The MAYOBS cruises are carried out to follow the evolution of the seismic and volcanic phenomenon which affects the island of Mayotte since May 2018 (REVOSIMA). They are carried out within the framework of an action program financed by the Ministry of Research, the Ministry of the Ecological and Solidarity Transition, the Ministry of Overseas with the support of the interministerial delegate of major risks in Overseas France and in liaison with other French ministries and institutes (IPGP, BRGM, IFREMER). The acquisition of geological and geophysical data is located east of Mayotte. Previous SHOM studies in the volcano area are also part of the MAYOBS project.

In the framework to the volcanological and sismological monitoring network of Mayotte (REVOSIMA), the new campaign, called MAYOBS17, was occured off the Mayotte island on board the R/V Pourquoi Pas? during 7-days in January-February 2021, (www.ipgp.fr/revosima). The MAYOBS17 campaign is integrated into the SISMAORE research campaign in order to benefit from the instruments present on board (MBES Reson, SDS, SISRAP). MAYOBS17 aims to establish new seabed maps to monitor seismic-volcanic activity in the investigation areas of previous MAYOBS campaigns. The objectives were to know whether the underwater volcanic phenomena detected during the 2019 and May 2020 campaigns (lava flows, volcanic fluids, etc.) have remained active and whether new phenomena have occurred since. The seabed is therefore scanned with the RESON Multbeam Echosounder, to carry out bathymetric maps, identify possible new volcanic flows and map the fluid emissions in the water column. These new acquisition will make it possible to follow the evolutions observed since October 2020 during MAYOBS15. Three mission chiefs led the campaign: Isabelle Thinon (BRGM) and Nathalie Feuillet (IPGP), on board the R/V Pourquoi Pas?, and Emmanuel Rinnert (IFREMER) on land.

During the first part of MAYOBS17 (January 17 to 21, 2021) the multibeam echosounder and water column acquisitions provided indicators of volcanic activity, including the evolution of the submarine relief and acoustic anomalies related to fluid emissions in the water column. Profiles of subbottom profilers (SBP), rapid 48-channel seismic reflection (SISRAP), magnetism and gravimetry were acquired. The second part of MAYOBS17 (January 24-25 and February 5-6, 2021) was dedicated to the relocation and recovery of the six Ocean Bottom Seismometers (OBS) as well as the recovery of the recorded data. These OBS are installed on the seabed up to 3500m water depth since MAYOBS15 (October 2020).

The magnetism and gravimetry data were also acquired. The second part of MAYOBS17 is dedicated to the relocation and recovery of the six Ocean Bottom Seismometers (OBS) as well as the recovery of the recorded data. These OBS were placed on the seabed (up to 3500m of water depth) during the MAYOBS15 campaign (October 2020).