Eruptive dynamics of open-vent andesitic volcanoes retrieved from petrological and componentry analysis of recent explosive phases (2020−2022) of Sangay (Ecuador)

Abstract

Since its reawakening in 2019, Sangay volcano (Ecuador) experienced a continuous, low magnitude eruptive activity that was disrupted by some mild-explosive pulses. Andean communities in central Ecuador and the Guayaquil International Airport have been affected by the ash fallouts. Through componentry, geochemical and petrological analysis, we studied ash and lapilli samples, emitted during the mild-explosive eruptions of 2020–2021 and during the minor eruptions of 2022, to document the changes in eruptive dynamics, constrain the pre-eruptive physical conditions, and identify the potential triggering mechanisms. Major elements whole-rock compositions show a progressive decrease in silica content, from andesitic to basaltic andesitic compositions, and a concomitant increase in magnesium content over time. Componentry, textures and chemical variations in groundmass glass support the idea that Sangay's shallow plumbing system hosts magmas that have evolved in composition, having variable physical properties that control the eruptive dynamics. The change in eruptive style towards more explosive dynamics in 2020–2021 was probably associated with the feeding of a more mafic and gas-rich magma from deep. The consequence, reflected in the groundmass glass chemistry and componentry data, is the “excavation” of the partially crystallized magma stalling in the conduits, which led to the observation of the more diverse compositions in the juvenile material. This work contributes to a better understanding of the eruptive behavior of long-lived, open-vent andesitic volcanoes, and to explore the link between eruptive dynamics and the petrological evolution of magmas.