PRIMER BOLETÍN VOLCANOLÓGICO CHILENO 2019

Miembros Dra. Inés Rodríguez Araneda- Universidad Católica de Temuco Dr. (c) Jorge Romero Moyano–University of Manchester Sr. Franco Vera Rivadeneira - Servicio Nacional de Geología y Minería Sr. Nicolás Luengo Vásquez – Universidad de Concepción Srta. Constanza Perales Moya – Universidad de Concepción Dr. (c) Gabriel Orozco Lanfranco- Universidad de Concepción Srta. Verónica Valdés Velásquez- Universidad Andrés Bello

INTRODUCCIÓN

El grupo Volcanología Chile está conformado por geólogas y geólogos, que están desarrollando trabajos de investigación en algunos de los volcanes activos en nuestro país. Mediante esta iniciativa, sin fines de lucro, se busca acercar a la comunidad nacional a través de la divulgación de contenidos científicos sobre volcanes, con el fin de incrementar el conocimiento de la sociedad sobre este tipo de fenómenos geodinámicos. Entre nuestros objetivos está la creación de una red de colaboradores especialistas en volcanes a nivel nacional, entre los cuales exista un flujo constante de información académica vanguardista, que permita mantener a la ciudadanía informada sobre los últimos avances en volcanología.

El objetivo de este boletín es difundir y entregar a la comunidad, de todos los ámbitos, los trabajos científicos de investigadores chilenos y extranjeros, en lo que compete a las geociencias en el área de la volcanología en Chile.

Solicitamos a los investigadores nacionales e internacionales que se encuentran trabajando en volcanes Chilenos y que publican sus resultados en revistas indexadas durante 2019, comunicarse con nosotros para considerarlos en la próxima edición de este boletín. Así mismo, invitamos a estudiantes de pregrado a enviar información equivalente respectiva a sus tesis o memorias de pregrado que se encuentren aprobadas.

Contacto:

[email protected]

Eruptive sequence and seismic activity of Llaima volcano (Chile) during the 2007–2009 eruptive period: Inferences of the magmatic feeding system

Luis Francoa,b,⁎,José Luis Palmab,c, Luis E. Larad,e, Fernando Gil-Cruza, Carlos Cardonaa, Daniel Basualtof, Juan San Martíng a Observatorio Volcanológico de los Andes del Sur, Servicio Nacional de Geología y Minería, Rudecindo Ortega 03850, Temuco, Chile b Programa de Doctorado en Ciencias Geológicas, Universidad de Concepción, Víctor Lamas 1290, Concepción, Chile c Departamento de Ciencias de la Tierra, Facultad de Ciencias Químicas, Universidad de Concepción, Víctor Lamas 1290, Concepción, Chile d Servicio Nacional de Geología y Minería, Av. Santa María 0104, Santiago, Chile. Research Center for Integrated Risk Management (CIGIDEN), Av. Vicuña Mackenna 4860, Santiago, Chile f Departamento de Geología y Obras Civiles, Facultad de Ingeniería, Universidad Católica de Temuco, Chile g Departamento de Ciencias Físicas, Facultad de Ingeniería, Universidad de la Frontera, Casilla 54-D, Temuco, Chile

Abstract Llaima April Volcano, one of the most active volcanoes in South America, has experienced intense activity during the last 100 years. The most recent eruptive activity occurred during the period 2007–2009 with at least six energetic eruptions, the January 1st 2008 (VEI 3) being the strongest episode. Most of the paroxysmal activity was characterized by a rapid increase in seismic energy (minutes to hours) and the absence of precursory signals, as well as by an accelerated drop of the seismic energy and eruption intensity at the end. Moreover, subtle changes in the increase of low-energy long-period (LP) seismicity and the occurrence of minor explosive activity (six months before the onset of the eruptive cycle), were the only remarkable changes observed in advance. This is the first study that includes a detailed description of the 2007–2009 eruptive period and is based on a temporal analysis of the seismic records, technical reports from the monitoring network andN2000 photos. This set allows a characterization of the coeval eruptive styles (including strombolian and hawaiian activity), morphological changes of the active vents inside the main crater and two fractures located in the SW and SE flanks. Ten phases were identified based on the eruptive style, Volcanic Explosivity Index (VEI) and the salient features of the seismic events. The seismicity that accompanied the eruptive phases was characterized by the predominance of a continuous tremor (TR) and discrete LP events, and a remarkable absence of volcano- tectonics (VT) earthquakes. A waveform cross-correlation analysis of LP events showed an overall low similarity between them, which suggests multiple sources. Our observations and analysis suggest that the plumbing system is composed of multiple independent structures, some of which reached the surface during this eruptive period, indicating that the upper part of the cone could be an unstable and essentially weak zone. The activity and seismicity observed are characteristic of an open-vent system in which the magma can ascend rapidly from several km depth, with little to no clear precursory activity. These results are in agreement with petrological studies of the products of these eruptions.

⁎Corresponding author at: Observatorio Volcanológico de los Andes del Sur, Servicio Nacional de Geología y Minería, Rudecindo Ortega 03850, Temuco, Chile. E-mail address: [email protected] https://doi.org/10.1016/j.jvolgeores.2019.04.014

Numerical wave propagation study of the unusual response of Nevados de

Chillán volcano to two aftershocks of the 2010 MW= 8.8 Maule earthquake

Cristian Faríasa,c∗, Boris Galvánb a Departamento de Geología y Obras Civiles, Facultad de Ingeniería, Universidad Católica de Temuco, Temuco, Chile b The Centre for Hydrogeology and Geothermics, University of Neuchatel, Neuchatel, Switzerland c GeoKimün, Centro de Investigación en evaluación de riesgos y mitigación de procesos geológicos, Universidad Católica de Temuco.

Abstract

In 2012, two large aftershocks of the MW= 8.8 Maule, Chile earthquake occurred near the Central Chilean coast. Both events, with magnitudes MW= 6.1 and MW= 7.1 were located about 200 km away from the volcanic/hydrothermal Nevados de Chillán (NdC) complex. The system responded with a significant increase in seismicity to the MW= 6.1 event, and with a reduction in seismicity following the latter, larger MW= 7.1 earthquake. To understand the physical changes induced by both earthquakes at the NdC, we set up a numerical wave propagation study. Our results show that these observations likely result from dynamic changes at the NdC complex during the passage of the seismic waves. In the case of the MW= 6.1 aftershock, the extensive stress transfer was large enough to induce changes at the hydrothermal system, which could have later led to an increase in fluid-driven seismicity. In the case of the MW= 7.1 earthquake, the oblique arrival of seismic waves to the main fault of the NdC due to the MW= 7.1 earthquake induced slight compressions at the reservoir and created openings in the main fault, promoting fluid migration, which can explain the reduction in seismicity beneath the main craters of the volcano. Results also show that the geometry of an underlying fault system can influence the volumetric response, suggesting that the role of local structures in earthquake-volcano interactions influence the behavior of triggered systems and should therefore not be disregarded.

∗Corresponding author Email address: [email protected]

Pyroclastic deposits and eruptive heterogeneity of Volcan Antuco (37°S; Southern Andes) during the Mid to Late Holocene (<7.2 ka)

Jorge E. Romeroa,⁎, Victoria Ramireza, Mohammad Ayaz Alama, Jorge Bustillosb, Alicia Guevarac, Roberto Urrutiad, Alessandro Piselloe, Daniele Morgavie, Evelyn Criolloc a Departamento de Geología, Facultad de Ingeniería, Universidad de Atacama, Avenida Copayapu 485, Copiapó, Chile b Carrera de Ingeniería en Geología, Facultad de Ingeniería en Geología, Minas, Petróleos y Ambiental, Universidad Central de Ecuador, Quito, Ecuador c Departamento de Metalurgia Extractiva Escuela Politécnica Nacional, Quito, Ecuador d Centro de Ciencias Ambientales (EULA), Universidad de Concepción, Concepción, Chile e Department of Physics and Geology, University of Perugia, Piazza dell’ Università, 06123 Perugia, Italy

A b s t r a c t Volcan Antuco (37°24′ S, 71°22′W; 2979 m asl) is the 13th ranked high threat volcano in Chile with 27 recorded historical eruptions, mostly (~96%) with volcanic explosivity indices (VEI) of ~1–2. An older eruptive record has been reconstructed from sections exposed on the western flank and is intimately related to a well-documented catastrophic sector collapse at ~7.2 cal ka BP. However, very little is known about Antuco's post-collapse eruptive history in other sectors, especially on the eastern flanks where prevalent westerly winds favor optimal eastward tephra transport and deposition. Our study reveals a more complete record of activity that has already been indicated from previous work with at least 23 tephra-forming explosive eruptions, most of them within the last c. 7.2 ka, including 4 events that have generated pyroclastic density currents that have widely inundated the lower eastern flanks. Tephra from these eruptive events are typically composed of scoria, free crystals and lithics, with occasional pumice. The composition of juvenile fragments varies between basalt and trachyandesite (50.2–62.2 wt% SiO2) and show phenocrysts of plagioclase, olivine and pyroxene. Our results show that most of the eruptions of Antuco (c. 79%) are Strombolian to violent Strombolian. These eruptions have an estimated longer repose times (c. 200 year) and are likely higher in magnitude than those registered during historical times. This study also shows that the composition, style and magnitude may change from one eruptive episode to the next. This eruptive variability seems in complete accord with recent findings from other centers in the Southern Volcanic Zone exhibiting similar temporal eruptive diversity and ultimately, has significant implications with respect to hazard assessment.

⁎ Corresponding author. E-mail address: [email protected] (J.E. Romero) https://doi.org/10.1016/j.jvolgeores.2019.1067590377-0273/c 2019.

