A new lava flow was identified and first seafloor images of the volcano were taken during MAYOBS 3 and MAYOBS 4 oceanographic campaigns. Meetings and feedback with the various stakeholders in Mayotte also took place on board the Marion Dufresne.
The last two oceanographic campaigns, "MAYOBS3" and "MAYOBS4", financed as part of a joint knowledge acquisition programme by the "ministère de la transition écologique et solidaire" and the "ministère de l’enseignement supérieur, de la recherche et de l’innovation", ended on Wednesday 31 July. On this occasion, a scientific presentation was held on board the oceanographic vessel Marion Dufresne. This presentation was organized in two stages: a first stage of exchange between scientists and the various stakeholders in Mayotte (parliamentarians, elected members of the Departmental Council, mayors, experts, members of the pre-selection committee for the attribution of the volcano's name) in the morning ; a second stage in the afternoon with a press conference.
These meetings are part of the Government's desire to ensure transparency in the dissemination of scientific knowledge and to promote understanding of the phenomenon by the population. They were an opportunity to show the data collected during the MAYOBS campaigns and to explain the collective work carried out by scientists from the Institut Français de Recherche pour l'Exploitation de la Mer (Ifremer) and the Bureau des Recherches Géologiques et Minières (BRGM), the Centre National de la Recherche Scientifique (CNRS), the Institut de Physique du Globe de Paris (IPGP) and Strasbourg (IPGS), the University of La Réunion and the University of Clermont Auvergne, under the direction of Nathalie Feuillet (IPGP), Yves Fouquet (Ifremer) and Isabelle Thinon (BRGM).
The MAYOBS3 mission aimed to recover some of the ocean bottom seismometers that are monitoring the area, before their redeployment in September 2019. The seismometers remaining on the bottom will allow for further monitoring.
The "MAYOBS3" and "MAYOBS4" campaigns mapped the volcanic ridge between the active volcano (about 50 km from the island) and the seismic zone (about 15 km from the island).
Seismicity has decreased. The earthquakes are deep (20 to 50 km). Some deep earthquakes have also been located between the main seismic zone (15 km from the island) and the land. These earthquakes occurred since the beginning, but they had not been located during previous missions due to their low magnitude (between 1 and 3).
A new lava flow identified
The data collected confirm that the height of the volcano has not changed (peak at a depth of 2850 meters). However, since June, a new volcanic flow has been identified on the western flank of the underwater volcano. Its thickness reaches more than 150 meters. The estimated volume is 0.3 km3.
The "MAYOBS3" and "MAYOBS4" campaigns also detected fluid emissions and plumes of volcanic origins. These plumes do not reach the surface. Those at the top of the new volcano, detected in May and June, no longer exist, while others, smaller, have been detected on the new flow.
The first images of the seafloor
Two "Scampi" dives (using a seafloor camera) were carried out on the volcano. They show pillow lava and corded lava typical of more fluid lava. Fluid samples were also collected from the plumes and analyses are now carried out.
Rock samples were taken from recent flows using four dredges.
The MAYOBS campaigns have therefore enabled a very rich collection of data. The scientific teams will continue to analyse this data on land to better understand the potential risks associated with these seismo-volcanic phenomena.
More information :
> Press release (in french) on the "préfecture de Mayotte" website