Encountering a new volcano

Anne Lemoine is a seismologist in BRGM's Risk and Prevention Division. With her colleagues, she has been following the seismo-volcanic crisis in Mayotte since May 2018 and took part in the MAYOBS 1 sea mission which revealed the underwater volcano, one of the major phenomena behind the crisis.
3 July 2020
Filled rock dredge

Rock dredge containing samples arriving on the deck of the Marion Dufresne.

© BRGM - Anne Lemoine

Extract from the field notes published in BRGM's Geosciences journal No. 24: "Geological information, the latest mapping techniques".

"It all started for our team in May 2018. The island of Mayotte, where BRGM has a local branch, had suffered dozens of earthquakes over the previous few days. My BRGM Seismic and Volcanic Risks unit was called "to the rescue" by BRGM’s local representative. One of my colleagues, Didier Bertil, quickly suspected a swarm of earthquakes.” 

2 May 2019 - Reunion Island 

"We boarded the Marion Dufresne for the MAYOBS sea mission from 2 to 16 May. Numerous scientific organisations were involved: BRGM, Ifremer, IPGP, CNRS-INSU and OVPF. I left with the two marine geophysics geologists from the BRGM Georesources Department, Isabelle Thinon and Fabien Paquet. After a voyage of a few days, we arrived off the coast of Mayotte. Our first objective was to retrieve the ocean bottom seismometers (OBS) installed on the seabed the previous February by the IPGP in order to read the recorded data, analyse it on board and then redeploy them. The teams worked around the clock. We had ten days, not one more, in which to complete our task.” 

9 May 2019 - Discovery of the volcano 

"One year after the beginning of the Mayotte crisis, the mission head and the captain organised a meal on the back deck to thank the crew and the scientific team for their work. Isabelle, my colleague from BRGM, Guillaume, the technician and I were on watch. While the meal was being prepared, many scientists had gathered in the science command post, intrigued by what they were seeing. Arnaud, from Ifremer, had just generated the preliminary bathymetric model (depth map of the seabed) from the data we had acquired. Fabien compared it to the previous 2014 maps. It is at that moment that a new relief was discovered: a cone about 4 km in diameter and 800 m high had clearly emerged above the abyssal plain, which is 3,400 m deep.” 

View of the front deck of the Marion Dufresne at dusk

"We were sailing over an active underwater volcano!”

Anne Lemoine, seismologist au BRGM

14 May 2019 - Rock sampling 

"We tried to get as much information as possible about the volcano. The aim is to recover rock samples by towing a dredge along the bottom. It’s a long process, taking several hours to launch the dredge, drag it along the bottom and then hoist it back on board. As soon as the dredge neared the surface of the water, scientists and sailors came to witness the preview.” 

16 May 2019 - End of the mission 

"I left the ship with Fabien and other team-mates while Isabelle stayed on for the second leg. We were welcomed by our colleagues, who had been supporting us continually from Mamoudzou or Orléans. Following the discovery of the volcano, we had to write reports for the authorities to keep them informed and answer their questions. Their job was then to prepare the messages and measures for the safety of the population.”

Cover of Issue 24 of the Géosciences journal

Cover of Issue 24 of the Géosciences journal.

© BRGM 

Géosciences No. 24: Geological information, the latest mapping techniques

The science of geology is crucial for understanding natural phenomena, as well as for developing and exploiting our country's resources in a viable manner.

This issue includes:

  • a feature about the French Geological Reference Platform – the "geological map of the future", a multi-scale three-dimensional representation of France's subsurface – which will make it possible to publish constantly-updated geological information;
  • an interview with Thierry Dallard, Chairman of the Board of the Greater Paris Council;
  • an interview with Philippe Montagnier from Total concerning the contribution digital services are making to geology;
  • the mission log concerning the discovery of a new underwater volcano in Mayotte.