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, M. acknowledges support from the National Geographic grant number CP-122R-17 (Trail by Fire II-Closing the Ring project) and from IRD. We thank the CNES for the funding of geodesy work in Vanuatu through the TOSCA program "GEOV". We thank Université Nice Sophia Antipolis for funding the bathymetry processing through the CSI program "ARCHI-BATH". This project has also received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sk?odowska-Curie grant agreement No 665850