Linking the mafic volcanism with the magmatic stages during the last 1 Ma in the main volcanic arc of the Altiplano-Puna Volcanic Complex (Central Andes)

Benigno Godoya, Marco Taussib, Osvaldo González-Maurelcd, AlbertoRenzullib, Loreto Hernández- Prata, Petrus le Rouxd, Diego Morataa, Andrew Menziese a Centro de Excelencia en Geotermia de los Andes (CEGA) y Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile b Dipartimento di Scienze Pure e Applicate, Università degli Studi di Urbino Carlo Bo, Via Ca' le Suore, 2/4, 61029 Urbino, Italy c Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avda. Angamos, 0610, Antofagasta, Chile d Department of Geological Sciences, University of Cape Town, Rondebosch 7700, South Africa e Bruker Nano GmbH, Am Studio 2D, Berlin 12489, Germany

Abstract

The Altiplano-Puna Volcanic Complex is a province of the Central Andes mainly associated, since the Miocene (26 Ma), with the eruption of voluminous silicic magmas (>65 wt % SiO2). The result of these eruptions is an extensive ignimbritic plateau which covers an area >50,000 km2. Major eruptions (i.e. flare-up events) of these magmas occurred with a cyclic periodicity, on which each cycle last 2–3 Ma, and steady-state and/or waning periods occurred between each cycle. After the last flare-up cycle of evolution of the Altiplano-Puna Volcanic Complex (ended at ca.1 Ma), low to intermediate silica (<59 wt % SiO2; commonly referred as “mafic”) extrusive products have erupted in a scattered way throughout the magmatic province. This mafic volcanism is exposed mainly as monogenetic centers (scoria cones or maar-like structures), isolated flows, or as part of more differentiated stratovolcano complexes (e.g., San Pedro, Sairecabur, Licancabur, and Lascar). The origin of these mafic products has been related to partial melting of the mantle wedge and an evolution affected by the presence of different MASH-type zones at lower (>40 km depth) and upper (<40 km depth) crustal levels, with limited low-pressure fractional crystallization. Nevertheless, dacitic magma chambers (4–8 km depth) may have benefited from mafic magma inputs to be remobilized and erupted as silicic domes <0.2 Ma (e.g. Chao Dacite). In fact, widespread enclaves hosted in these young domes represent a snapshot of the pre- eruptive magma mingling-mixing processes at the dacite-mafic interface. We are going to deal with the mafic magmas erupted after the last major flare-up ignimbritic phase - i.e. during the last 1 Ma - when the Altiplano-Puna Volcanic Complex entered in a steady-state stage. Such mafic products, mainly erupted near the border or outside of the well detected Altiplano-Puna Magma Body located in the upper crust, can help to unravel the evolution of the present-day Arc Magmatic Stage of this large volcanic silicic province. https://doi.org/10.1016/j.jsames.2019.102295

The great escape: Petrogenesis of low-silica volcanism of Pliocene to Quaternary age associated with the Altiplano-Puna Volcanic Complex of northern Chile (21°10′-22°50′S)

Osvaldo González-Maurelab, Petrus le Rouxb, Benigno Godoyc, Valentin R. Trollde, Frances M.Deegand, Andrew Menziesf a Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile b Department of Geological Sciences, University of Cape Town, Rondebosch 7700, South Africa c Centro de Excelencia en Geotermia de los Andes (CEGA) y Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile d Department of Earth Sciences, Natural Resources and Sustainable Development, Uppsala University, SE- 75236 Uppsala, Sweden e Instituto de Estudios Ambientales y Recursos Naturales (i-UNAT), Departamento de Física (Geología), Universidad de Las Palmas de Gran Canaria, Spain f Bruker Nano GmbH, Am Studio 2D, Berlin 12,489, Germany

Abstract

The Pliocene to Quaternary volcanic arc of the Central Andes formed on 70–74 km thick continental crust. Physical interaction between mafic and acid magmas for this arc are therefore difficult to recognize due to the differentiation of mantle-derived magma during ascent through the thickened crust and a corresponding lack of erupted primitive lavas. However, a rare concentration of less evolved rocks is located marginal to the partially molten Altiplano-Puna Magma Body (APMB) in the Altiplano-Puna Volcanic Complex of northern Chile, between 21°10′S and 22°50′S. To unravel the relationship between this less evolved magmatism and the APMB, we present major and trace element data, and Sr and Nd isotope ratios of fourteen volcanoes. Whole-rock compositional and Sr and Nd isotope data reveal a large degree for compositional heterogeneity, e.g., SiO2 = 53.2 to 63.2 wt%, MgO = 1.74 to 6.08 wt%, Cr = 2 to 382 ppm, Sr = 304 to 885 ppm, 87Sr/86Sr = 0.7055 to 0.7088, and 143Nd/144Nd = 0.5122 to 0.5125. The combined dataset points to magma spatial compositional changes resulting from magma mixing, fractional crystallization and crustal assimilation. The least evolved products erupted along the periphery of the APMB and are likely equivalent to the replenishing magmas that thermally sustain the large APMB system. We suggest that the mafic to intermediate eruptives we have investigated reflect mafic melt injections that underplate the APMB and escape along the side of the large felsic body to avoid significant compositional modifications during ascent, which helps to assess the evolution of the APMB through space and time. https://doi.org/10.1016/j.lithos.2019.105162

Magmatic differentiation at La Poruña scoria cone, Central Andes, northern Chile: Evidence for assimilation during turbulent ascent processes, and genetic links with mafic eruptions at adjacent San Pedro volcano

Osvaldo González-Maurelab, Benigno Godoyc, Petrus le Rouxb, Inés Rodríguezd, Carolina Maríne, Andrew Menziesa, Daniel Bertinf, Diego Moratac, Marina Vargasg a Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile b Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa c Centro de Excelencia en Geotermia de los Andes (CEGA), Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile d ANQA-Servicios Geológicos y Paleontológicos, Avelino Contardo 1041, Oficina 4, Antofagasta, Chile e Teck Resources Chile Limitada, Avenida Isidora Goyenechea 2800, Piso 8, Las Condes, Santiago, Chile f School of Environment, The University of Auckland, Private Bag 92019, Auckland, New Zealand g Maini, Unidad de Equipamiento Científico, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile 1 Present address: Departamento de Obras Civiles y Geología, Facultad de Ingeniería, Universidad Católica de Temuco, Rudecindo Ortega 02950, Temuco, Chile. 2 Present address: Bruker Nano GmbH, Am Studio 2D, Berlin 12,489, Germany.

Abstract

La Poruña (21°53′S; 68°30′W) is a 140 m high scoria cone composed of pyroclastic material and an extensive basaltic-andesite to andesite lava flow that is up to 8 km in length. Automated mineralogical analysis describes a suite of porphyritic mafic samples, comprising olivine- and pyroxene-bearing rocks. Well-defined major element compositional trends, as well as trace and rare earth element characteristics (e.g. Sr/Y < 47; Sm/Yb < 4), likely reflect magmatic differentiation at middle-upper crustal levels. Additionally, magma mixing and assimilation and fractional crystallization processes act on these La Poruña magmas within the thickened continental crust, which is typical in Andean volcanic systems. A remarkable compositional feature is the unusual reversed isotopic behaviour of increasing silica with decreasing 87Sr/86Sr compositions. In a process of crustal assimilation during turbulent magma ascent (ATA), the least differentiated rocks are the most contaminated ones since the turbulent hottest magmas effectively assimilate the crustal material. We relate the inverse Sr isotope trend to latter magmatic evolution involving ATA at shallow crustal levels prior to eruption, therefore differing from the broadly accepted Central Andean magmatic model. The older volcanics (>96 ka) from San Pedro volcano exhibit similar isotopic characteristics, therefore evidence of similar magmatic processes. This new dataset clearly defines magma compositional changes during the La Poruña eruption (ca. 100 ka), revealing an increase in crustal contamination at shallow crustal levels for the younger San Pedro lavas (<96 ka), likely controlled by increasing amounts of deep-sourced basaltic input over time. https://doi.org/10.1016/j.lithos.2019.03.033

The upper crustal magma plumbing system of the Pleistocene Apacheta- Aguilucho Volcanic Complex area (Altiplano-Puna, northern Chile) as inferred from the erupted lavas and their enclaves

Marco Taussia, Benigno Godoyb, Filippo Piscagliac, Diego Moratab, Samuele Agostinid, Petrus Le Rouxe, Osvaldo González-Maurelef, Guillermo Gallmeyerf, Andrew Menziesf, Alberto Renzulliac a Dipartimento di Scienze Pure e Applicate, Università degli Studi di Urbino Carlo Bo, 61029 Urbino, Italy b Centro de Excelencia en Geotermia de los Andes (CEGA), Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile c Spin Off Geo.In.Tech. srl, Campus Scientifico “Enrico Mattei”, Università degli Studi di Urbino Carlo Bo, 61029 Urbino, Italy d CNR - Istituto di Geoscienze e Georisorse, CNR, 56124 Pisa, Italy e Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa f Departamento de Ciencias Geológicas, Universidad Católica del Norte, Antofagasta, Chile

Abstract

The evolution of the magma plumbing system of the Pleistocene Apacheta-Aguilucho Volcanic Complex area (Altiplano-Puna Volcanic Complex, northern Chile) was investigated through petrographic, geochemical and isotopic studies of representative lavas and related enclaves. Updated available dates of these products, both from the Apacheta and Aguilucho stratovolcanoes and nearby domes, allow us to define the activity during the last 1 Ma. This investigation shows that the andesitic magmas were affected by processes of Assimilation plus Fractional Crystallization (AFC, with a significant role played by amphibole fractionation) during their ascent through the upper crust, presumably by the interaction with the Altiplano-Puna Magma Body (15–20 km). These andesitic magmas were erupted with no or minor additional contamination at shallower levels, or experienced plagioclase- dominated Fractional Crystallization (FC) to dacite within shallower crustal magma chambers (4–8 km depth). The constructional phase of the Apacheta and Aguilucho stratovolcanoes (≥1 to ca. 0.6 Ma) reflect a transition from high-flux (i.e. flare-ups) to steady state magmatism, as also documented in other Pleistocene volcanic complexes of the Altiplano-Puna Volcanic Complex. During this stage the mafic magma recharge was high enough to permit a large spectrum of hybridization of the resident magmas in the upper crust to form the abundant andesites and dacites lavas. In contrast, at ∼150–100 ka, the magmatism turned to a new stage of recharge (waning stage?) and the episodic intrusion of small-volumes of andesitic magmas permitted the remobilization of the crystal-rich dacites, triggering the extrusions of the Chanka, Chac-Inca and Cerro Pabellón domes. The andesitic enclaves in the domes studied here represent a snapshot of the magmatic processes of interaction that occurred in the shallower reservoir at the interface of the resident dacite with the ascending andesitic magma. Nevertheless, as there are no dated volcanic products from the area between 0.6 and 0.1 Ma, the youngest dacitic domes could also be interpreted as the beginning of a new magmatic pulse of the Altiplano-Puna Volcanic Complex. Independently from the significance of the mafic recharge at 150–100 ka (waning stage vs. new pulse) the youngest investigated domes share similar geochemical features and crustal depth constraints (4–8 km) with the ignimbrites of the Altiplano-Puna Volcanic Complex, therefore suggesting that the remobilized magmas erupted as the domes are possibly remains of older plumbing systems left over from the last magmatic flare-up of the Altiplano-Puna Volcanic Complex. https://doi.org/10.1016/j.jvolgeores.2019.01.021

Thermal, Deformation, and Degassing Remote Sensing Time Series (CE 2000– 2017) at the 47 most Active Volcanoes in Latin America: Implications for Volcanic Systems

K. Reath1 , M. Pritchard1 , M. Poland2 , F. Delgado1,3 , S. Carn4 , D. Coppola5 , B. Andrews6 , S. K. Ebmeier7 , E. Rumpf8, S. Henderson9 , S. Baker10 , P. Lundgren11 , R. Wright12, J. Biggs13 , T. Lopez14 , C. Wauthier15 , S. Moruzzi1, A. Alcott1, R. Wessels16, J. Griswold2, S. Ogburn2 , S. Loughlin17, F. Meyer14, G. Vaughan8, and M. Bagnardi7,11

1Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA 2U.S. Geological Survey – Cascades Volcano Observatory, Vancouver, WA, USA 3Équipe de Tectonique et Mécanique de la Lithosphère, Institut de Physique du Globe de Paris, Paris, France 4Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, MI, USA 5Department of Earth Sciences, Universita Delgi Studi di Torino, Torino, Italy 6Mineral Sciences, Smithsonian Institution, Washington, DC, USA 7School of Earth and Environment, University of Leeds, Leeds, UK 8U.S. Geological Survey –Astrogeology Science Center, Flagstaff, AZ, USA 9Earth and Space Sciences, University of Washington, Seattle, WA, USA 10University NAVSTAR Consortium (UNAVCO), Boulder, CO, USA 11Jet Propulsion Laboratory (JPL), California Institute of Technology, Pasadena, CA, USA 12Hawai’i Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI, USA 13School of Earth Sciences, University of Bristol, Clifton, UK 14Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA 15Department of Geosciences, Pennsylvania State University, University Park, PA, USA 16U.S. Geological Survey Headquarters, Reston, VA, USA, 17British Geological Survey, The Lyell Centre, Edinburgh, Scotland

