For the first time, we obtained high-resolution images of Earth's interior of the La Palma volcanic eruption that occurred in 2021 derived during the eruptive process. We present evidence of a rapid magmatic rise from the base of the oceanic crust under the island to produce an eruption that was active for 85 days. This eruption is interpreted as a very accelerated and energetic process. We used data from 11,349 earthquakes to perform travel-time seismic tomography. We present high-precision earthquake relocations and 3D distributions of P and S-wave velocities highlighting the geometry of magma sources. We identified three distinct structures: (1) a shallow localised region (< 3 km) of hydrothermal alteration; (2) spatially extensive, consolidated, oceanic crust extending to 10 km depth and; (3) a large sub-crustal magma-filled rock volume intrusion extending from 7 to 25 km depth. Our results suggest that this large magma reservoir feeds the La Palma eruption continuously. Prior to eruption onset, magma ascended from 10 km depth to the surface in less than 7 days. In the upper 3 km, melt migration is along the western contact between consolidated oceanic crust and altered hydrothermal material.

Seismic tomography provides a window into magmatic plumbing systems; however, obtaining sufficient data for ‘real-time’ imaging is challenging. Until now, syn-eruptive tomography has not been successfully demonstrated. For the first time, we obtained high-resolution images of Earth's interior during an ongoing volcanic eruption. We used data from 11,349 earthquakes, most of which during La Palma eruption (19 September-13 December, 2021), to perform travel-time seismic tomography. We present high-precision earthquake relocations and 3D distributions of P and S-wave velocities highlighting the geometry of magma sources. We identified three distinct structures: (1) a shallow localised region (< 3 km) of hydrothermal alteration; (2) spatially extensive, consolidated, oceanic crust extending to ~10 km depth and; (3) a large (> 400 km3) sub-crustal magma-filled rock volume intrusion extending from ~7 to 25 km depth. Our results suggest that this large magma reservoir feeds the La Palma eruption continuously for almost three months. Prior to eruption onset, magma ascended from ~10 km depth to the surface in < 7 days. In the upper 3 km, melt migration is along the western contact between consolidated oceanic crust and altered hydrothermal material. Similar structural weaknesses along the eastern contact could potentially cause new eruptive centres in the future.

La Palma island is located in the NW of the Canary Islands and is one of the most volcanically active of the archipelago, therefore the existence of geothermal resources on the island is highly probable. The main objective of this work is to detect velocity anomalies potentially related to active geothermal reservoirs on La Palma island, by achieving a high-resolution seismic velocity model of the first few kilometres of the crust using Ambient Noise Tomography (ANT). The obtained ANT model is merged with a recent local earthquake tomography model. Our findings reveal two high-velocity zones in the island’s northern and southern parts, that could be related to a plutonic intrusion and old oceanic crust materials. Conversely, four low-velocity zones are imaged in the southern part of the island. Two of them can be related to hydrothermal alteration zones located beneath the Cumbre Vieja volcanic complex. This hypothesis is reinforced by comparing the S-wave velocity model with the seismicity recorded during the pre-eruptive phase of the 2021 Tajogaite eruption, which revealed an aseismic volume coinciding with these low-velocity zones. Another low-velocity zone is observed in the southern part of the island, which we interpret as highly fractured rocks which could favour the ascent of hot fluids. A last low-velocity zone is observed in the central part of the island and associated with loose deposits generated by the Aridane valley mega landslide.

On Sept. 19th, 2021, a volcanic eruption began on the island of La Palma (Canary Islands, Spain). The pre-eruptive episode was characterized by seismicity and ground deformation that started only 9.5 days before the eruption. In this study, we applied seismic interferometry to the data recorded by six broadband seismic stations, allowing us to estimate velocity variations during the weeks preceding the eruption. About 9.5 days before the eruption, we observed a reduction in the seismic velocities is registered next to the eruptive centers that opened later. Furthermore, this zone overlaps with the epicenters of a cluster of volcano-tectonic earthquakes located at shallow depth (< 4 km) and detached from the main cluster of deeper seismicity. We interpret the decrease in seismic velocities and the occurrence of such a shallow earthquake cluster as the effect of hydrothermal fluid released by the ascending magma batch and reaching the surface faster than the magma itself.