Seimsmologists describe drainage of deep magma reservoir in Indian Ocean

Thanks to a survey of seismic activity in the Indian Ocean, scientists have described the drainage of one of the deepest and largest known active magma reservoirs in the upper mantle.

In 2018, a new submarine volcano was formed off the coast of the island of Mayotte, part of the Comoros archipelago situated between the African mainland and Madagascar. By studying a series of seismic signals, known as very long period signals, or VLPs, originating from off the coast of Mayotte, researchers were able to characterize the young volcano's formation.

For some time, the ocean floor off the coast of Mayotte has hosted swarms of thousands of earthquakes, quakes scientists suspected were tectonic in origin. But in June of 2018, a new seismic signal emerged -- very long period signals.

The seismic sound produced by VLPs recall the toll of a large bell. The low-frequency signals, which last 20 or 30 seconds each, were quite harmonic.

VLTs are associated with the movement of magma in the mantle, and the deep pitch of the seismic bell tolls -- described Monday in the journal Nature Geoscience -- suggested the signal was originating from a very large magma chamber.

Scientists at the GFZ German Research Center for Geosciences did their best to analyze the specifics of the region's evolving seismic signals, but their efforts were complicated by the lack of seismic sensors surrounding Mayotte.

"We tried to improve the unfavorable initial situation by developing special new analytical methods such as cluster and directional beam methods," GFZ researcher Simone Cesca said in a news release.

Their survey methods showed the initial swarm of seismic signals was created by the movement of magma from the large reservoir to the surface. Once the seabed was breached and an open channel was created, the magma began to flow more efficiently and a new submarine volcano was formed.

Data collected by a French oceanographic campaign recently confirmed the presence of the new ocean floor volcano.

Shortly after the formation of the volcano, levels of tectonic seismic activity decreased. The ground on the island of Mayotte also began to sink, and VLP signals returned.

"We interpret this as a sign of the collapse of the deep magma chamber off the coast of Mayotte,"

said researcher Eleonora Rivalta.

Because all this action took place several thousand feet beneath the ocean surface, no one noticed the eruption. But the presence of the new volcano could pose risks to the surrounding islands. Future eruptions and collapses within the emptying magma chamber could trigger larger earthquakes in the future.

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