Abstract Volcanoes are hazardous to local and global populations, but only a fraction are continuously monitored by ground-based sensors. For example, in Latin America, more than 60% of Holocene volcanoes are unmonitored, meaning long-term multiparameter data sets of volcanic activity are rare and sparse. We use satellite observations of degassing, thermal anomalies, and surface deformation spanning 17 years at 47 of the most active volcanoes in Latin America and compare these data sets to ground-based observations archived by the Global Volcanism Program. This first comparison of multisatellite time series on a regional scale provides information regarding volcanic behavior during, noneruptive, pre- eruptive, syneruptive, and posteruptive periods. For example, at Copahue volcano, deviations from background activity in all three types of satellite measurements were manifested months to years in advance of renewed eruptive activity in 2012. By quantifying the amount of degassing, thermal output, and deformation measured at each of these volcanoes, we test the classification of these volcanoes as open or closed volcanic systems. We find that ~28% of the volcanoes do not fall into either classification, and the rest show elements of both, demonstrating a dynamic range of behavior that can change over time. Finally, we recommend how volcano monitoring could be improved through better coordination of available satellite-based capabilities and new instruments. https://doi.org/10.1029/2018JB016199

Degassing-induced chemical heterogeneity at the 2011–2012 Cordón Caulle eruption

Rebecca Paisley*α, Kim Berloα, Jack Whattamβ, C. Ian Schipperβ, Hugh Tuffenγ

α Department of Earth Planetary Sciences, McGill University, 3450 Rue University, Montreal, Quebec, H3A 0E8, Canada β School of Geography, Environment and Earth Sciences, Victoria University, PO Box 600, Wellington 6140, New Zealand ϒ Lancaster Environment Centre, Lancaster University, LA1 4YQ, UK

Abstract The mechanisms of hazardous rhyolitic eruptions such as Cordón Caulle, Chile, in 2011– 2012 are controlled by poorly-understood shallow conduit processes. Here we characterise texturally and chemically heterogeneous domains (e.g. ash, breccias and tuffisites) generated via fracturing, gas fluxing and melt relaxation within the conduit, and preserved in glassy, oxidised and devitrified samples. Volatile trace element depletions (e.g. Zn, Pb) in relict degassing pathways record metal scavenging by fluxing gases. Diffusion modelling of preserved trace element concentration gradients (e.g. Li, Rb, Tl) at domain interfaces indicate deep-conduit degassing events were short-lived (~minutes) whereas late-stage venting from discrete locations was prolonged (~hours), corroborating visual observations of the eruption. Later-erupted vent deposits are volatile-depleted with respect to earlier- erupted bombs, indicating progressive syn-eruptive volatile loss. We show that a combination of in situ textural and volatile trace element analyses can provide new constraints on magmatic degassing in shallow systems depleted in H2O and CO2. https://doi.org/10.30909/vol.02.02.211237

Halogen (Cl, F) and sulphur release during explosive, effusive, and intrusive phases of the 2011 rhyolitic eruptionat Cordón Caulle volcano (Chile)

C. Ian Schipper*α, Jonathan M. Castroβ, Ben M. Kennedyγ, Bruce W. Christensonδ,Alessandro Aiuppaε, Brent Allowayζ,η, Pablo Forteβ, Gilles Seropianγ, Hugh Tuffenθ

α School of Geography, Environment and Earth Sciences, Victoria University, PO Box 600, Wellington 6140, New Zealand. β Institute of Geosciences, University of Mainz, Mainz, Germany. γ Geological Sciences, University of Canterbury, Christchurch, New Zealand. δ National Isotope Centre, GNS Science, PO Box 31-312, Lower Hutt 5040, New Zealand. ε Dipartimento DiSTeM, Università di Palermo. ζ School of Environment, The University of Auckland, Private Bag 92019, Auckland, New Zealand. η Instituto de Geografía, Pontificia Universidad Catolica de Chile, Av. Vicuna Mackenna, 4860, Santiago, Chile. θ Lancaster Environment Centre, Lancaster University, LA1 4YQ, UK.

Abstract We investigate sulphur, chlorine and fluorine release during explosive, effusive and intrusive phases the 2011-2012 Cordón Caulle eruption, with a focus on the halogens. Analysis of melt inclusions, pyroclasts and lava samples shows most sulphur to have degassed during magma decompression, but halogen release to have accompanied isobaric crystallisation in slowly-cooled magma that was emplaced in a lava flow and sub-vent intrusion. Fluorine in particular mobilised only after extensive groundmass crystallisation and incipient devitrification. By 2017, gas emitted from vent-proximal fumaroles had hydrothermal compositions, with HCl/HF ratios correlating with temperature. We estimate that the eruption could eventually emit up to 0.92 Mt of SO2, 6.3 Mt of HCl, and 1.9 Mt ofHF, but only∼16 wt.%,∼7 wt.% and∼2 wt.% of these were respectively emitted during opening explosive phases. Halogen devolatilisation and its associated hazards can persist long after rhyolite eruption and/or emplacement. https://doi.org/10.30909/vol.02.01.7390

Fabrics, facies, and flow through a large-volume ignimbrite: Pampa De Oxaya, Chile E. S. Platzman1, R. S. J. Sparks2, F. J. Cooper2

1 Department of Earth SciencesUniversity of Southern CaliforniaLos AngelesUSA 2 School of Earth SciencesUniversity of BristolBristolUK

Abstract

The Miocene Oxaya Formation, exposed along the western Andean slope in northern Chile, represents one of the largest ignimbrite provinces on earth. In this study, magnetic fabric data were acquired from a ~ 1-km-long core drilled vertically through a single cooling unit of the Oxaya Formation the ca.22 Ma Cardones ignimbrite. Samples for magnetic analysis were obtained every 20 m from the fine-grained matrix of the core. Detailed measurements of the variation in bulk magnetic properties, including natural remanent magnetization (NRM), susceptibility, and anisotropy of magnetic susceptibility (AMS), were used to monitor changes in magnetic mineralogy as well as changes in the strength and orientation of the magnetic fabric throughout the flow. AMS ellipsoid orientation and shape reflect rapid deposition from a concentrated granular fluidized flow and constrain both the location of the source caldera for this catastrophic eruption and processes of transport and deposition in this large-volume ignimbrite. After utilizing the magnetic remanence to correct for rotation about the core axis, well-grouped and imbricated petrofabric orientations reveal a well-defined SW (247°) transport direction down a proto-Western Andean slope indicating syn- or post-welding flow and confirming the deformed Lauca caldera as the likely source of the eruption. Systematic variations in fabric shape (T) and intensity (P) with depth reveal a predominately oblate fabric toward the top and base of the flow and predominately prolate fabrics in the center. These vertical changes in fabric reveal that this massive, apparently homogeneous, deposit has a systematic layering. This layering reflects depth-dependent temperature variations, temporal changes in the flow boundary zone during deposition and post-depositional processes. https://doi.org/10.1007/s00445-019-1345-2

Localised heating and intensive magmatic conditions prior to the 22–23 April 2015 Calbuco volcano eruption (Southern Chile)

Eduardo Morgado1,2, Daniel J. Morgan1, Jason Harvey1, Miguel-Ángel Parada2,3, Angelo Castruccio2,3, Raimundo Brahm2,3,4, Francisco Gutiérrez5, Bogomil Georgiev1, Samantha J. Hammond6

1 Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK 2 Centro de Excelencia en Geotermia de los Andes (CEGA-FONDAP 15090013), Santiago, Chile 3 Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile 4 Volcanic Risk Solutions, Institute of Agriculture and Environment, Massey University, Palmerston North 4442, New Zealand 5 GeoExpedition, Las Barrancas 25, Pirque, 9480000 Santiago, Chile 6 Environment, Earth and Ecosystems, The Open University, Milton Keynes MK7 6AA, UK

Abstract Calbuco volcano is a Late Pleistocene composite stratovolcano and member of the Southern Volcanic Zone of the Chilean Andes (41°19′S, 72°36′W). It lies ~ 20 km west of the Liquiñe– Ofqui Fault Zone, but is not located directly upon any major regional structures. During April 2015, a sub-Plinian eruption occurred, with a bulk erupted volume of ~ 0.3–0.6 km3 (~ 0.1– 0.2 km3 DRE). The eruption was a rapid-onset event that produced highly crystalline products (from 40 to 60 vol.%) including the mineral phases: plagioclase, clinopyroxene, orthopyroxene, amphibole, olivine, apatite, ilmenite, titanomagnetite and chalcopyrite. An upper-crustal reservoir is inferred using available geophysical data combined with amphibole geobarometry. Consideration of textural features, including high crystallinity, complex mineral zonation, crystal clots and interstitial glass between crystals from clots, suggests the presence of a mush zone within this reservoir. From the nine collected samples, whole-rock chemistry and an array of geothermometers (amphibole, amphibole- plagioclase, two-pyroxenes and Fe–Ti oxides) gave similar results for all samples possessing ~ 40 vol.% of crystals, with the exception of the sample Cal-160 (~ 60 vol.% crystallinity), which is slightly more evolved and yields lower temperatures for all geothermometers. By comparing temperatures calculated in sample Cal-160 using pairs of ilmenite- titanomagnetite core compositions with those calculated using rim compositions, we observe a late-stage temperature increase of between 70 and 200 °C. We suggest that this local-scale heating event was at least partly responsible for triggering the eruption. Our data suggest that the bulk of the erupted magma was derived from a relatively uniform (970– 1000 °C), crystal-rich magma mass. Sample Cal-160 was derived from a cooler environment (910–970 °C), where it was subjected to pre-eruptive heating to temperatures considerably higher than those observed in associated, erupted magmas (up to 1070 °C). This requires the involvement of a hot, presumably mafic magma injection at the base of a shallow, crystal-rich reservoir, though the mafic magma was not itself erupted. The localised nature of interaction and rapidity of eruption onset have implications for potential future hazards at Calbuco volcano. https://doi.org/10.1007/s00445-019-1280-2

Comparison of lake and land tephra records from the 2015 eruption of Calbuco volcano, Chile Keri McNamara1, Alison C. Rust1, Katharine V. Cashman1, Angelo Castruccio2,3, Ana M. Abarzúa4

1 School of Earth Sciences, University of Bristol, Bristol, UK 2 Departamento de Geología, Universidad de Chile, Santiago, Chile 3 Centro de Excelencia en Geotermia de los Andes, Santiago, Chile 4 Instituto de Ciencias de la Tierra y TAQUACH, Universidad Austral de Chile, Valdivia, Chile

Abstract Tephra layers in lake sediment cores are regularly used for tephrostratigraphy as isochronous features for dating and recording eruption frequencies. However, their value for determining volcanic eruption size and style may be complicated by processes occurring in the lake that modify the thickness and grain size distributions of the deposit. To assess the reliability of data from lake cores, we compare tephra deposited on land during the 2015 eruption of Calbuco volcano in Chile to records in sediment cores from three lakes of different sizes that are known to have received primary fall deposits. In general, the thickness and granulometry of the deposit in lake cores and nearby terrestrial sections are very similar. As anticipated, however, cores sampled close to (here, within 300 m of) fluvial inflows were affected by sediment deposition from the lake’s catchment; they differed from primary deposits not only in their greater thickness and organic content but also in poor sorting and lack of grading. Cores 850 m away from the inlet were not affected. We consider our results in the context of the particle settling regime as well as each lake’s location, bathymetry and catchment area. We find that the particle settling regime is important in more distal settings where the ash particles are small and particle settling occurs in density plumes rather than as individual particles. We conclude that lake cores can be useful for physical volcanology providing consideration is given to eruption parameters such as particle size and mass flux, as well as lake features such as bathymetry and catchment area. https://doi.org/10.1007/s00445-019-1270-4

Stratigraphically controlled sampling captures the onset of highly fluid- fluxed melting at San Jorge volcano, Southern Volcanic Zone, Chile

Lucy McGee1,2 , Eduardo Morgado1,3, Raimundo Brahm1,4, Miguel‑Ángel Parada1, Nicolas Vinet1, Luis E. Lara5,6, Andres Flores1, Michael Turner7, Heather Handley7, Geoff Nowell8

1 Centro de Excelencia en Geotermia de los Andes (CEGA), Department of Geology, Universidad de Chile, Santiago, Chile 2 Present Address: Department of Earth Sciences, School of Physical Sciences, University of Adelaide, Adelaide, Australia 3 Present Address: Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Leeds, UK 4 Present Address: Volcanic Risk Solutions, Institute of Agriculture and Environment, Massey University, Palmerston North, New Zealand 5 Servicio Nacional de Geología y Minería (SERNAGEOMIN), Santiago, Chile 6 Research Center for Integrated Risk Management (CIGIDEN), Santiago, Chile 7 Department of Earth and Planetary Sciences, Macquarie University, Sydney, Australia 8 Department of Earth Sciences, Durham University, Durham, UK

Abstract Volcanological studies coupled with detailed geochemistry can reveal important aspects regarding the melting and ascent processes of a magmatic body. The explosive part of the eruption giving rise to scoria and tephra deposits can hold a wealth of information which can complement chemical analyses of lava flows, however, it is often poorly exposed. A well-exposed scoria deposit and lava flow at the small eruptive center (SEC) San Jorge near Pucón in the Southern Volcanic Zone (SVZ), Chile, provides an opportunity to examine melting and storage processes in a primitive magma body almost in ‘real time’ through sampling up the stratigraphy of the deposit. This dataset comprises whole rock major and trace element chemistry, Sr–Nd and U-Th–Ra isotopes, in addition to mineral data through the eruption sequence. San Jorge whole rock compositions are unique in the area (MgO 10– 12 wt%, SiO2 50–52 wt%, Cr 600–900 ppm) and the studied tephras extend to the highest uranium- and radium-excesses yet measured in the SVZ. The unusual composition of the volcanic material displays similarities to rocks from the arc-front stratovolcano Villarrica but is distinct from other stratovolcanoes in the area, which exhibit greater influence from sediment input to the source, crustal assimilation and prolonged storage. We model the San Jorge magmas as a mixture of melts originating from highly fluid-fluxed, depleted mantle and fractionated basalt from the same source, with increasing amounts of the latter component with progression of eruption. This suggests that San Jorge-like magmas were the main feeder of the longer lived system building Villarrica. Abrupt major element variations up-sequence additionally show a rapid switch to more fractionated compositions, indicating that storage and evolution through crystallization may have taken place once the initially wet melts ‘dried out’. https://doi.org/10.1007/s00410-019-1643-x

Processes culminating in the 2015 phreatic explosion at Lascar volcano, Chile, monitored by multiparametric data.

Ayleen Gaete1 , Thomas R. Walter1 , Stefan Bredemeyer1,2, Martin Zimmer1 , Christian Kujawa1 , Luis Franco3 , Juan San Martin4 , Claudia Bucarey Parra3 1 GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany 2 GEOMAR Helmholtz Centre for Ocean Research Kiel, 24148 Kiel, Germany 3 Observatorio Volcanológico de Los Andes del Sur (OVDAS), Servicio Nacional de Geología y Minería (SERNAGEOMIN), Temuco, Chile. 4 Physics Science Department, Universidad de la Frontera, Casilla 54-D, Temuco, Chile. Correspondence to: Ayleen Gaete ([email protected])

Abstract

Small steam-driven volcanic explosions are common at volcanoes worldwide but are rarely documented or monitored; therefore, these events still put residents and tourists at risk every year. Steam-driven explosions also occur frequently (once every 2–5 years on average) at Lascar volcano, Chile, where they are often spontaneous and lack any identifiable precursor activity. Here, for the first time at Lascar, we describe the processes culminating in such a sudden volcanic explosion that occurred on October 30, 2015, which was thoroughly monitored by cameras, a seismic network, and gas (SO2 and CO2) and temperature sensors. Prior to the eruption, we retrospectively identified unrest manifesting as a gradual increase in the number of long-period (LP) seismic events in 2014, indicating an augmented level of activity at the volcano. Additionally, SO2 flux and thermal anomalies were detected before the eruption. Then, our weather station reported a precipitation event, followed by changes in the brightness of the permanent volcanic plume and (10 days later) by the sudden volcanic explosion. The multidisciplinary data exhibited short-term variations associated with the explosion, including (1) an abrupt eruption onset that was seismically identified in the 1–10 Hz frequency band, (2) the detection of a 1.7 km high white-grey eruption column in camera images, and (3) a pronounced spike in sulfur dioxide (SO2) emission rates reaching 55 kg sec−1 during the main pulse of the eruption as measured by a mini-DOAS scanner. Continuous CO2 gas and temperature measurements conducted at a fumarole on the southern rim of the Lascar crater revealed a pronounced change in the trend of the relationship between the carbon dioxide (CO2) mixing ratio and the gas outlet temperature; we believe that this change was associated with the prior precipitation event. An increased thermal anomaly inside the active crater observed through Sentinel-2 images and drone overflights performed after the steam-driven explosion revealed the presence of a fracture ~ 50 metres in diameter truncating the dome and located deep inside the active crater, which coincides well with the location of the thermal anomaly. Altogether, these observations lead us to infer that a lava dome was present and subjected to cooling and inhibited degassing. We conjecture that a precipitation event led to the short-term build-up of pressure inside the shallow dome that eventually triggered a vent-clearing phreatic explosion. This study shows the chronology of events culminating in a steam-driven explosion but also demonstrates that phreatic explosions are difficult to forecast, even if the volcano is thoroughly monitored; these findings also emphasize why ascending to the summits of Lascar and similar volcanoes is hazardous, particularly after considerable rainfall.

http://dx.doi.org/10.5194/nhess-2019-189

Seismic activity during the 2013–2015 intereruptive phase at Lascar volcano, Chile Ayleen Gaete1, Simone Cesca1, Luis Franco2, Juan San Martin3, Cristian Cartes3 and Thomas R. Walter1

1GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany. E-mail: [email protected] 2Observatorio Volcanologico de Los Andes del Sur (OVDAS), Servicio Nacional de Geología y Minería (SERNAGEOMIN), Temuco, Chile 3Physics Science Department, Universidad de la Frontera, Casilla 54-D, Temuco, Chile

Summary In addition to enabling the physical processes of volcanic systems to be better understood, seismology has been also used to infer the complexity of magma pathways and plumbing systems in steep-sided andesitic and stratovolcanoes. However, in these volcanic environments, the application of seismic location methods is particularly challenging and systematic comparisons of common methods are lacking. Furthermore, little is known about the characteristic seismicity and deep structure of Lascar volcano, one of the most historically active volcanoes in northern Chile known to produce VEI-4 eruptions. To better understand the inner processes and deep structure of Lascar, the local broad-band seismic monitoring network was densified during a temporal installation in 2014–2015. Herein, we focus on the local seismicity during the 2014–2015 unrest episode, during which we recorded numerous seismic events mainly classified as long-period (LP) type, but also denote volcano-tectonic (VT) activity. Specifically, a long-lasting phase of LP activity is observed over a period of ∼14 months that starts in tandem with a pulse of VT activity. The LP rate and amplitude are modulated over time; they are lower in the initial phase, rise during the intermediate period from October 2014 to July 2015, and finally slowly decay while approaching the eruption time. The location of LPs is challenging due to the typical lack of clear seismic onsets. We thus encompass this problem by comparing a broad range of different standard and novel location techniques to map the source region of LPs by fitting the amplitude decay, polarization patterns, coherence of characteristic functions and cross-correlation differential times. As a result, we principally constrain LP locations within the first 5 km depth below the summit extending downward along a narrow, conduit-like path. We identify different regions of complexity: VTs dominate at depth, both VTs and LPs cluster in an intermediate depth region (down to 1.5 km), suggesting a change in the plumbing system geometry, and LPs dominate the shallowest region. Based on these results, we infer the presence of a subvertical conduit extending down to a depth of ∼5 km, and a region of path divergence, possibly accommodating a magma plumbing system, at a depth of ∼3 km beneath the volcano summit. Identifying the locations of complexities in the magma pathways at Lascar may help identify future unrest. The results are compared with independent observations, demonstrating the strength of the location method used herein that will be tested at volcanoes elsewhere. https://doi.org/10.1093/gji/ggz297

Petrology, geochemistry, and correlation of tephra deposits from a large early-Holocene eruption of Mentolat volcano, southern Chile

D.J.Wellera, M.E.de Porrasb, A.Maldonadoc,d, C.Méndeze, C.R.Sterna a Department of Geological Sciences, University of Colorado, Boulder, CO, 80309-0399, USA b Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CONICET, CCT Mendoza, Av. Ruiz Leal s/n, Mendoza, Argentina c Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Instituto de Investigación Multidisciplinario en Ciencia y Tecnología, Universidad de La Serena, Avda. Raúl Bitrán, 1305, La Serena, Chile d Departamento de Biología Marina, Universidad Católica del Norte, Larrondo, 1281, Coquimbo, Chile e Centro de Investigación en Ecosistemas de la Patagonia (CIEP), Moraleda 16, Coyhaique, Chile

