The c.2030 yr BP Plinian eruption of El Misti volcano, Peru: Eruption dynamics and hazard implications Gisela Cobeñas a, ⁎, Jean-Claude Thouret a , Costanza Bonadonna b , Pierre Boivin a a PRES Clermont, Université Blaise Pascal, Laboratoire Magmas et Volcans, CNRS, UMR6524 and IRD R-163, F-63038 Clermont-Ferrand Cedex, France b Earth and Environmental Sciences Section, University of Geneva, 13 Rue des Maraîchers, Geneva, CH 1205 Switzerland abstract article info Article history: Received 1 November 2011 Accepted 3 June 2012 Available online 15 June 2012 Keywords: Tephra deposit Pyroclastic density currents El Misti Eruptive parameters Volume Hazard ‘El Misti’ volcano near the city of Arequipa in south Peru produced a Plinian eruption c.2030 yr BP that resulted in a tephra deposit consisting of three fallout layers, several pyroclastic density current (PDC) de- posits, a late stage, small debris-avalanche deposit, and lahar deposits. This VEI 4 Plinian eruption of El Misti has been selected as one of the reference eruptions for the hazard assessment and risk mitigation plan for the city of Arequipa. The Plinian column of this eruption rose up to 21–24 km and produced a tephra deposit over an area of at least 2580 km 2 within the 5 cm-isopach line. The dispersal axis is oriented SW, i.e. towards the area of the basin and city of Arequipa. Later pumice- and lithic-rich PDC deposits were emplaced into radial valleys extending from the volcano up to a distance of at least 13 km. The eruption produced a minimum total bulk volume of 1.2 km 3 (0.71 km 3 DRE volume) of tephra and PDC deposits. Components of the tephra de- posit consist of beige, gray and banded pumices, lithic fragments, a minor amount of cogenetic dacite clasts, and free crystals. The minimum volume of the tephra deposit varies between 0.2 and 0.6 km 3 (exponential, power-law integration and inversion of TEPHRA2 analytical model). The tephra deposit is characterized by a bulk density of 1500 kg/m 3 which results in a mass of 2.5–9.0 × 10 11 kg. The maximum mass discharge rate (MDR) is 1.1 × 10 8 kg/s based on a plume height of 24 km. The estimated duration of the Plinian eruption ranges between 0.6 and 2.3 h. Grain size distribution, componentry, and SEM analyses of both the tephra and PDC deposits, combined with the reconstructed stratigraphic sequence of the deposit, suggest that the eruption took place in five stages: (1) generation of a 21–24 km-high eruptive column that deposited the lower tephra layer; (2) collapse of the crater walls and partial obstruction of the vent during a period of decreased intensity, which led to the formation of a thin sand-sized, lithic-rich, middle tephra layer; (3) resurgence of a Plinian eruption column that formed the upper tephra layer; (4) subsequent collapse of the column that produced the PDC deposits; and (5) failure of the hydrothermally altered part of the crater rim towards the S and SE that resulted in a coarse, lithic-rich debris-avalanche deposit. Geochemical and mineralogical data obtained from the banded pumices suggest a mechanical mixing between two magma batches of dacite (~70% SiO 2 ) and andesite (61.7–64.1% SiO 2 ) prior to eruption. The abundance of altered lithics in the uppermost tephra layer suggests that the hydrothermal system operating in the summit area of the volcano was partially disrupted and the vent enlarged just before the transition to the collapse of the column. © 2012 Published by Elsevier B.V. 1. Introduction El Misti volcano (5822 masl), located in southern Peru within the northern segment of the Central Andes volcanic zone, is potentially one of the most active volcanoes in the region (Fig. 1; De Silva and Francis, 1991; Thouret et al., 2001; Legros, 2001; Delaite et al., 2005; Vargas Franco et al., 2010). Arequipa is the second city and economic center of Peru with a population of ~1 million and is located at the foot of El Misti. The city center lies only 17 km southwest of El Misti's crater at an elevation of 2325 m (approximately 3500 m lower than the volcano summit). In the past, El Misti has displayed a wide variety of eruptive styles, including numerous Vulcanian and several Plinian eruptions. From these, two eruptions have been selected as reference scenarios by the scientific committee advising the Peruvian Civil Protec- tion Agency for emergency and prevention planning. The small magni- tude (high frequency) Vulcanian eruption that occurred in AD 1440– 1450 (VEI 2) has been selected as the most probable scenario in case of El Misti's reawakening. This is the last magmatic eruption that oc- curred at El Misti and the present summit vent is now occupied by an andesitic plug. The c.2030 yr BP eruption has been selected as the Journal of Volcanology and Geothermal Research 241–242 (2012) 105–120 ⁎ Corresponding author at: School of Earth Sciences, University of Tasmania, Hobart, Australia. Tel.: + 61 3 62262478. E-mail address: gcobenas@utas.edu.au (G. Cobeñas). 0377-0273/$ – see front matter © 2012 Published by Elsevier B.V. doi:10.1016/j.jvolgeores.2012.06.006 Contents lists available at SciVerse ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores