Underwater eruption off the east coast of Mayotte / Volcano

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News and updates on the activities of the volcano on the island of Mayotte:

Update on the activity of the volcano on the island of Mayotte (France, western Indian Ocean): underwater eruption off the east coast of Mayotte

Fri, 25 Dec 2020, 12:34
12h34 | PAR: PD

Map of earthquakes greater than magnitude 3.8 from May 10, 2018 to October 29, 2018. Purple and blue earthquakes occurred early in the crisis while yellow and red earthquakes occurred months later. The average horizontal error on the location is approximately 15 km. Thus, we cannot see an orientation of the earthquakes in one of the two swarm regions.


Differential bathymetry applied to map the thickness of the May-June 2019 lava flow south of the new volcano.
Map of earthquakes that occurred from May 12, 2020 to October 1, 2020, manually located using land-based seismological stations and ocean floor seismometer (OBS) data.  The location of the epicenter is more precise than two years ago (the color of the dots corresponds to the estimated horizontal error on the location), and smaller magnitudes (the size of the dots corresponds to the magnitude) are detected.  The two seismic zones are visible, and further east, the new volcano is represented by a red triangle.
Map of earthquakes that occurred from May 12, 2020 to October 1, 2020, manually located using land-based seismological stations and ocean floor seismometer (OBS) data. The location of the epicenter is more precise than two years ago (the color of the dots corresponds to the estimated horizontal error on the location), and smaller magnitudes (the size of the dots corresponds to the magnitude) are detected. The two seismic zones are visible, and further east, the new volcano is represented by a red triangle.

In May 2019, a new volcano was discovered 50 km off the east coast of Mayotte by temporal comparison of bathymetric data. It lies on the seabed at a depth of 3500 m. It is 820 m high and the estimated erupting volume is greater than 5 km3.

Indeed, since May 2018, seismic activity has affected Mayotte. The earthquakes off Mayotte are grouped into two main areas: the main one is located between 5 and 15 km east of Petite Terre and appeared later, at the end of August 2018, while the secondary, which appeared in early May, was ‘about 25 km east of Petite Terre and 25 to 50 km deep. The most significant earthquakes are in the secondary swarm area, including a Mw5.9 earthquake that occurred on May 15, 2018. Since July 2018, the number of earthquakes has decreased slightly, but seismicity continues regularly at low to moderate magnitudes.

The discovery of the submarine volcano explains the seismic swarms that have occurred since May 10, 2018 and, although this seismic activity is not directly under the new volcano, further east the two swarm regions are linked to the volcano by magmatic routes. Indeed, during the MAYOBS-1 campaign, scientists observed plumes (which do not reach the surface) by acoustic imaging of the water column above the summit of the volcano (the plume was 2 km high ) and over the swarm region about 10 km off Petite Terre, showing that there are also thermal anomalies in the swarm region 10 km off Petite Terre.

Geodesic observations can also be explained by volcanic activity. Since May 2018, Mayotte’s GPS stations have been moving east and sagging. These movements can in fact be explained by the deflation of a deep magma reservoir east of Mayotte. Displacements were strongest at the start of the crisis, which probably means that the rate of deflation of the reservoir, and therefore the flow of magma, was at its strongest at the start of the eruption.

In June 2019, the MAYOBS-2 campaign uncovered a new lava field 25 to 75 m thick covering more than 8 km2 south of the volcano.

In July 2019, the MAYOBS-3 and MAYOBS-4 campaigns identified a new lava flow on the western flank of the submarine volcano. It is over 150 m thick and its estimated volume is 0.3 km3.
Fluid emissions and plumes of volcanic origin were also detected. These plumes do not reach the surface. Those at the top of the new volcano, detected in May and June, no longer existed, while others, smaller, were detected on the new flow. In addition, the first photos of the new seabed were taken and showed both pillow lavas and cord lavas (more fluid).

From the second half of 2019, the location of volcanic activity seems to have changed. Indeed, since August 2019, the horizontal displacement vectors point more to the north than before, and this change of direction can be explained by a relative displacement of the source of pressure (the magma), which has moved from 20 to 25 km northwest of its location. The new lava flow discovered by the following campaign (MAYOBS-13) in May 2020 was also northwest of the volcano. It covered 5 km2.

In October 2020, the BAYOBS-15 campaign showed that new lava flows up to 60 m thick were emitted north-west of the volcano, near the secondary seismic zone. Plumes already discovered are still observed in the main seismic zone 10 km east of Petite Terre, and a new plume was discovered in this zone.


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