Abstract Two correlated tephra deposits, each 13 cm thick in the Aisén region of southern Chile, one in a lacustrine sediment core from the Mallín el Toqui (MET) peat bog and another from a subaerial soil exposure ∼10 km to the west in the Río Maniguales (RM) valley, preserve evidence for a large explosive eruption of Mentolat volcano, one of the five stratovolcanoes of the southernmost portion of the Andean Southern Volcanic Zone (SVZ). This eruption is constrained in age to ≥11,728 cal years BP by radiocarbon dating of organic matter from the MET sediment core and is termed the ∼11.7 ka MEN event. The two tephra deposits are identical and based on their petrology, bulk tephra, glass, and amphibole geochemical characteristics, are attributed to an eruption of Mentolat volcano. Both contain pumice lapilli with glass compositions that ranges from 59 to 76 wt. % SiO2, with medium to low- K2O calc-alkaline composition and trace element abundances similar to both lavas and other tephras derived from Mentolat. They have abundant amphibole, plagioclase, orthopyroxene, and clinopyroxene phenocrysts, with a smaller proportion of olivine and Fe- Ti oxides, and a minor amount of distinctive crustal xenoliths with both unfoliated and foliated textures. Amphiboles have low K2O (0.20–0.37 wt. %) and TiO2 (1.5–3.8 wt. %) and are similar geochemically to amphiboles from other Mentolat-derived tephra (K2O = 0.14– 0.43 wt. % and TiO2 = 1.9–2.4 wt. %), but distinct from amphiboles in lavas and tephra derived from other volcanoes in the southernmost SSVZ including Cay (K2O = 0.47–0.55 wt. % and TiO2 = 2.4–3.1 wt. %) and Melimoyu (K2O = 0.39–0.52 wt. % and TiO2 = 2.8–4.5 wt. %). Amphiboles from the ∼11.7 ka MEN tephra formed over a broad range of pressures (154–406 MPa), temperatures (834-969 °C), and magma water contents (4.9–7.0 wt. %), which overlap with the physical-chemical conditions for the formation of amphiboles from other Mentolat-derived tephra. The two correlated tephra deposits, which are located ∼95 km southeast of Mentolat, are correlative with tephra of similar age identified in 12 other lacustrine sediment cores from the region, for which, based on their petrology and the geochemistry of their tephra glass and amphiboles, Mentolat is also the likely source volcano. This eruption produced approximately 1.8 km3 of bulk material with an estimated magnitude of 5.2. Mentolat has produced numerous (>18) explosive eruptions since glacial retreat from the region and future explosive eruptions from this center could potentially impact local population centers and the agricultural industry in southern Chile and Argentina. https://doi.org/10.1016/j.jsames.2018.12.020

Analysis of the magmatic – Hydrothermal volcanic field of Tacora Volcano, northern Chile using travel time tomography

C.Pavezab, D.Comtebc, F.Gutiérrezd, D.Gaytáne a Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile. Plaza Ercilla 803, 13518, Santiago, Chile b Advanced Mining Technology Center, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile. Avenida Tupper 2007, 8370451, Santiago, Chile c Departamento de Geofísica, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile. Avenida Blanco Encalada 2002, 8370449, Santiago, Chile d GeoExpedition, Las Palomas 25, Pirque, Santiago, Chile e INFINERGEO SpA, Chile

Abstract Tacora Volcano (17°43′S – 69°46′W) lies at the southernmost end of a 10 km-long volcanic lineament that extends between Chile and Perú. Around Tacora volcano, thermal manifestations are two active fumarolic fields located at the western flank of the stratovolcano and at the volcano summit, indicating active magma degassing in a shallow hydrothermal system. Beneath Tacora volcano is located the NW Challaviento reverse fault that belongs to the Incapuquio - Challaviento fault system of Middle Eocene age. To complement previous exploration results and conceptual modeling developed by INFINERGEO SPA, seventeen short period seismic stations were installed around Tacora Volcano, between August and December 2014. Using the P and S wave arrival times of locally recorded seismicity, a 3D velocity model was determined through a travel time tomography. We interpreted high Vp/Vs values as water-saturated areas, corresponding to the recharge zone of Tacora hydrothermal system. In addition, low values of ΔVp/Vp (%) and Vp/Vs ratio represent the location of a gas-saturated magmatic reservoir and circulation networks of magmatic-hydrothermal fluids. Low Vp/Vs volumes (magma reservoirs/high temperature hydrothermal fluids), the presence of fumarolic fields and surface hydrothermal alteration have a spatial correlation. This suggests a structural control of the Challaviento fault in the hydrothermal flow. Finally, we present a cluster analysis using the ΔVp/Vp (%) parameter. Through this analysis, we found a method for the identification of a key structure in depth composed by the magma reservoir (low Vp/Vs ratios, low ΔVp/Vp (%)), clay level areas (intermediate values of ΔVp/Vp (%)), and degassification zones (low values of ΔVp/Vp (%)) directly related with the surface thermal manifestations. https://doi.org/10.1016/j.jsames.2019.102247

Administrando la Comunicación de Riesgos en una Emergencia Sanitaria, “El caso de la erupción del Volcán Calbuco”, Chile 2015 Leonardo Javier Díaz Bouquillarda aDepartamento de Comunicaciones, Secretaría Regional Ministerial de Salud, Chile Resumen

El siguiente trabajo presenta la estrategia comunicacional desarrollada por la institución Seremi de Salud, durante la emergencia sanitaria por la erupción del Volcán Calbuco (Región de Los Lagos, Chile) en abril del 2015, para disminuir los riesgos en la salud de las personas y comunidades expuestas a la erupción.

Se da cuenta de una estrategia preventiva e informativa a través de diversos materiales, incluyendo las redes sociales, además de la transparencia institucional en términos de información a la comunidad sobre calidad del aire, agua y ceniza. El análisis de las redes sociales institucionales (twitter) indica que los ejes discursivos sanitarios fueron adecuadamente apropiados y difundidos por la comunidad. https://doi.org/10.20318/recs.2019.4443

Preventing mental health risks in volunteers in disaster contexts: The case of the Villarrica Volcano eruption, Chile

Adriana E. Espinozaab, Paulina Osorio-Parraguezbc, Elvis Posada Quirogad

a Department of Psychology, University of Chile, Av. Ignacio Carrera Pinto 1045, 4th floor, Ñuñoa, Santiago, Chile b Nucleus of Research and Intervention in Emergencies and Disasters (NIID-UChile), University of Chile, Chile c Department of Anthropology, University of Chile, Av. Ignacio Carrera Pinto 1045, 2nd floor, Ñuñoa, Santiago, Chile d Consultant in Mental Health and Psychosocial Support in Humanitarian Institutions, QMSW 5 Lote 6 Bloco 6 Apto 399, Sudoeste, Brasilia DF, Brazil

Abstract Chile is a country that is constantly affected by natural disasters. In this article we present the results of a qualitative follow-up study with members of the Chilean Red Cross, who led the evacuation of the Pucón area after the Villarrica volcano eruption in 2015. The objectives were: to examine the experience of these volunteers throughout the evacuation; to describe their experience during a psychosocial intervention with art therapy called "Emotional Containment with Emergency Volunteers" to help them release their emotional exhaustion, and to determine the relevance of implementing psychosocial interventions with art therapy during the disaster response stage. First, we describe this art therapy intervention. Second, we present the study that included in-depth group interviews and a workshop called "Reflection on the intervention experiences after the eruption of the Villarrica volcano”, which uses art therapy techniques. The findings showed the importance of implementing psychosocial interventions with volunteers, both during the emergency and after the disaster. In this sense, the art therapy activities used allowed participants to identify and become aware of their physical and emotional levels of personal exhaustion. They also realized the importance of self-care and to take care of the other volunteers on the team. Another finding that is an emerging issue in the humanitarian organizations' work is the potential impact and stress level in volunteers during and after the response phases. Therefore, it is important to evaluate the responsibility of the organizations towards their volunteers for providing rest time, support and spaces for their emotional expression. https://doi.org/10.1016/j.ijdrr.2018.11.013

Geo-pedological contribution to the reconstruction of Holocene activity of Chaitén volcano (Patagonia, Chile)

Enrico Casatia, Michele D'Amicob, Ludek Šefrnac, Luca Trombinod, Annalisa Tunesia, Franco Previtalia a Department of Earth and Environmental Sciences, University of Milano - Bicocca, Italy b DISAFA, University of Torino, Italy c Department of Physical Geography and Geoecology, Charles University, Prague, Czech Republic d Department of Earth Sciences, University of Milano, Italy

Abstract

On May 2, 2008, the Chaitén volcano, located in Chilean Patagonia, thought to be inactive for almost 10,000 years, erupted, emitting pyroclastic materials (ash and pumice) of rhyolitic composition. The ejected materials partially burned the forest vegetation in a wide radius, blocked the river systems, causing local flooding, and forced the majority of the inhabitants to abandon the nearby village of Chaitén. In 2005, 2009, the authors surveyed and sampled a number of paleosols and tephra sections located just north of the village. The present work shows the results of pedological, micromorphological, petrographic, and geochemical analyses, accompanied by radiocarbon dating, The studies have shown the presence of different soil complexes (Andosols), developed from pyroclastic materials and separated by erosional surfaces. Under the modern soil, consisting only of A horizons, paleosols follow with pedogenized horizons overlying altered and hardened volcanic materials. The mineralogical and geochemical analyses confirmed the sequence of these complexes and distinguished a double origin of the materials from which they developed: the most recent and superficial soil, although not significantly affected by the depositions of the last eruption, presented an evident geochemical and mineralogical affinity with tephra of the Chaitén volcano, differently from those of the deeper paleosols which have been found to derive from the ejecta of Michinmahuida volcano. The evolutionary model of the soils of the area has also been confirmed by the dates measured along the studied sections that are comparable with the dates of volcanic events during the Holocene already ascertained by the most recent volcanological studies. https://doi.org/10.1016/j.jsames.2019.102222

Old magma and a new, intrusive trigger: using diffusion chronometry to understand the rapid-onset Calbuco eruption, April 2015 (Southern Chile)

Eduardo Morgado12, Daniel J. Morgan1, Angelo Castruccio2,3, Susanna K. Ebmeier1, Miguel-Ángel Parada2,3, Raimundo Brahm4, Jason Harvey1, Francisco Gutiérrez5, Richard Walshaw1

1 Institute of Geophysics and Tectonics, School of Earth and EnvironmentUniversity of LeedsLeedsUK 2 Centro de Excelencia en Geotermia de los Andes (CEGA-FONDAP 15090013)SantiagoChile 3 Departamento de Geología, Facultad de Ciencias Físicas y MatemáticasUniversidad de ChileSantiagoChile 4 Volcanic Risk Solutions, IAEMassey UniversityPalmerston NorthNew Zealand 5 GeoExpeditionSantiagoChile

Abstract In April 2015, an unpredicted rapid-onset eruption occurred at Calbuco Volcano, Southern Andes of Chile. This event consisted of two, sub-Plinian eruptions separated by a few hours. By analysis of Fe–Ti exchange between ilmenite and titanomagnetite crystals in samples of erupted material, we determine timescales of pre-eruptive heating experienced at the partially solidified chamber base and constrain the magma residence time for the bulk of the carrier magma. Analysis of the Fe–Ti oxide pairs from a sample retrieved from a pyroclastic density current deposit (Cal-160) shows that it was affected by a significant heating event (recording 70–220 °C of heating), while other collected samples did not record this late heating. This sample is interpreted to represent a piece of crystal mush located at the bottom of a prolate, ellipsoidal mush reservoir, mobilised < 4 days before the eruption by a triggering pulse of mafic magma considerably hotter than the typical magmatic temperature of the reservoir. Another two fall deposit samples (lapillus, Cal- 149Tb and Cal-155) of the eruption are interpreted to represent resident, eruptible magmas that did not interact with any magma recharge immediately prior to or during the eruption. We infer that these magmas had been at eruption temperature for some years based on their extensively equilibrated Fe–Ti oxides. https://doi.org/10.1007/s00410-019-1596-0

New age controls on the tephrochronology of the southernmost Andean Southern Volcanic Zone, Chile

DJ Weller (a1), ME de Porras (a2), A Maldonado (a3) (a4), C Méndez (a5) and CR Stern (a1)

(a1) Department of Geological Sciences, University of Colorado, Boulder, Colorado80309-0399, USA (a2) Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CONICET, CCT Mendoza, Av. Ruiz Leal s/n, Mendoza, Argentina (a3) Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Instituto de Investigación Multidisciplinario en Ciencia y Tecnología, Universidad de La Serena, Avda. Raúl Bitrán 1305, La Serena, Chile (a4) Departamento de Biología Marina, Universidad Católica del Norte, Larrondo 1281, Coquimbo, Chile (a5) Centro de Investigación en Ecosistemas de la Patagonia (CIEP), Moraleda 16, Coyhaique, Chile

