A stock photo showing lava pouring
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A stock photo showing lava pouring into the ocean at Kīlauea Volcanic eruption in Hawaii on the Big Island, unrelated to the underwater volcano. Scientists have recorded the largest underwater volcanic eruption of lava, which created a new volcano on the seafloor in the Indian Ocean.
The largest underwater eruption ever recorded has created a volcano on the seafloor that is 2,690 feet tall.

The volcano, which is twice as tall as the Empire State Building, was not present off the eastern coast of the island of Mayotte in the Indian Ocean before an earthquake shook the island 2018.

The underwater seismic event generated over 11,000 detectable earthquakes in what the authors of a Nature paper documenting it describes as a "major magmatic event." The event, which caused the deformation of the seafloor was so great it was registered beyond the Indian Ocean and around the globe.

"Volcanic eruptions shape Earth's surface and provide a window into deep Earth processes," the authors said. "This is the largest active submarine eruption ever documented."

The authors added that the new volcanic edifice is located at the tip of a 31-mile-long ridge created by other recent lava flows. This new structure runs between the East Africa and Madagascar rifts and could help researchers better understand the processes that drive tectonic activity on Earth.

The earthquakes began on May 10, 2018, and were followed by a magnitude 5.8 quake five days later. Scientists investigating the seismic event discovered that it was an underwater volcanic eruption on a scale researchers hadn't recorded previously.

A team of scientists led by University of Paris geophysicist Nathalie Feuillet, also lead author of the Nature paper, placed a range of tech devices including seismometers on the ocean floor in the area to determine the origin of the seismic activity. They also surveyed the region with an echosounder which used radar signals to reveal the 2,690-foot-tall volcanic structure.

Between the end of February and the beginning of May 2019, the team discovered around 17,000 seismic events at a depth of between 12 and 31 miles beneath the ocean floor—deeper than most earthquakes. Searching at low frequencies they also found a further 84 events.

The data collected by the team allowed them to piece together the events that led to the creation of the new volcano. They believe that tectonic processes may have damaged the solid outer part of Earth including the crust and mantle known as the lithosphere.

This caused magma reservoirs beneath this layer to rise to the upper layers through dikes and also triggered faults that already existed in the mantle to be reactivated. They caused the earthquakes and led to magma flowing to the seafloor where it erupted to cause the production of a cubic mile of lava and the new volcano.

The authors said that the eruption was not only the largest ever recorded on the seafloor but was six times smaller than what is considered the largest volcanic eruption since records began, Iceland's 1783 - 1784 Laki eruption.

"The volumes and flux of emitted lava during the Mayotte magmatic event are comparable to those observed during eruptions at Earth's largest hotspots," the authors said.

As of May 2021, when the paper was written, the authors say that the earthquakes were still continuing and the seafloor in the region was continuing to deform.

Aside from the creation of this new volcano, the event marks the first time that earthquakes have been measured off the coast of the French island since 1972, and the most recent volcanic activity in the area dates back between 4,000 and 6,000 years ago.

"Future scenarios could include a new caldera collapse, submarine eruptions on the upper slope or onshore eruptions," concluded the authors. "Large lava flows and cones on the upper slope and onshore Mayotte indicate that this has occurred in the past."