An interdisciplinary approach to the pre-and syn-eruptive magma dynamics during the Tajogaite monogenetic eruption (La Palma, 2021)

Helena Albert^1,2*Pedro Antonio Torres-González³Héctor Lamolda^4,5Víctor Villasante-Marcos⁴Natividad Luengo-Oroz³Anselmo Fernández-García⁴Antonio Jesús Molina-Arias³Meritxell Aulinas^1,2Elena González-Alonso⁴Fernando Prieto⁴Guillem Gisbert^1,2Valentin R. Troll⁶

• ¹Universitat de Barcelona Departament de Mineralogia Petrologia i Geologia Aplicada, Barcelona, Spain
• ²Geomodels Research Institute, Universitat de Barcelona, Barcelona, Spain
• ³Instituto Geográfico Nacional, Centro Geofísico de Canarias, S/C de Tenerife, Spain
• ⁴Instituto Geografico Nacional Observatorio Geofisico Central, Madrid, Spain
• ⁵Research Group ‘Geodesia’, Universidad Complutense de Madrid, Madrid, Spain
• ⁶Department of Earth Sciences, Natural Resources & Sustainable Development (NRHU), Uppsala Universitet, Uppsala, Sweden

The 2021 Tajogaite eruption (La Palma, Canary Islands) provides a unique opportunity to investigate magma dynamics in magmatic systems where developed and monogenetic volcanoes coexist. Here, we present an integrated, interdisciplinary study combining petrological, geochemical, and geophysical data to reconstruct the pre-and syn-eruptive processes that controlled the evolution of the eruption. Whole-rock and mineral chemistry, diffusion chronometry in olivine crystals, gas geochemistry, GNSS, InSAR, seismicity and eruptive column height monitoring were jointly analyzed to constrain magma storage conditions, magmatic processes and the temporal evolution of the plumbing system. Our multidisciplinary results reveal a multi-stage magmatic history, involving at least three pre-eruptive intrusions (2017-2018, 2020, and in the weeks before the 2021 eruption) that progressively revived the system. Olivine diffusion modeling indicates that the 2021 eruption was triggered by a late-stage intrusion in early September, with ascent times of 10-30 days. Throughout the eruption, additional deep magma injections were recorded through changes in crystal chemistry, ground deformation, and eruptive dynamics. The earliest erupted magmas of the 2021 eruption were more evolved and hosted olivine crystals with oscillatory zoning, reflecting conduit opening and rapid ascent. During the second half of the eruption, the system transitioned to a regime marked by the development of a crystal mush zone, where magma accumulated without immediate eruption. This evolution was evidenced by prolonged olivine residence times and a characteristic five-day lag between deformation peaks and maximum eruptive column heights during this period. Therefore, to further improve eruption forecasting in monogenetic systems and to resolve the formation of transient magma storage zones in the upper crust that might control the eruption dynamics, we highlight the critical importance of integrating petrological and geophysical monitoring.