakes began. However, that research has yet to be published in a peer-reviewed journal.
In the new study, the researchers used data gathered worldwide, as there wasn't any local seismic data available from Mayotte. Their analyses show that two major stages led to the volcano's birth. First, magma from a 9-mile-wide (15 km) reservoir flowed upward diagonally until it reached the seafloor, leading to a submarine eruption, Cesca said. As the magma moved, it "triggered energetic earthquakes along its path to the surface," he said. "In fact, we reconstructed the upward migration of magma by following the upward migration of earthquakes."
A sketch showing the deep magma reservoir and the magma highway that led to the new submarine volcano in the Indian Ocean. (Image credit: Cesca et al. 2019, Nature Geoscience)
In the next stage, the magma path became a highway of sorts, allowing magma to flow out of the reservoir to the seafloor, where it built the volcano. As the reservoir drained, Mayotte sank almost 8 inches (20 centimeters). It also caused the area above the reservoir, called the overburden, to weaken and sag, creating small faults and fractures there. When earthquakes related to the volcano and tectonic plates shook this particular area above the reservoir, they triggered "the resonance of the deep reservoir and generate[d] the peculiar, very long period signals," Cesca said. In other words, those strange seismic hums.
Related: Photos: Hawaii's New Underwater Volcano
In all, about 0.4 cubic miles (1.5 cubic km) of magma drained out of the reservoir, the researchers calculated. However, given the vast size of the volcano, it's likely that even more magma was involved, Cesca noted.
Although the volcano is now formed, earthquakes may still rattle the area.
"There are still possible hazards for the island of Mayotte today," study senior researcher and head of the section Physics of Earthquakes and Volcanoes at the GFZ Torsten Dahm, said in a statement "The Earth's crust above the deep reservoir could continue to collapse, triggering stronger earthquakes."
The new study was published online Monday (Jan. 6) in the journal Nature Geoscience.
A volcano is born
The saga began in May 2018, when global earthquake-monitoring agencies detected thousands of earthquakes near Mayotte, including a magnitude-5.9 quake, the largest ever detected in the region. Then, in November 2018, seismologists recorded weird seismic hums, some lasting up to 40 minutes, buzzing around the world. To put it mildly, these mysterious hums "trigger[ed] the curiosity of the scientific community," the researchers wrote in the study.
The researchers found more than 400 such signals, Cesca said.
In 2019, a French oceanographic mission showed that a new volcano had been born near Mayotte. It was huge, measuring about 3.1 miles (5 km) long and almost a half mile (0.8 km) high.
Other researchers have suggested that these mysterious hums were tied to the new volcano and possibly a shrinking underground magma chamber, given that Mayotte has sunk and moved several inches since the earthquakes began. However, that research has yet to be published in a peer-reviewed journal.
In the new study, the researchers used data gathered worldwide, as there wasn't any local seismic data available from Mayotte. Their analyses show that two major stages led to the volcano's birth. First, magma from a 9-mile-wide (15 km) reservoir flowed upward diagonally until it reached the seafloor, leading to a submarine eruption, Cesca said. As the magma moved, it "triggered energetic earthquakes along its path to the surface," he said. "In fact, we reconstructed the upward migration of magma by following the upward migration of earthquakes."
A sketch showing the deep magma reservoir and the magma highway that led to the new submarine volcano in the Indian Ocean. (Image credit: Cesca et al. 2019, Nature Geoscience)
In the next stage, the magma path became a highway of sorts, allowing magma to flow out of the reservoir to the seafloor, where it built the volcano. As the reservoir drained, Mayotte sank almost 8 inches (20 centimeters). It also caused the area above the reservoir, called the overburden, to weaken and sag, creating small faults and fractures there. When earthquakes related to the volcano and tectonic plates shook this particular area above the reservoir, they triggered "the resonance of the deep reservoir and generate[d] the peculiar, very long period signals," Cesca said. In other words, those strange seismic hums.
Related: Photos: Hawaii's New Underwater Volcano
In all, about 0.4 cubic miles (1.5 cubic km) of magma drained out of the reservoir, the researchers calculated. However, given the vast size of the volcano, it's likely that even more magma was involved, Cesca noted.
Although the volcano is now formed, earthquakes may still rattle the area.
"There are still possible hazards for the island of Mayotte today," study senior researcher and head of the section Physics of Earthquakes and Volcanoes at the GFZ Torsten Dahm, said in a statement "The Earth's crust above the deep reservoir could continue to collapse, triggering stronger earthquakes."
The new study was published online Monday (Jan. 6) in the journal Nature Geoscience.
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Originally published on Live Science.
Strange hums heard around the world traced to new underwater volcano
Ashley Strickland CNN Published Thursday, January 9, 2020
This image provided by NASA Data from six orbits of the
Suomi-NPP spacecraft on April 9, 2015 have been assembled
into this perspective composite of southern Africa and the
surrounding oceans. (NASA via AP)
In 2018, a multitude of seismic signals were detected by earthquake monitoring agencies all over the world in May and June. They created a weird humming sound and some of the signals detected in November of that year had a duration of up to 20 minutes.
The signals and humming triggered "the curiosity of the scientific community," according to a new study that explains what happened: the formation of a new underwater volcano.
The unusual amount of earthquakes were traced to the island of Mayotte in the Indian Ocean, one of several in the Comoros archipelago found between Africa and Madagascar.
Scientists detected 7,000 tectonic earthquakes within the scope of the study. These kinds of earthquakes occur when Earth's tectonic plates become stuck as they move alongside one another. The pressure that allows them to move on causes earthquakes.
The most severe earthquakes reached a magnitude of 5.9 in May 2018.
They also encountered 407 long-period seismic signals. These Very Long Period signals, called VLPs, are harmonic and low, reminiscent of a double bass or large bell. And their 20- to 30-minute signals could be detected hundreds of miles away.
The earthquakes and signals were coming from about 22 miles off the eastern coast of the island. Researchers couldn't see any signs of volcanic activity in this area, but they suspected that magmatic processes may be forming one.
Unfortunately, there was no seismic network on this part of the ocean floor, meaning they were only able to get measurements from the island, Madagascar and Africa.
But they noticed a lowering of the island's surface by seven inches, indicating activity linked to the earthquakes.
New seismological methods developed by the researchers helped them piece together a year-long timeline to reconstruct what happened. Their study published this week in the journal Nature Geoscience.
The first phase involved magma rapidly rising from a reservoir in the mantle 18 miles below the Earth's surface. This opened a channel in the ocean floor, allowing the magma to flow and begin forming a new underwater volcano.
An oceanographic campaign in May 2019 showed that a volcano had formed in the same spot.
During the formation of the underwater volcano, earthquake activity dropped, and the ground of Mayotte lowered. Then, the VLP signals began.
"We interpret this as a sign of the collapse of the deep magma chamber off the coast of Mayotte," said Eleonora Rivalta, study co-author from the German Research Center for Geosciences GFZ. "It is the deepest and largest magma reservoir in the upper mantle to date, which is beginning to empty abruptly."
As dramatic as all of this sounds, it was hardly noticeable on the island itself. Mayotte is one of four volcanic islands in its archipelago and home to about 260,000 people, according to the study. It last erupted about 4,000 years ago.
"Since the seabed lies 3 kilometres below the water surface, almost nobody noticed the enormous eruption," said Torsten Dahm, study co-author and professor of geophysics and seismology at the University of Potsdam in Germany. "However, there are still possible hazards for the island of Mayotte today, as the Earth's crust above the deep reservoir could continue to collapse, triggering stronger earthquakes."
In 2018, a multitude of seismic signals were detected by earthquake monitoring agencies all over the world in May and June. They created a weird humming sound and some of the signals detected in November of that year had a duration of up to 20 minutes.
The signals and humming triggered "the curiosity of the scientific community," according to a new study that explains what happened: the formation of a new underwater volcano.
The unusual amount of earthquakes were traced to the island of Mayotte in the Indian Ocean, one of several in the Comoros archipelago found between Africa and Madagascar.
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Scientists detected 7,000 tectonic earthquakes within the scope of the study. These kinds of earthquakes occur when Earth's tectonic plates become stuck as they move alongside one another. The pressure that allows them to move on causes earthquakes.
The most severe earthquakes reached a magnitude of 5.9 in May 2018.
They also encountered 407 long-period seismic signals. These Very Long Period signals, called VLPs, are harmonic and low, reminiscent of a double bass or large bell. And their 20- to 30-minute signals could be detected hundreds of miles away.
The earthquakes and signals were coming from about 22 miles off the eastern coast of the island. Researchers couldn't see any signs of volcanic activity in this area, but they suspected that magmatic processes may be forming one.
Unfortunately, there was no seismic network on this part of the ocean floor, meaning they were only able to get measurements from the island, Madagascar and Africa.
But they noticed a lowering of the island's surface by seven inches, indicating activity linked to the earthquakes.
New seismological methods developed by the researchers helped them piece together a year-long timeline to reconstruct what happened. Their study published this week in the journal Nature Geoscience.
The first phase involved magma rapidly rising from a reservoir in the mantle 18 miles below the Earth's surface. This opened a channel in the ocean floor, allowing the magma to flow and begin forming a new underwater volcano.
An oceanographic campaign in May 2019 showed that a volcano had formed in the same spot.
During the formation of the underwater volcano, earthquake activity dropped, and the ground of Mayotte lowered. Then, the VLP signals began.
"We interpret this as a sign of the collapse of the deep magma chamber off the coast of Mayotte," said Eleonora Rivalta, study co-author from the German Research Center for Geosciences GFZ. "It is the deepest and largest magma reservoir in the upper mantle to date, which is beginning to empty abruptly."
As dramatic as all of this sounds, it was hardly noticeable on the island itself. Mayotte is one of four volcanic islands in its archipelago and home to about 260,000 people, according to the study. It last erupted about 4,000 years ago.
"Since the seabed lies 3 kilometres below the water surface, almost nobody noticed the enormous eruption," said Torsten Dahm, study co-author and professor of geophysics and seismology at the University of Potsdam in Germany. "However, there are still possible hazards for the island of Mayotte today, as the Earth's crust above the deep reservoir could continue to collapse, triggering stronger earthquakes."
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