Abstract
Volcanic eruptions shape 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. Since 10 May 2018, magmatic activity has occurred offshore eastern Mayotte (North Mozambique channel), associated with large surface displacements, very-low-frequency earthquakes and exceptionally deep earthquake swarms. Here we present geophysical and marine data from the MAYOBS1 cruise, which reveal that by May 2019, this activity formed an 820-m-tall, ~5 km³ volcanic edifice on the seafloor. This is the largest active submarine eruption ever documented. Seismic and deformation data indicate that deep (>55 km depth) 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. We locate the new volcanic edifice at the tip of a 50-km-long ridge composed of many other recent edifices and lava flows. This volcanic ridge is an extensional feature inside a wide transtensional boundary that transfers strain between the East African and Madagascar rifts. We propose that the massive eruption originated from hot asthenosphere at the base of a thick, old, damaged lithosphere.
Highlights
Volcanic eruptions are foundational events that shape the Earth’s surface and provide a window into deep Earth processes
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
Summary
The French national research program “SISMAYOTTE” was launched in February 2019 to determine the origin of the seismicity and deformation, to search for any seafloor volcanic activity and to understand the scale, chronology and implications of the crisis. As part of this program, we 1) set up seismic and Global Navigation Satellite System (GNSS) stations on Mayotte and Grande Glorieuses Islands, 2) deployed Ocean Bottom Seismometers (OBS). The NVE was detected by comparing our data to those acquired during a 2014 survey by the French Naval Hydrographic and Oceanographic Service (SHOM) (Figure 2a). The edifice sits on an area that, in the seafloor topography, was locally almost flat at around 3300 m below sea level (bsl)
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