Magma Recharge and Reheating Driving the 2021-2023 Tephra Emissions of Villarrica Volcano, Southern Andes

Villarrica (Rukapillán) is the highest-threat volcano in Chile. For decades, persistent lava lake degassing within the crater has been interrupted by sporadic periods of unrest with increased Strombolian activity and tephra emission, leading to multiple transitions between different volcanic alert levels. Here, we analyse nine lapilli-to-bomb-sized pyroclasts emitted between December 2015 and September 2023 collected by local mountain guides at or near the crater after the cessation of different events of increased activity. In this work, we carried out textural and chemical analyses of whole rock, glass, mineral phases, and melt inclusions to understand the causes and evolution of the unrest periods after the latest March 2015 paroxysm. Findings reveal a shift in erupted compositions: basaltic products (~ 50–51 wt% SiO2) erupted between 2021 and 2023 contrast with basaltic andesites (52–56 wt% SiO2) erupted historically. Our estimates of magmatic intensive variables obtained on melt-only and mineral-melt pairs allow us to identify storage zones at < 5 kbar depth and magma temperatures between ~ 1020 and ~ 1110 °C. An overall cooling trend was interrupted by reheating in 2022, which we link to magmatic recharge. The most mafic products from November 2022 contain several low-An (56–64 mol.%) plagioclase phenocrysts that probably belong to more differentiated magma. Together with high-An (71–80 mol.%) sieve plagioclase phenocrysts and the lack of clinopyroxene, we suggest that a rejuvenation event (mafic magma recharge and reheating), possibly coupled with mush disaggregation, triggered the November 2022 activity. The results agree with geophysical precursors such as deformation and seismicity during this period. Magma rejuvenation processes mimic those observed during older historical eruptions at Villarrica. This study highlights the value of community-collected samples in improving understanding of the rhythms of Villarrica’s unrest episodes and how they allow for a more detailed inter-eruptive time resolution for understanding magmatic processes with implications for volcano monitoring and hazard assessment.