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Eruptive dynamics during open-vent andesitic eruptions retrieved from petrological and componentry analysis of Sangay volcano (Ecuador)

1Nicole Vizuete, 1Pablo Samaniego, 2Benjamin Bernard, 1Jean-Luc Devidal, 3Diego F. Narváez, 4Céline Liorzou, 2Silvana Hidalgo

  • Affiliations: 1Laboratoire Magmas et Volcans, Université Clermont Auvergne-CNRS-IRD, Clermont-Ferrand, France; 2Instituto Geofísico, Escuela Politécnica Nacional, Ladron de Guevara E11-253, Quito, Ecuador; 3Departamento de Geología, Escuela Politécnica Nacional, Ladron de Guevara E11-253, Quito, Ecuador; 4Université de Bretagne Occidentale, Géosciences Océan IUEM, 29280 Plouzané, France

  • Presentation type: Talk

  • Presentation time: Tuesday 10:45 - 11:00, Room S150

  • Programme No: 3.2.2

  • Theme 3 > Session 2

Abstract

Constraining the pre-eruptive physical conditions and changes in eruptive dynamics at open-vent volcanoes is a key step of any hazard assessment initiative. Sangay volcano in Ecuador is an active, open-vent andesitic system that exhibited intense eruptive activity since 2019. This activity is characterized by recurrent low- to moderate explosivity eruptions, whose ash fallouts impacted communities across south-central and west-central Ecuador. This study analyzes ash and vesiculated lapilli samples from explosive eruptions between 2020 and 2022 to better understand transitions in eruptive dynamics. Variations in componentry, particle textures and chemical compositions indicate shifts in magma dynamics from Strombolian to violent Strombolian, with progressive sealing of the conduit, triggering larger explosive pulses (e.g., 20 September 2020, 5--6 March 2021). These events involved lateral conduit excavation, transporting accidental, and juvenile components. Subsequent pulses (11 March--7 May 2021) were driven by decompression and hotter gas-rich magmatic recharge, resulting in the fragmentation of low-viscosity magma. Whole-rock geochemical data from 2019--2022 reveal andesitic to basaltic andesitic compositions (56--61 wt.% SiO₂), with an invariable mineral assemblage composed of pl + ol + cpx + opx and Fe-Ti oxides. Geochemical modeling suggests fractional crystallization in a shallow reservoir and thermobarometry analysis places the magmatic system at 10--14 km depth (270--400 MPa). Pre-eruptive conditions include magma temperatures of 1029--1077°C and water contents of 1--2 wt.%. This study enhances our understanding of the eruptive processes of open-vent andesitic volcanoes by linking changes in eruptive dynamics to the petrological evolution of magma.