Largest underwater eruption ever recorded creates massive new volcano

A major seismic event that began in May 2018 and was felt around the world officially gave birth to a new underwater volcano.

Off the east coast of the island of Mayotte, the gigantic new element rose 820 meters (2,690 ft) above the sea floor, an unprecedented advantage before the earthquake that hit the island in May 2018.

“This is the largest active submarine eruption ever documented.” write the researchers in their work.

The new feature, believed to be part of the tectonic structure between the East African fissure and the Malagasy, is helping scientists understand deeper Earth processes of which we know relatively little.

The seismic rumbling of the ongoing event began on May 10, 2018. Just days later, on May 15, a magnitude 5.8 earthquake rocked a nearby island. At first the scientists were confused; but it didn’t take long to find out that a volcanic event had occurred as never seen before.

The signal points to a location about 50 kilometers from the east coast of Mayotte, a French territory and part of the volcano Comoros Islands sandwiched between the east coast of Africa and the northern tip of Madagascar.

So a number of French government agencies sent a research team to check this; there is indeed a seamount that has never existed before.

Under the direction of geophysicist Nathalie Feuillet of the University of Paris in France, the scientists have now described their results in a new paper.

The team began monitoring the area in February 2019. Using multibeam sonar, they mapped an area of ​​8,600 square kilometers on the ocean floor. They also placed a network of seismometers on the ocean floor, to a depth of 3.5 kilometers, and combined it with seismic data from Mayotte.

Between February 25 and May 6 2019, this network detected 17,000 seismic events from depths of about 20 to 50 kilometers below the seabed – a very unusual finding since most earthquakes are much shallower. The other 84 events are also very unusual and seen at a very low frequency.

With this data, the researchers were able to reconstruct how new volcanoes might emerge. According to their findings, it started with a magma reservoir deep in the asthenosphere, the layer of molten mantle directly beneath Earth’s lithosphere.

Chronology of the epidemic. (Feuillet et al., Natural Geoscience, 2021)

Beneath the new volcano, tectonic processes may have damaged the lithosphere, producing dikes that drain magma from the reservoir through the crust, creating a swarm of earthquakes. Eventually this material ends up on the ocean floor where it erupts, producing 5 cubic kilometers of lava and building a new volcano.

The low-frequency events were likely generated by shallower fluid-filled cavities in the crust that may have been repeatedly stimulated by seismic stress on faults near the cavity.

In May 2019, the volume of new volcanic edifice extruded was between 30 and 1,000 times greater than forecast for another deep-sea eruption, making it the most significant underwater volcanic eruption ever recorded.

“The volumes and flows of lava emitted during magmatic events at Mayotte are comparable to those observed during eruptions at Earth’s largest hotspots.” researchers write.

“Future scenarios could include a new caldera collapse, an underwater upslope eruption, or a land eruption. Large lava flows and cones on Mayotte’s upper slopes and on land suggest this has happened in the past.

“Since the discovery of new volcanic structures, an observatory has been established to monitor activity in real time, and continue to track the evolution of eruptions and structures.”

This study was published in Natural geoscience.

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