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

CANARY Islands; PALMA (Canary Islands)

We report significant changes in the 3He/4He ratio measured at the Dos Aguas CO2‐rich cold mineral spring (La Palma, Canary Islands) that represent early precursory signals of the 2021 Tajogaite eruption at Cumbre Vieja volcano. Air‐corrected 3He/4He ratio has an average value of 9.80 RA in the last 30 years (1991–2021). Helium isotope ratios higher than the average value were observed during the period 2008–2013 suggesting an input of 3He‐rich less‐degassed magma beneath La Palma lithosphere. Magma ascended in 2017–2018 toward another reservoir located beneath Cumbre Vieja at 10–15 km depth, causing detectable seismic swarms located between 15 and 25 km, followed in 2020 by additional inputs of 3He‐rich less‐degassed magma that intruded at depth. Finally, in 2021 the buoyancy of magma and the pressure of the exsolved gases overcame the lithospheric resistance and a volcanic eruption took place between 19 September and 13 December 2021. Plain Language Summary: In this work we report how measurements of helium, released from the mantle of the Earth and present in the bubbling gases of a CO2‐rich cold mineral spring, showed the earliest geochemical precursory signals of the 2021 Tajogaite eruption that took place at Cumbre Vieja volcano, La Palma Island (Canary Islands). According to our data, magma began to rise from deep sources of the mantle in the period 2008–2013 and other important inputs took place in 2020. Key Points: The primordial component of the Canary mantle source is feeding the gases released at Dos Aguas CO2‐rich cold mineral springThe Tajogaite eruption of 19 September–13 December 2021 at Cumbre Vieja volcano, was preceded by significant changes in the 3He/4He ratioThe magmatic reactivation started in the period 2008–2013, when an input of less‐degassed magma rose to shallower lithospheric depths beneath La Palma [ABSTRACT FROM AUTHOR]

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