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Study underwater lava flows by combining bathymetry and hydro-acoustic signals

On the ocean floor, the meeting of lava and water during volcanic eruptions generates acoustic signals that propagate into the ocean. Lava flows are also revealed by bathymetric differentials recorded during oceanographic campaigns. In Mayotte, a study led by IPGP scientists shows how the two techniques work together to give a detailed picture in time and space of the evolution of lava flows at great depths (3000 m).

Study underwater lava flows by combining bathymetry and hydro-acoustic signals

Publication date: 07/11/2022

General public, Observatories, Press, Research

Related teams :
Volcanic Systems

The major limitation in the study of submarine volcanoes is their difficulty of access. However, detailed reconstruction of the evolution of eruptions in these magmatic systems is an important challenge if we are to gain a better understanding of submarine volcanic eruptions, the relationship between manifestations on the seabed and deep-sea signals (seismicity, deformation, degassing) and better anticipate future eruptions.

OBS deployment sites off Mayotte during the October 2020 campaign.

Since May 2018, intense volcanic activity has been occurring 50 km east of the coast of Mayotte at a depth of more than 3,000 m. In 4 years, more than 6 km3 of lava have been extruded onto the seabed, forming the 800 m high Mount Fani Maoré in less than a year. This exceptional activity generates numerous observables that are studied through the Mayotte volcanological and seismological monitoring network (REVOSIMA), a structure operated by the IPGP, in charge of monitoring volcanic and seismic activity in the Mayotte region since 2019.

To refine our knowledge of this activity, a group of scientists from the IPGP, in particular the OVPF, and Ifremer exploited several types of data acquired during a 10-day oceanographic campaign in October 2020. In a study published on October 5th in the journal Frontiers in Earth Science, they were able to highlight the complementary nature of two methods: the analysis of hydro-acoustic signals and bathymetry differentials. Using a thousand events that generated manually identified hydro-acoustic signals and 6 bathymetric surveys of the seabed carried out over the same period, they were able to reconstruct the morphology of the lava flows and their evolution, increasing the accuracy of the study compared with each of the methods used individually. The bathymetric differentials enable the eruption zone to be positioned very precisely. Then, the evolution of the positions of the hydro-acoustic signals shows the temporal evolutions on a very fine time scale and confirms the observation of slight bathymetric variations.

The combination of the two methods offers new opportunities for understanding the day-to-day evolution of lava flows. This methodology, applied to the data recorded since 2019, will enable a more detailed reconstruction of the eruption and the evolution of lava flows in the Fani Maoré region, off Mayotte. Finally, this demonstration will make it possible to envisage the operational use of the detection and processing of hydro-acoustic signals to monitor eruptive activity on the seabed.

Ref: Saurel Jean-Marie, Retailleau Lise, Deplus Christine, Loubrieu Benoît, Pierre Delphine, Frangieh Michel, Khelifi Nassim, Bonnet Robin, Ferrazzini Valérie, Bazin Sara, Guyavarch Pierre, Moulin Maryline, REVOSIMA Seismology group , REVOSIMA Bathymetry group, Combining hydro-acoustic sources and bathymetric differences to track the vent evolution of the Mayotte eruption, Mozambique Channel, Frontiers in Earth Science, 2022, DOI : 10. 3389/feart.2022.983051

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