Abstract The chronology of over 50 tephra layers preserved in a lake sediment core from Laguna La Trapananda (LLT) in the southern portion of the Andean Southern Volcanic Zone (SSVZ), Chile, is constrained by new radiocarbon age determinations, which span the period from late Pleistocene glacial retreat to the late Holocene. The tephra are correlative with tephra previously described from other lake cores in the region and are attributed to explosive eruptions of the SSVZ volcanoes Mentolat, Hudson, Macá, and potentially Cay. The new age determinations are used to estimate the ages of the >50 tephra in the LLT core, as well as those from the other previously described lake cores in the area, by a Bayesian statistical method. The results constrain the frequency of explosive eruptions of the volcanic centers in the southernmost SSVZ. They indicate that there was essentially no increase in the rate of eruptions from late-glacial to recent times due to deglaciation. They also provide isochrones used to constrain the depositional histories of the small lacustrine systems within which they were deposited and they provide a tephrochronologic tool for other paleoclimatic, paleoecologic, archaeologic and tephrochronologic studies in central Patagonia. https://doi.org/10.1017/qua.2018.81

Timber-framed building damage from tephra fall and lahar: 2015 Calbuco eruption, Chile

Josh L. Hayesa, Rodrigo Calderón B.b, Natalia I. Delignec, Susanna F. Jenkinsd, Graham S. Leonardc, Ame M. Mc Sporrana, George T. Williamsd, Thomas M.Wilsona a Department of Geological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand b National Geology and Mining Service, SERNAGEOMIN, Sta María 0104, Santiago, Chile c GNS Science, 1 Fairway Drive, Avalon, PO Box 30-368, Lower Hutt 6315, New Zealand d Earth Observatory of Singapore, Asian School of the Environment, Nanyang Technological University, Singapore 639798, Singapore

Abstract Assessing the damage to buildings from volcanic eruptions is an important aspect of volcanic risk assessment and management. However, there is a limited empirical evidence base to draw upon when describing the relation between volcanic hazard intensity and resulting physical damage. The 2015 subplinian eruption of Calbuco volcano, Chile, caused damage to buildings near the volcano because of tephra fall and lahars. Chilean authorities conducted a damage assessment of 961 properties (990 buildings) to inform an assistance programmer for property owners affected by the eruption. Property assessments typically contained observations and classification of damage to a house, and in some instances accessory buildings such as sheds, garages, and exterior storage rooms. In this study we used this unique damage data set to adapt damage state frameworks for tephra fall and lahar for classifying and analysing damage observations. We developed data quality indicators to provide transparency for how we accounted for data quality issues. We assigned a tephra and/or lahar damage state to 571 buildings (530 houses and 41 accessory buildings). The 419 buildings for which we did not assign a damage state either had too little information or fell outside of tephra and/or lahar hazard zones. The minimum tephra thickness isopach band that caused complete collapse was 10 to 15 cm (dry deposit loading ~1 to 1.6 kN m−2, saturated deposit loading 1.6 to 2.4 kN m−2), but most commonly (55% of tephra exposed DS5 houses n = 11), this occurred at 15 to 30 cm (dry deposit loading ~1.5 to 3.3 kN m−2, saturated deposit loading 2.4 to 4.8 kN m−2). Lahar damage was typically described as complete (DS5), with 26 houses being swept away or destroyed around the Blanco South River. Our results add to the limited evidence base of post-eruption tephra and lahar impacts to buildings and contribute to volcanic risk and impact assessment. https://doi.org/10.1016/j.jvolgeores.2019.02.017

Cryptic magma recharge associated with the most voluminous 20th century eruptions (1921, 1948 and 1971) at Villarrica Volcano

Christian Pizarroa,b, Miguel A.Paradaa,b, Claudio Contrerasa,b,c, Eduardo Morgadoa,b,d a Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, 803 Plaza Ercilla, 8370450 Santiago, Chile b Centro de Excelencia en Geotermia de los Andes (CEGA), Universidad de Chile, 803 Plaza Ercilla, 8370450 Santiago, Chile c School of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8, 1RJ, UK d Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK

Abstract Villarrica volcano is one of the most active volcanoes of the Andes (rest cycles of 5.4 ± 3.9 years) and erupts products of basaltic to basaltic-andesite compositions and in styles from Hawaiian to Vigorous Strombolian. We compare whole-rock geochemistry and mineral abundances, textures and compositions of the most voluminous basaltic lavas of the 20th century, which were erupted in 1921, 1948 and 1971. The analyzed lavas show a restricted range in whole-rock compositions (51.7–52.4 wt% SiO2), but there is an increasing trend of MgO content from 1921 (~5.3 wt% MgO) to 1948 (~7.0 wt% MgO) and a decreasing trend from 1948 to 1971 (~6.0 wt% MgO). Two groups of plagioclase compositions are observed in all lavas: An-poor (~An60) and An-rich (~An80). An-poor compositions are the most abundant in all lavas and were commonly formed in both the earliest (cores) and latest stages (external rims and small and nearly unzoned phenocrysts) of plagioclase crystallization, whereas An-rich plagioclase formed around An-poor cores during intermediate stages. Additionally, precipitation of An-poor plagioclase in both rims and cores could simultaneously have occurred in highly dissolved An-rich antecrysts. Equilibrium temperatures of plagioclase-olivine-clinopyroxene of about 1090 °C were obtained in crystal clots of the three lavas. Thermometry calculations obtained from MELTS simulations of plagioclase formation indicate a heating (thermal mixing) of the reservoir at ~0.5 kbar of up to 100 °C with respect to the crystal clots temperatures. Incorporation of small amounts of volatile-rich and hotter mafic magma of similar composition (cryptic mixing) into the Villarrica reservoir, could heat it, probably in a more efficient way than heat conduction alone. A longer interaction of the hot mafic magma within the reservoir could cause crystallization of An-rich plagioclase, dissolution of An-poor plagioclase (i.e. increase in An-rich/An-poor modal content ratios) and compositional modifications toward MgO- rich and volatile-rich compositions, that ultimately result in higher intensity of eruption. https://doi.org/10.1016/j.jvolgeores.2019.07.001

The unexpected explosive sub-Plinian eruption of Calbuco volcano (22–23 April 2015; southern Chile): Triggering mechanism implications

Fabio Arzillia, Daniele Morgavib, Maurizio Petrellib, Margherita Polaccia, Mike Burtona, Danilo Di Genovac, Laura Spinad, Giuseppe La Spinaa, Margaret E. Hartleya, Jorge E. Romeroe, Jonathan Fellowesa, Juan Diaz-Alvaradoe, Diego Peruginib a School of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UK b Department of Physics and Geology, University of Perugia, Piazza dell'Università, 06123 Perugia, Italy c Institute of Non-Metallic Materials, Clausthal University of Technology, Zehntner Str. 2a, 38678 Clausthal- Zellerfeld, Germany d Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Roma, Italy e Departamento de Geología, Universidad de Atacama, Av. Copayapu 485, Copiapó, Chile

Abstract Plinian-type eruptions are extremely hazardous, producing pyroclastic fallout and flows extending many kilometres from the vent. The most commonly invoked eruption trigger for Plinian-type eruptions is the intrusion of fresh magma, generally associated with precursory ground deformation and seismicity days/weeks before eruption. Closed-system internal triggering has also been proposed, such as protracted crystallisation of magma, which can produce a build-up of exsolved volatiles and thus pressurise the system prior to eruption. On 22–23 April 2015 Calbuco volcano, Chile, produced a sub-Plinian eruption with <3 h seismic precursory activity and no clear deformation signals in the preceding months. Here, we show that petrological and geochemical evidence do not support a hypothesis of eruption triggering due to pre-eruptive intrusion of fresh magma, but instead are consistent with an internal trigger. We found that basaltic andesitic magma was stored at depths between 8 and 12 km (i.e. 230–320 MPa) beneath Calbuco volcano before the 2015 eruption. The stored magma had an initial temperature of 900–950 °C, was water-saturated (5.5–6.5 wt% H2O) and formed phenocrysts of titanomagnetite, orthopyroxene, clinopyroxene and plagioclase cores (An78–93). Gradual cooling of the magma chamber produced thermal gradients and magma convection, evidenced by plagioclase overgrowth rims (An58–77) and blocky microlites (25–250 μm). Our interpretation is that this continuing crystallisation induced second boiling and an over-pressurisation of the system, leading to the rapid onset of the 2015 eruption. Petrological and geochemical evidence therefore shows that a closed-system magma chamber can evolve into a highly explosive eruption with very little precursory warning, posing a challenge for current volcano monitoring paradigms. We propose that internal triggering should be carefully considered as a mechanism for unexpected sub-Plinian eruptions, prompting a potential revision of existing hazard management strategies. https://doi.org/10.1016/j.jvolgeores.2019.04.006

Volcaniclastic sedimentation influenced by logjam breakups? An example from the Blanco River, Chile

Aldo M. Umazanoab, Ricardo N. Melchorab a INCITAP (Consejo Nacional de Investigaciones Científicas y Técnicas-Universidad Nacional de La Pampa), Mendoza 109, 6300, Santa Rosa, La Pampa, Argentina b Departamento de Geología, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa, Avenida Uruguay 151, 6300, Santa Rosa, La Pampa, Argentina

Abstract The Blanco River drains the southern flank of the Chilean Chaitén volcano toward the Pacific Ocean. During 2008, much of the rhyolitic tephra erupted by the volcano was remobilized by this (and others) fluvial system. In the Blanco River, the sediments were temporarily stored upstream of the valley dammed by logs, epiclastic and pyroclastic detritus. The logjam generation was controlled by a complex combination of several factors including abundant tephra influx, rains, steep topographic gradients, forest vegetation, and widening of the fluvial course. Sediment-laden flows generated by logjam breakup or overflow severely affected the downstream-located Chaitén village. The resulting sedimentary record is remarkable by the important proximal-distal changes in sediment composition, grain-size and types of flow within specific depositional episodes. Exposures of fluvial deposits underlying those of the 2008 eruption in the upland sector of the Blanco River display a similar sedimentary record suggesting a comparable hydro-sedimentary dynamics during deposition. This contribution analyzed the sedimentary succession that underlies the 2008 eruption deposits, in order to: i) document in detail the sedimentary processes occurred in the Blanco River as consequence of the interaction with the Chaitén volcano tephra and analyze if this hydro- sedimentary behavior departs from the expected response in similar situations; and ii) contribute to the dating of generation and rupture of logjams and exploration of the associated volcanic hazard. Basic methodology included facies analysis, recognition and correlation of depositional episodes, and 14C dating of wood and charcoal in the deposits. Four depositional episodes (named A to D) were identified within the proximal and distal fluvial segments. The proximal sector is located along the current fluvial course and the distal sector is a lowland floodplain area. In the proximal fluvial segment, the depositional episodes representing syn-eruptive conditions are composed by volcaniclastic gravels and sands, formed by stream flows (with different sediment concentration) and debris flows; and reworked ash and lapilli strata generated by the dilute flow-debris flow continuum. In this fluvial segment, particularly in the depositional episodes B and C, there are downstream facies and compositional changes that suggest recurrent generation and rupture of logjams. Depositional episode B probably occurred between 1216 and 1294 cal AD and 1391–1438 cal AD as suggested by the radiocarbon dates, and is related with the widespread “Vilcún Tephra” from the Chaitén volcano. In the distal fluvial segment the depositional episodes record sedimentation of volcaniclastic mud in ponded zones or temporally flooded areas, with incorporation of abundant organic matter, associated with sediment (sandy)-laden dilute flows and scarce preservation of ash-fall beds. It is further proposed that downstream compositional changes in syn-eruptive fluvial deposits (volcaniclastic sediments that change downstream to pyroclastic sediments) can be indicative of the presence of former logjams in similar fossil fluvial volcaniclastic sequences. https://doi.org/10.1016/j.jsames.2019.102477

Physicochemical models of effusive rhyolitic eruptions constrained with InSAR and DEM data: A case study of the 2011-2012 Cordón Caulle eruption

Francisco Delgadoa,b, Julia Kubanekc, Kyle Andersond, Paul Lundgrene, Matthew Pritcharda a Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA b Université de Paris, Institut de Physique du Globe de Paris, CNRS, F-75005 Paris, France c Department of Earth and Planetary Sciences, McGill University, Montreal, Canada d California Volcano Observatory, U.S. Geological Survey, Menlo Park, CA, USA e Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA Abstract The 9 month long 2011-2012 eruption of Cordón Caulle (Southern Andes, Chile) is the best instrumentally recorded rhyolitic eruption to date and the first time that the effusion of a rhyolitic flow has been observed in detail. We use Interferometric Synthetic Aperture Radar (InSAR), with time-lapse digital elevation models (DEMs) and numerical models to study the dynamics of coupled magma reservoir deflation and lava effusion. InSAR recorded 2.2-2.5 m of subsidence after the first three days of the eruption, which can be modeled using a spheroidal magma reservoir at a depth of ∼5 km, ∼20 km long, and with a pressure drop of 20-30 MPa. The source is elongated in the NW-SE direction and its large dimensions imply a large plumbing system active throughout the eruption and spanning neighboring volcanoes, with a slight change in the geometry halfway through the effusive phase. TanDEM-X and Pléiades DEMs record the extrusion of both the rhyolitic lava flow and the intrusion of a shallow laccolith around the eruptive vent after the third day of the eruption, with a total volume of ∼1.45 km3 DRE. The laccolith was emplaced during the first month of the eruption, during both the explosive and effusive stages of the eruption. Both the reservoir pressure drop and the extruded volume time series follow quasi-exponential trends, and can be explained by a model that couples the reservoir pressure decrease, time- and pressure-dependent variations in the magma properties inside of the reservoir, and conduit flow. This model predicts both the temporal evolution and amplitude of both time series during the effusive phase, and a magma compressibility of ∼10−10 Pa−1, half the reported compressibility of the magma of the sub-Plinian explosive phase. Further, we estimate that the reservoir contained 1-3 wt.% dissolved H2O at the onset of lava effusion, with no exsolved CO2 and H2O in the reservoir throughout the effusive phase. This implies that the magma was significantly degassed after the explosive phase. The remaining volatiles in the magma after the explosive stage might have caused magma fragmentation, consistent with the hybrid explosive-effusive style observed during the waning of the eruption. https://doi.org/10.1016/j.epsl.2019.115736

Early vegetation recovery after the 2008-2009 explosive eruption of the Chaitén Volcano

Ricardo Moreno-González1, Iván A. Díaz2, Duncan A. Christie3, Rafael E. Coopman4, Antonio Lara3

1 Department of Palynology and Climate Dynamic, University of Göttingen, Germany 2 Instituto de Conservación, Biodiversidad y Territorio, Universidad Austral de Chile, Valdivia, Chile 3 Instituto de Conservación, Biodiversidad y Territorio, Universidad Austral de Chile, Valdivia, ChileCenter for Climate and Resilience Research (CR)2 4 Instituto de Conservación, Biodiversidad y Territorio, Universidad Austral de Chile, Valdivia, ChileMarilyn Ball’s Lab, Plant Science Division, Research school of Biology, The Australian National University

Abstract In May 2008, Chaiten volcano entered in eruptive process, one of the world largest in the last time decades. The catastrophic event left different type of disturbance and caused diverse environmental damage. Consequently, the biological legacies were distributed heterogeneously in surrounding areas of the volcano. We went to the field to assess the early vegetation responses to the eruption a year after, September 2009. Particularly in the lateral-blast disturbance zone. We distributed a set of plots in three disturbed sites, and one in an undisturbed site. In each site, in a plot of 1000m2 we marked all stand tree, recording whether they were alive, resprouting or dead. Later in 80 small-plots (∼4m2) we tallied the plants regenerating, its coverage, and the log-volume. For regenerating plants, we described whether the substrate was mineral or organic. The impacts in the blast-zone created a gradient of disturbance, where close to the crater we found high devastation marked by the no surviving species, scarce standing-dead trees and logs, as well as no regeneration. On the other extreme, trees with devastated crown were resprouting, small- plants regrowing and dispersed seedlings. The main regeneration strategy was resprouting from trunks or buried roots, while few seedlings were observed in the small plots and elsewhere in disturbed areas. The main findings of this study are: i) a mosaic of pioneering- wind dispersed species, scattered survivors regrowing and spreading from biological legacies, and plant species dispersed by frugivorous birds, likely favored by the biological legacies; (ii) the early succession is influenced by the interaction of the species-specific life history, altitudinal gradient and the different intensity of disturbance. https://doi.org/10.1101/746859

Statistical separation of tectonic and inflation-driven components of deformation on silicic reservoirs, Laguna del Maule volcanic field, Chile

N. Garibaldia, B. Tikoffa, D. Petersonb, J.R. Davisc, K. Keranenb a Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA b Cornell University, Ithaca, NY, USA c Carleton College, Northfield, MN, USA

Abstract The reconstruction of the structural history of inflating silicic systems is challenging because their faulting record encompasses tectonic and inflation-driven deformation, and separating the two can rarely be accomplished. Here, we present and utilize a statistical methodology to differentiate tectonic from inflation-driven deformation in the Laguna del Maule (LdM), a post-glacial rhyolitic volcanic field (Southern Volcanic Zone, Chile, latitude 36° S). LdM is cut by the Troncoso fault, a major normal fault that strikes NE and dips to the NW. The Troncoso hanging wall contains abundant, young (< 23 ka) NE-striking normal faults, whereas the footwall is largely unfaulted, with few NNW-striking faults. Activity within the shallow (<8 km) LdM reservoir has caused two inflation events, both centered in different areas of the footwall: 1) a geodetic-based (InSAR) inflation, acting since 2007; and 2) a shoreline-based inflation, evidenced by warping of a 9.4 ka high-stand shoreline. To separate tectonic and inflation-driven faults in the Troncoso hanging wall, we perform a statistical analysis of fault orientation to compare them to the elongation direction predicted by tectonics. The orientation of normal faults is consistent with NW-SE tectonic elongation recorded outside the inflating area. To evaluate if either inflation event has reactivated these tectonic faults, we perform a statistical analysis of orientation-and-heave (horizontal offset on a fault): we calculate the maximum elongation direction (the accumulated horizontal offset) and compare it to elongation predicted by tectonics, shoreline-based inflation and geodetic-based inflation. The maximum elongation direction is sub-parallel to elongation predicted by shoreline-based inflation and is statistically different from tectonic elongation. We interpret a first stage of tectonic extension (>19–9.4 ka) where normal faults are developed on the Troncoso hanging wall. During shoreline- based inflation (<9.4 ka), faults on the hanging wall are reactivated, suppressing uplift; the largely unfaulted footwall uplifts instead. The differential uplift is accommodated by slip on the Troncoso fault. The current, geodetic based uplift, nucleates few faults with large offsets, and potentially reactivates the Troncoso fault. From the structural history, we suggest that the structural architecture is associated with surface volcanism: deformation of the Troncoso hanging wall appears to facilitate repeated, small volume, post-glacial rhyodacitic and andesitic eruptions, whereas the largely unfaulted Troncoso footwall seems to favor rhyolite accumulation and eruption during the late Holocene. https://doi.org/10.1016/j.jvolgeores.2019.106744

Conductivity Distribution Beneath the San Pedro‐Linzor Volcanic Chain, North Chile, Using 3‐D Magnetotelluric Modeling

Renzo Mancini 1,2, Daniel Díaz1,2, Heinrich Brasse3, Benigno Godoy2, María José Hernández1

1 Departamento de Geofísica, Universidad de Chile, Santiago, Chile 2 Centro de Excelencia en Geotermia de Los Andes, Santiago, Chile 3 Fachrichtung Geophysik, Freie Universität Berlin, Berlin, Germany

Abstract A magnetotelluric study was carried out in the San Pedro‐Linzor volcanic chain, North Chile, to identify possible magmatic structures and hydrothermal systems associated with volcanoes of Holocene activity, considering previous petrochemical studies pointing to crystallization depths of approximately 8 km. Three‐dimensional resistivity models based on magnetotellurics data of the San Pedro‐Linzor volcanic chain were obtained based on broadband data measured in 2017 and 2018, in addition to long‐period data measured in 1990s. The three‐dimensional modeling shows two low‐resistivity zones (less than 10 Ωm) interpreted as partially molten areas below the Chao Dome and the Paniri volcano, and a shallower low resistivity area (less than 5 Ωm) in the Turi Basin, an active hydrothermal system to the southwest of the volcanic chain. https://doi.org/10.1029/2018JB016114

Dynamics of Outgassing and Plume Transport Revealed by Proximal Unmanned Aerial System (UAS) Measurements at Volcán Villarrica, Chile

Emma J. Liu1, Kieran Wood2, Emily Mason1, Marie Edmonds1, Alessandro Aiuppa3, Gaetano Giudice4, Marcello Bitetto3, Vincenzo Francofonte4, Steve Burrow2, Thomas Richardson2, Matthew Watson5, Tom D. Pering6, Thomas C. Wilkes6, Andrew J. S. McGonigle3, Gabriela Velasquez7, Carlos Melgarejo7, Claudia Bucarey7

1 Department of Earth Sciences, University of Cambridge, Cambridge, UK 2 Department of Aerospace Engineering, University of Bristol, Bristol, UK 3 Dipartimento DiSTeM, Università di Palermo, Palermo, Italy 4 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Palermo, Italy 5 School of Earth Sciences, University of Bristol, Wills Memorial Building, UK 6 Department of Geography, University of Sheffield, Winter Street, UK 7 Observatorio Volcanológico de los Andes del Sur (OVDAS), Red Nacional de Vigilancia Volcánica (RNVV), Servicio Nacional de Geología y Minería, Temuco, Chile

