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

We report significant changes in the 3 He/ 4 He ratio measured at the Dos Aguas CO 2 ‐rich cold mineral spring (La Palma, Canary Islands) that represent early precursory signals of the 2021 Tajogaite eruption at Cumbre Vieja volcano. Air‐corrected 3 He/ 4 He ratio has an average value of 9.80 R A 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 3 He‐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 3 He‐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.