Decoding links between magmatic processes and eruption dynamics: whole-rock time series petrology of the 2021 Tajogaite eruption, La Palma

Abstract

We present an integrated petrological study of the 2021 Tajogaite eruption, La Palma, examining magmatic processes that initiated, sustained, and terminated surface volcanic activity. High temporal resolution sampling of near-continuously erupted alkali-basalt lava and tephra over the 85-day event reveals magma plumbing system dynamics from compositional trends. Initial deposits were mineralogically varied, reflecting mobilisation of shallow, evolved mush perturbed by fresh deep, primitive magma influx (Stage 1 - initiation). Transition to more primitive, uniform compositions recorded progressively deeper tapping of pre-existing magmatic zonation (Stage 2 - evacuation). The final stage (Stage 3 - waning) was characterised by more evolved magma compositions on the same fractionation trend as Stage 2, with tephra glass compositions suggesting a proportionately larger role of mush interstitial melts. We suggest this reflects shutdown of mantle-derived magma supply, a key process in eruption waning and termination, and compression-driven melt extraction of less mobile melts. Correlation with geophysical monitoring data demonstrates how near-real-time petrological monitoring could improve understanding of when an eruption may end.