Birth of a large volcanic edifice through lithosphere-scale dyking offshore Mayotte (Indian Ocean)

Volcanic eruptions are foundational events that shape the Earth’s surface and provide a window into deep Earth processes. How the primary asthenospheric melts form, pond and ascend through the lithosphere is, however, still poorly understood. We document an on-going magmatic event offshore Mayotte Island (North Mozambique channel), associated with large surface displacements, very low frequency earthquakes and exceptionally deep (25-50 km) seismicity swarms. We present data from the May 2019 MAYOBS1 cruise, which reveal that this event gave birth to a 820m tall, ~ 5 km3 deep-sea volcanic edifice. This is the largest active submarine eruption ever documented. The data indicate that deep magma reservoirs were rapidly drained through dykes that intruded the entire lithosphere and that pre-existing subvertical faults in the mantle were reactivated beneath an ancient caldera structure. The new volcanic edifice is located at the tip of a 50 km-long volcanic ridge on the eastern insular slopes of Mayotte. The ridge is composed of many other recent edifices and lava flows and is an extensional feature that opens inside a wide transtensional boundary to transfer the strain between the East-African and Madagascar rifts. A hot asthenosphere at the base of a thick damaged lithosphere could be at the origin of this massive eruption.