As part of the actions carried out by the public authorities, to better understand the seismic-volcanic phenomenon that has affected Mayotte since May 2018, a new cruise is being organized off the island from September 11th to 28th, 2023 by the REVOSIMA (Volcanological and Seismological Monitoring Network offshore Mayotte) onboard the Marion Dufresne. The IPGP operates this network through the Piton de la Fournaise Volcanological Observatory (OVPF-IPGP) in co-responsibility with the BRGM and its regional management in Mayotte. REVOSIMA relies on a close scientific and technical partnership with Ifremer and the CNRS.

The MD242 / MAYOBS25 campaign aims at establishing new bathymetric maps for monitoring the activity along with maintaining the different stations present on the seafloor (ocean bottom seismometers, hydrophones, pressure sensors) as well as in the water column, to monitor the evolution and/or changes in the seismic and eruptive activity, of the topography and fluid emissions, since the last monitoring campaigns MAYOBS23 (July 2023). MD242-MAYOBS25 also aims at acquiring geological samples to understand the current phenomenon.

A part of the MD242 / MAYOBS25 cruise is dedicated to maintain and retrieve the data of eight ocean bottom seismometers (6 OBS and 2 BB-OBS), two A-0-A pressure sensors, four hydrophones and one CIAM-instrument ( ADCP). Acoustic surveys in the water column and of the seafloor have also been carried out using multi-beam or single-beam echo sounders (EM122 and EK80). The following parameters (in brackets) are monitored as they provide crucial information regarding the evolution of the phenomenon and most particularly : the evolution acoustic plumes in the water column (SMF) and the topography (SMF, A-0-A), the seismicity (OBS, BB-OBS, Hydrophones), but also the currents in the water column (ADCP, CIAM). The physical or chemical anomalies associated with fluids emissions in the water column, previously identified using the EM122 and EK80 echo sounders, as well as with two gliders, were sampled using hydrocasts, sometimes with a glider to carry out inter-comparisons. During MD242-MAYOBS25, we also collected volcanic rock samples by dredging the seabed. Laboratory analysis of these samples will provide new information as for the past volcanic activity of the area.

REVOSIMA web portal [MAYOBS25]