A new undersea volcano is born east of Africa- Times Of Nation
The largest submarine volcanic eruption ever recorded began on 10 May 2018 off the eastern shores of Mayotte, a group of islands off the coast of Mozambique and north of Madagascar. Then and there, a highly viscous and ductile volume of molten rock from Earth’s upper mantle pierced the cooler and more brittle lithosphere layer above and erupted lava onto the seafloor.
That day, people in Mayotte felt a large earthquake, and a magnitude 5.8 event struck on 15 May. Over the next few weeks, the magmatic dynamics generated a few very low-frequency earthquakes and thousands of deep ones. The result of all that geophysical activity was a new mountain on the seafloor. (To learn about other submarine volcanoes, see Physics Today, August 2012, page 16.)
The French geological survey called Nathalie Feuillet of the University of Paris and other experts to study the seismic activity. As the chief scientist of a May 2019 research cruise, Feuillet led an effort to collect seismic and surface deformation data of the volcanic eruption. They found that the new undersea volcano now stands 820 meters tall and lies at the end of a series of recent lava flows that form a 50 km ridge. The geological feature is likely part of an extensional tectonic structure formed by fissures and faults associated with the East African Rift to the west.
On the 2019 cruise, Feuillet and the other researchers on the ship used an echo sounder to bounce sound waves off the ocean floor across an area of 8600 km2, roughly the size of Puerto Rico. Those data, once fed into a digital terrain model, revealed the Mayotte volcanic ridge, shown in the right-hand image below. (The left-hand image of the ocean floor, as mapped in 2014, indicates a relatively flat seafloor topography.)
To learn more about the new volcano, which spewed about 5 km3 of lava, coauthors Claudio Satriano, Angèle Laurent, and Pascal Bernard analyzed seismic wave data collected by a network of seismometers on land and on the seafloor, most of which were installed or deployed after the 2018 eruption.
The network detected some 17 000 events from 25 February to 6 May 2019, 94% of which cluster on the western segment of the Mayotte ridge and 25–50 km below the surface. An additional 84 earthquakes were identified and classified as very low-frequency events, with periods of 15 seconds. The very low-frequency earthquakes were likely generated by a seismic source that was repeatedly excited, possibly faults destabilized by magma in a large, deep reservoir.
To have so many earthquakes deep in Earth’s interior is unusual- Many seismic events caused by volcanic activity occur above the Moho—the boundary between the crust and mantle, about 17 km below the surface of Mayotte. The researchers interpret the deep earthquakes as evidence of geodynamic activity in the upper mantle and lower crust. Magma from the upper mantle likely filled a reservoir and pressurized the region. As the magma traveled through the crust and eventually to the seafloor, it would have instigated swarms of deep earthquakes. (N. Feuillet et al., Nat. Geosci., 2021, doi-10.1038/s41561-021-00809-x.)
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