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Variable genesis, storage, mingling, and decompression of andesitic magma in shallow reservoirs drive contrasting pyroclastic density currents at Volcán de Colima, Mexico

Rafael Torres-Orozco 1,2, Lucia Capra2, Víctor Márquez-Ramírez2, Giovanni Sosa-Ceballos3, Raphael De Plaen4, Héctor Cid2, Roberto Sulpizio5, Raúl Arámbula-Mendoza6

  • Affiliations: 1Centro de Ciencias de la Tierra, Universidad Veracruzana, Xalapa, Veracruz, Mexico; 2Instituto de Geociencias, Universidad Nacional Autonoma de Mexico, Juriquilla, Queretaro, Mexico; 3Instituto de Geofisica, Unidad Michoacan, Universidad Nacional Autonoma de Mexico, Morelia, Mexico; 4Royal Observatory of Belgium, Brussels, Belgium; 5Dipartimento di Scienze della Terra e Geoambientali, Universita degli Studi di Bari, Bari, Italia; 6Centro Universitario de Estudios e Investigaciones de Vulcanologia, Universidad de Colima, Colima, Mexico

  • Presentation type: Talk

  • Presentation time: Tuesday 15:45 - 16:00, Room S150

  • Programme No: 3.2.9

  • Theme 3 > Session 2

Abstract

The andesitic stratocone of Volcán de Colima experienced its last major explosive eruption in July 2015. This eruption began on July 10 with dome-collapse-driven block-and-ash flows, typical of Colima's recent activity, and was followed on July 11 by unprecedented open-vent, hot, scoria-rich pyroclastic density currents (PDCs) with a 10.5 km-runout. We conducted fieldwork, chemical analyses, and microtextural studies (electron-microscopy and x-ray microtomography) on the July 11 deposits to investigate the <20-hour transition between these events. Our results show that dome-collapse rapidly decompressed 1021°C, 2 wt.% H2O, and 58-59 wt.% SiO2 andesite at rates of 0.4-1.7 MPa/s from ~2 km-depth, driving magma fragmentation at strain rates of 10-3 s-1 and generating PDCs with discharge rates of 106-107 kg/s. Variations in decompression rates produced pulsating PDCs, reflecting heterogeneous andesite rheology influenced by multiple stages of magma genesis, ascent, storage, crystallization, and degassing. Additionally, the andesite mingled with rhyolitic melts from a mush layer at 2-5 km depths, a feature absent during prior large eruptions at Colima (1818 and 1913 Plinian events). Microtextural evidence, particularly well-preserved amphibole phenocryst nuclei from 10-15 km depth and the lack of inelastic strain in banded scoria clasts, suggests brief storage and efficient ascent through the shallow, amphibole-free mush. This mush likely tempered the eruption's explosivity in July 2015.