Integrated constraints on explosive eruption intensification at Santiaguito dome complex, Guatemala

• Published in: Earth and planetary science letters Vol. 536; p. 116139
• Main Authors: Wallace, Paul A., Lamb, Oliver D., De Angelis, Silvio, Kendrick, Jackie E., Hornby, Adrian J., Díaz-Moreno, Alejandro, González, Pablo J., von Aulock, Felix W., Lamur, Anthony, Utley, James E.P., Rietbrock, Andreas, Chigna, Gustavo, Lavallée, Yan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.04.2020
• Subjects: effusive-explosive transitions; magma ascent; microlites; Santiaguito; seismicity; volcanic ash; volcanic ash; Santiaguito; effusive-explosive transitions; magma ascent; microlites; seismicity
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2020.116139

•Eruptive activity shifted to larger, irregular, ash-rich explosions in 2015–16.•The eruptive transition was assessed using a multi-parametric approach.•Activity was triggered by the injection of higher temperature magma from depth.•Microlite textures of eruptive products indicate contrasting magma ascent styles.•Explosions switched from low energy shear-driven to high energy overpressure-driven. Protracted volcanic eruptions may exhibit unanticipated intensifications in explosive behaviour and attendant hazards. Santiaguito dome complex, Guatemala, has been characterised by century-long effusion interspersed with frequent, small-to-moderate (<2 km high plumes) gas-and-ash explosions. During 2015–2016, explosions intensified generating hazardous ash-rich plumes (up to 7 km high) and pyroclastic flows. Here, we integrate petrological, geochemical and geophysical evidence to evaluate the causes of explosion intensification. Seismic and infrasound signals reveal progressively longer repose intervals between explosions and deeper fragmentation levels as the seismic energy of these events increased by up to four orders of magnitude. Evidence from geothermobarometry, bulk geochemistry and groundmass microlite textures reveal that the onset of large explosions was concordant with a relatively fast ascent of a deeper-sourced (∼17–24 km), higher temperature (∼960–1020°C) and relatively volatile-rich magma compared to the previous erupted lavas, which stalled at ∼2 km depth and mingled with the left-over mush that resided beneath the pre-2015 lava dome. We interpret that purging driven by the injection of this deep-sourced magma disrupted the long-term activity, driving a transition from low energy shallow shear-driven fragmentation, to high energy deeper overpressure-driven fragmentation that excavated significant portions of the conduit and intensified local volcanic hazards. Our findings demonstrate the value of multi-parametric approaches for understanding volcanic processes and the triggers for enigmatic shifts in eruption style, with the detection of vicissitudes in both monitoring signals and petrological signatures of the eruptive products proving paramount.