Voluminous Storage and Rapid Magma Ascent Beneath La Palma Revealed by Seismic Tomography

Abstract

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.

Early Precursory Changes in the 3He/4He Ratio Prior to the 2021 Tajogaite Eruption at Cumbre Vieja Volcano, La Palma, Canary Islands

“…The occurrence of the seismic swarms in 2017 and 2018 suggests the buoyancy of magma pockets stagnated in 2008–2013 toward another reservoir located beneath Cumbre Vieja at 12–15 km depth (second episode in Figure 5) that was previously present in the form of a large sub‐crustal magma‐filled rock volume intrusion, according to the recent observations reported by D’Auria et al. (2022). Together with the seismic swarms of October 2017 and February 2018, a relevant deformation detected by De Luca et al.…”

“…Finally, in 2021 the buoyancy of magma and the pressure of the exsolved gases overcame the lithospheric resistance and the eruption took place, after a precursory seismicity that began eight days before the eruption (D’Auria et al., 2022), with an evident upward migration of hypocenters as can be observed in Figure 4. During the eruption, the seismicity was mainly concentrated at a subcrustal (10–15 km) and an upper mantle (20–25) depth (D’Auria et al., 2022), but the feeding of other 3 He‐rich magma from lower sources was unlikely due to the observed decline in the primitive‐type He since the end of 2020 until the eruptive period (Figure 3b). In summary, 3 He/ 4 He ratio data pointed to two different episodes of magmatic gas exolution likely due to magma rise in 2008–2013 and 2020.…”

“… Temporal evolution of the observed changes in the air‐corrected 3 He/ 4 He ratio measured in DA (red squares) and hypocentral depth of the seismic activity located in the period 1 January 2017–16 December 2022 (gray circles, D’Auria et al., 2022). The yellow area represents the eruptive period.…”

“…The volcanic edifice created and the subaerial deposit of lava flows and proximal fallout have a volume estimated in 217.4 ± 6.6 Mm 3 (Civico et al., 2022). Geophysical precursory signals of the 2021 eruptive process took place on 7–13 October 2017, when a remarkable seismic swarm interrupted a seismic silence of 50 years, with earthquakes located beneath Cumbre Vieja volcano at depths ranging between 15 and 25 km with a maximum magnitude of 2.7 (D’Auria et al., 2022). Geochemical precursory signals were also observed before and during 2017 in the form of significant increases in the diffuse He and H 2 degassing throughout the entire Cumbre Vieja building (Padrón et al., 2018; Pérez et al., 2018).…”

“…Geochemical precursory signals were also observed before and during 2017 in the form of significant increases in the diffuse He and H 2 degassing throughout the entire Cumbre Vieja building (Padrón et al., 2018; Pérez et al., 2018). Such observations were explained to be caused by an upward magma migration from an ephemeral magmatic reservoir, located in the upper mantle (about 25 km depth), toward another reservoir located close to the Moho beneath Cumbre Vieja (12–15 km) (Pérez et al., 2018; D’Auria et al., 2022). Additional seismic swarms were registered in 2018 (1), 2020 (5, one of them a seismic swarm of LP events) and 2021 (2), before the seismic series that preceded the eruption, beginning a week before it (D’Auria et al., 2022).…”