Abstract Volcanic gas emissions are intimately linked to the dynamics of magma ascent and outgassing and, on geological time scales, constitute an important source of volatiles to the Earth's atmosphere. Measurements of gas composition and flux are therefore critical to both volcano monitoring and to determining the contribution of volcanoes to global geochemical cycles. However, significant gaps remain in our global inventories of volcanic emissions, (particularly for CO2, which requires proximal sampling of a concentrated plume) for those volcanoes where the near‐vent region is hazardous or inaccessible. Unmanned Aerial Systems (UAS) provide a robust and effective solution to proximal sampling of dense volcanic plumes in extreme volcanic environments. Here we present gas compositional data acquired using a gas sensor payload aboard a UAS flown at Volcán Villarrica, Chile. We compare UAS‐derived gas time series to simultaneous crater rim multi‐GAS data and UV camera imagery to investigate early plume evolution. SO2 concentrations measured in the young proximal plume exhibit periodic variations that are well correlated with the concentrations of other species. By combining molar gas ratios (CO2/SO2 = 1.48–1.68, H2O/SO2 = 67–75, and H2O/CO2 = 45–51) with the SO2 flux (142 ± 17 t/day) from UV camera images, we derive CO2 and H2O fluxes of ~150 t/day and ~2,850 t/day, respectively. We observe good agreement between time‐averaged molar gas ratios obtained from simultaneous UAS‐ and ground‐based multi‐GAS acquisitions. However, the UAS measurements made in the young, less diluted plume reveal additional short‐term periodic structure that reflects active degassing through discrete, audible gas exhalations. https://doi.org/10.1029/2018GC007692

Intra‐Arc Crustal Seismicity: Seismotectonic Implications for the Southern Andes Volcanic Zone, Chile

Gerd Sielfeld1,2 , Dietrich Lange3 , and José Cembrano1,2

1 Pontificia Universidad Católica de Chile, Chile, 2 Centro de Excelencia en Geotermia de Los Andes, CEGA, Chile, 3 GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany

Abstract We examine the intra‐arc crustal seismicity of the Andean Southern Volcanic Zone. Our aim is to resolve interseismic deformation in an active magmatic arc dominated by both margin‐parallel (Liquiñe‐Ofqui fault system, LOFS) and Andean transverse faults. Crustal seismicity provides information about the schizosphere tectonic state, delineating the geometry and kinematics of high strain domains driven by oblique‐subduction. Here, we present local seismicity based on 16‐month data collected from 34 seismometers monitoring a ~200‐km‐long section of the Southern Volcanic Zone, including the Lonquimay and Villarrica volcanoes. We located 356 crustal events with magnitudes between Mw 0.6 and Mw 3.6. Local seismicity occurs at depths down to 40 km in the forearc and consistently shallower than 12 km beneath the volcanic chain, suggesting a convex shape of the crustal seismogenic layer bottom. Focal mechanisms indicate strike‐slip faulting consistent with ENE‐WSW shortening in line with the long‐term deformation history revealed by structural geology studies. However, we find regional to local‐scale variations in the shortening axes orientation as revealed by the nature and spatial distribution of microseismicity, within three distinctive latitudinal domains. In the northernmost domain, seismicity is consistent with splay faulting at the northern termination of the LOFS; in the central domain, seismicity distributes along ENE‐ andWNW‐striking discrete faults, spatially associated with, hitherto seismic Andean transverse faults. The southernmost domain, in turn, is characterized by activity focused along a N15°E striking master branch of the LOFS. These observations indicate a complex strain compartmentalization pattern within the intra‐arc crust, where variable strike‐slip faulting dominates over dip‐slip movements.

10.1029/2018TC004985

Oblique-slip tectonics in an active volcanic chain: A case study from the Southern Andes

Javiera Ruzab, Andrea Brogide, José Cembranoabc, Ashley Stanton-Yongecf, PamelaPérez-Florescg, PabloIturrietaac a Departamento de Ingeniería Estructural y Geotécnica, Pontificia Universidad Católica de Chile, Vicuña Mackena 4860, Santiago, Chile b Centro de Excelencia en Geotermia de los Andes (CEGA, Fondap-Conicyt 15090013), Chile c Cirrus SpA - Geoscience d Dipartimento di Scienze della Terra e Geoambientali, Università di Bari, Via Orabona 4, Bari. Italy e CNR-IGG, Via Moruzzi 1, Pisa. Italy f Rock & Ice Physics Laboratory and UCL Seismolab, University College London g CIGEA Ltda

Abstract

Oblique-slip tectonics in the intra-arc region of the Southern Andes accommodates heterogeneous deformation derived from plate convergence during the Pliocene and Quaternary. Long-term mechanical interaction between Andean transverse faults (i.e. NW- striking sinistral faults) and margin-parallel faults (i.e. NNE-striking faults) results in linked transtensional fault damage zones that facilitate structural conditions for the migration and emplacement of geofluids in the upper crust. We investigated the architecture of pre- eruptive units and the nature of faulting at the Tatara–San-Pedro–Pellado volcanic complex in the Southern Andes. Here, oblique-slip faulting crosscuts Miocene folded strata and granitoids. Our main results suggest that Quaternary volcanism and an associated geothermal systems developed on top of an ENE-oriented structural anisotropy defined by hundreds of faults and dikes interacting in a ca. 9 km long and 4 km wide rock volume, named the Tatara Damage Zone. Deformation in this domain is characterized by ENE- to WNW-striking transtensional oblique-slip faults flanked by (1) the seismically active NS- striking (dextral) Melado Fault to the west, (2) discrete NS- to ENE-striking dextral splay faults to the east and (3) the sinistral NW-striking Los Cóndores Fault to the north-east, which is reported for the first time in this work. The latter fault represents an excellent example of a long-lived Andean Transverse Fault. Furthermore, we suggest that the Los Cóndores Fault accommodates a margin-oblique slip component of bulk transpressional deformation. We demonstrate that Pliocene–Quaternary intra-arc oblique faulting developed after pre-Late Miocene compressional tectonics, and that this oblique faulting constrains the geometry of permeable pathways for the flow, emplacement, and eruption of quaternary geofluids. Furthermore, we evaluated the stress field for a discrete volcanic complex and provided key elements to better understand the role of Andean Transverse Faults in the spatial organization of Quaternary arc volcanism and geothermal systems in the Southern Andes. https://doi.org/10.1016/j.tecto.2019.228221

Magma Reservoir Below Laguna del Maule Volcanic Field, Chile, Imaged With Surface‐Wave Tomography

Crystal E. Wespestad1, Clifford H. Thurber1, Nathan L. Andersen2, Brad S. Singer1, Carlos Cardona3, Xiangfang Zeng4, Ninfa L. Bennington1, Katie Keranen5, Dana E. Peterson5 , Darcy Cordell6, Martyn Unsworth6, Craig Miller7 , and Glyn Williams‐Jones8

1Department of Geoscience, University of Wisconsin‐Madison, Madison, WI, USA, 2Department of Earth Science, University of Oregon, Eugene, OR, USA, 3Observatorio Volcanológico de los Andes del Sur, Servicio Nacional de Geología y Minería, Temuco, Chile, 4State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics Chinese Academy of Sciences, Wuhan, China, 5Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA, 6Department of Physics, University of Alberta, Edmonton, Alberta, Canada, 7GNS Science, Taupo, New Zealand, 8Centre for Natural Hazards Research, Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia, Canada

Abstract. The Laguna del Maule (LdM) volcanic field comprises the greatest concentration of postglacial rhyolite in the Andes and includes the products of ~40 km3 of explosive and effusive eruptions. Recent observations at LdM by interferometric synthetic aperture radar and global navigation satellite system geodesy have revealed inflation at rates exceeding 20 cm/year since 2007, capturing an ongoing period of growth of a potentially large upper crustal magma reservoir. Moreover, magnetotelluric and gravity studies indicate the presence of fluids and/or partial melt in the upper crust near the center of inflation. Petrologic observations imply repeated, rapid extraction of rhyolitic melt from crystal mush stored at depths of 4–6 kmduring at least the past 26 ka. We utilize multiple types of surface‐wave observations to constrain the location and geometry of low‐velocity domains beneath LdM. We present a three‐dimensional shear‐wave velocity model that delineates a ~450‐km3 shallow magma reservoir ~2 to 8 km below surface with an average melt fraction of ~5%. Interpretation of the seismic tomography in light of existing gravity, magnetotelluric, and geodetic observations supports this model and reveals variations in melt content and a deeper magma system feeding the shallow reservoir in greater detail than any of the geophysical methods alone. Geophysical imaging of the LdM magma system today is consistent with the petrologic inferences of the reservoir structure and growth during the past 20–60 kyr. Taken together with the ongoing unrest, a future rhyolite eruption of at least the scale of those common during the Holocene is a reasonable possibility. https://doi.org/10.1029/2018JB016485

Silicic volcanism triggered by increased denudation rates in the Quaternary Andean arc of central Chile between 33°50'-34°30'S

Marcia Muñoz-Gómezab Ítalo Payacáncde, Francisco Gutiérreze, Marcelo Faríasd, Reynaldo Charrierad, Mireille Polvéf a Escuela de Ciencias de La Tierra, Facultad de Ingeniería, Universidad Andres Bello, Campus República, Salvador Sanfuentes, 2357, Santiago, Chile b Advanced Mining Technology Center (AMTC), Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Av. Tupper, 2007, Santiago, Chile c Escuela de Geología, Universidad Mayor, Manuel Montt 367, Providencia, Santiago, Chile d Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Casilla, 13518, Correo 21, Santiago, Chile e GeoExpedition, Las Palomas 25, Pirque, Santiago, Chile f GET, Université de Toulouse, CNRS, IRD, OMP, Av. Edouard Belin, 31400, Toulouse, France

Abstract

In central Chile (33°50′-34°30′S), the Quaternary arc records a distinctive episode of silicic volcanism (SiO2 >70 wt%) that occurred during latest Pleistocene (0.1–1 Ma). This episode is recorded in several eroded and inactive arc centers distributed mostly along the highest summits of the Andes in the same region covered by the modern arc centers. We report new data including field observations, petrography, whole rock chemical and Sr-Nd isotopic analyses, mineral chemistry and geochronology for the Quaternary Andean arc in the region with emphasis in the latest Pleistocene units (0.1–1 Ma). The silicic episode that the latter units represent constitutes a singularity in the common compositions that characterize in the long term this arc segment, as it is preceded and followed by basaltic andesite-andesite- dacite suite compositions. In addition, it occurs coevally with a period of increased denudation resulting from the major uplift event of the Andean orogen in the area. Geologic field markers, supported by thermobarometric estimations, indicate conservative estimates of denudation of ∼1.5 km during this period in the area which in turn accounts for a significant pressure decrease at upper crustal levels that must have affected the shallow reservoirs that fed the arc volcanoes. For evaluating this, thermodynamic numerical simulations have been run at different pressure conditions in order to describe for such magmatic systems the evolution in terms of major element composition, degree of crystallinity and volatile content with the temperature decrease. Overall, results show that the compositional spectra defined by this arc segment can be reproduced by low pressure (<0.75 kbar) crystallization of its most basic members by batch and/or fractional processes, the latter being indispensable to reproduce the most evolved compositions. Results also show that a sudden pressure decrease creates a unique set of conditions that constructively operate for prompting the rapid generation and extraction of silicic melts, among the main factors it is highlighted the sudden devolatilization and enhanced crystal-melt segregation which is expected to lead to the rapid creation of a volatile saturated silicic cap in the magma reservoirs. This in turn can account for a compositional change of the volcanoes that tap them, as is seen in the evolution of the Quaternary Andean arc in the study area. The transitory nature of such silicic volcanic episode, characterized by a return to the basaltic andesite-andesite-dacite suite compositions, follows from the transience of the increased denudation event and marks the reaching of a new steady state for the tectono- magmatic system. https://doi.org/10.1016/j.lithos.2019.105242