These’s title : From magma ascent to deep-seated-ocean lava flow emplacement: the case study of the ongoing (since 2018) submarine eruption offshore Mayotte
Following the seismic crisis that has been impacting Mayotte Island (Western Indian Ocean) since May 2018, a lithosphere-scale magmatic event gave birth to a 820-m high submarine volcano 50 km from the island, and produced about 6.4 km3 of magma on the ocean floor at 3,300 m depth. Studying volcanism in a deep submarine environment is a real challenge. However, since May 2019, several scientific cruises, led by the French scientific community, have collected a large number of samples (obtained by sea floor dredges) and time-series of bathymetric data through the 2018-2021 period. Samples from the flank of the active volcano, and from distal ponded lava, lava domes and currently active distal fractures, give us a unique dataset to track the spatial and temporal variations in lava effusive rate, facies and syn-eruptive degassing.
The goal of the PhD project is to provide a complete picture of the volcanic system, integrating pre-eruptive conditions of the deep-seated mantle reservoir, magma ascent and degassing/cooling- induced vesiculation and crystallization along the conduit, and magma emplacement on the ocean floor.
- Quantitative textural analysis of the samples to quantify (i) degassing variations in time and space, (ii) magma ascent time and velocity, and (iii) physical properties/parameters of the erupted material that control the ascent dynamics and submarine emplacement.
- These textural analyses will be integrated with experimental petrology and volcanology measurements to (i) constrain the degassing evolution of the magma towards the surface, (ii) determine the link between decompression rate and vesicle and crystal number densities in mafic magmas, (iii) establish the temperature dependence of viscosity for these compositions (basanite to phonolite), and (iv) quantify the effect of crystal and bubble growth on viscosity during ascent and submarine lava emplacement.
- Finally, bathymetry of the growing volcano and lava flow morphology will be examined to (i) correlate sample texture to lava flow morphology, (ii) relate lava flow morphology diversity to effusion rate variation, and iii) constrain submarine lava flow emplacement dynamics (duration, advance rates, effusion rates).
- Oryaëlle Chevrel
- Lucia Gurioli
- Etienne Médard
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