Horizon 1 1 17 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES Comptes Rendus Géoscience 195-223 MAYOTTE FANI MAORE 2023 fdi:010088394 ENG Comptes Rendus Géoscience 1631-0713 ISI:000929986500011 S2 10.5802/crgeos.155 https://www.documentation.ird.fr/hor/fdi:010088394 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2023-07/010088394.pdf 354 Horizon (IRD) The 'Fani Maoré' eruption off the coasts of Mayotte has been intensively monitored by applying methods similar to those used for subaerial eruptions. Repeated high-resolution bathymetric surveys and dredging, coupled with petrological analyses of time-constrained samples, allowed tracking the evolution of magma over the whole submarine eruptive sequence. Indeed, after one year of direct ascent (Phase 1), basanitic magma switched to a different pathway that sampled a tephri-phonolitic subcrustal reservoir (Phase 2). Later, the magma pathway shifted again in the crust resulting in a new eruption site located 6 km northwest of the main edifice (Phase 3). The petrological signature of lava flows reveals both an evolution by fractional crystallization and syn-eruptive mixing with a tephri-phonolitic magma. We demonstrate that high-flux eruption of large volumes of basanitic magma from a deep-seated reservoir can interact with shallower reservoirs and remobilize eruptible magma. This has significant hazards implications with respect to the capacity of such large eruptions to reactivate shallow-seated inactive reservoirs from a transcrustal magmatic system that could be located potentially at a distance from the high-flux eruptive site. 064 UR163