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Cerro Overo maar and La Albóndiga lava dome are two independent monogenetic volcanoes located in the Central Volcanic Zone of the Andes in northern Chile, close to the active Lascar and Chiliques volcanoes. Cerro Overo maar was formed <77 ka ago by explosive-effusive eruptions, including phreatomagmatic activity, while La Albóndiga lava dome (Pleistocene) is the result of magmatic explosive-effusive activity alone. Cerro Overo and La Albóndiga are characterized by deposits composed of pyroclastic rocks and dense coherent lava blocks. At Cerro Overo, these deposits are located around the crater rim, while at La Albóndiga, they form coherent in situ lava dome features. Cerro Overo also displays thin ash- and lapilli-dominated deposit layers presumed to be pyroclastic surge deposits, which include juvenile pyroclasts exhibiting cauliflower textures, numerous exotic accidental lithics, and ballistically transported lapilli, bombs, blocks, and bomb sags. These fragments include recycled, juvenile pyroclasts, as well as material from older volcanic and intrusive rocks from the stratigraphic units immediately below. These small-volume volcanoes represent two of the less silicic volcanoes (~54 wt.% SiO2) in the northern Chilean Pleistocene to Holocene volcanic provinces. They are characterized by a fine grain size (mainly fine lapilli), olivine phenocrysts with skeletal textures, ignimbritic, dioritic, and granitic xenoliths, and quartz xenocrysts, with high concentrations of incompatible trace elements and light rare earth elements. The general magmatic evolution of the Cerro Overo and La Albóndiga systems has been controlled by fast ascent (e.g., skeletal olivine phenocrysts) of mantle-derived magma associated with mixing, fractional crystallization, and a low degree of crustal assimilation during turbulent ascent processes. Such eruptions provide evidence that various factors play an essential role in the transition from explosive-effusive magmatic (Cerro Overo and La Albóndiga) to phreatomagmatic (Cerro Overo) volcanic eruption styles. [ABSTRACT FROM AUTHOR]

The Negros de Aras monogenetic volcanic field in the Central Volcanic Zone of the Andes displays the highest concentration of scoria cones in northern Chile (0.23 per km2). It contains 66 vents, 22 of which are emission points of lava flows without an associated recognizable volcanic edifice, whereas 44 are typical scoria cones. Most vents are associated with basaltic andesite and andesite lava flows of up to 4.6 km in length. A few scoria cones show signs of either initial or final phreatomagmatic eruptions recorded in their pyroclastic successions. A geomorphological, morphometric, and spatial distribution analysis of the scoria cones of this volcanic field was carried out with the purpose of identifying the factors and processes that governed their emplacement, growth, and final morphology. The morphometric analysis was performed on 16 well-delimited scoria cones applying the MORVOLC algorithm using the TanDEM-X 12 m resolution digital elevation model. Analysis of the distribution and elongation of the craters of the scoria cones defines four alignments inferred to be related to the local and regional structural elements of the area. Volcanic activity seems to have been related to a N-S fault system with an E-W maximum stress orientation, favoring magma ascent and scoria cone emplacement following inherited fractures in these preferential orientations. The scoria cones show a wide range of morphologies and morphometries that can be related to different syn - and post-eruptive processes. Cones with large craters and high crater width / basal width ratios show clear evidence of phreatomagmatic eruptions (within their pyroclastic successions), whereas horseshoe-type cones are related to cone breaching or coeval lava flow effusion, and more pristine (i.e., relatively younger) cones are generally steeper. • First morphometric analysis of scoria cones in northern Chile. • Negros de Aras volcanic field contains 66 volcanic centers (44 scoria cones and 22 vents). • A local extensive regime and inherited N-S structures determined the spatial distribution of the scoria cones. • The MORVOLC algorithm with a TanDEM-X 12 m spatial resolution was used for calculating morphometric parameters. [ABSTRACT FROM AUTHOR]

Effusion rate is the instantaneous lava flow output by a vent. It is one of the most important factors that govern the emplacement and dynamics of lava flows and can be determined by direct measurements or estimated through modeling. The Negros de Aras monogenetic volcanic field, located in the Central Volcanic Zone of the Andes, is the largest volcanic field in northern Chile. It is situated north of the active Socompa volcano and south of the Salar de Atacama basin, consisting of scoria cones and lava flows. Here, we estimate the effusion rates of three overlapping and representative solidified lava flows from this volcanic field applying an iterative procedure using the Q-LavHA GIS plugin, where the effusion rate is treated as an unknown parameter and the solution is reached by comparing the simulated results with the real extension of the flows. The pre-eruptive surface was reconstructed using the 12 m resolution TanDEM-X digital elevation model. Other required input parameters for the modeling (e.g., channel ratio, viscosity, temperature) were estimated through geomorphometric, petrographic, and geochemical analysis. The estimated effusion rates vary between 14 and 113 m3/s, comparable with rates measured elsewhere. The method was validated by applying it to two directly measured (Nyamuragira 2006; Mount Etna 2001) and one calculated effusion rate (Lentiscal 2450 BP, Canary Islands). The estimated effusion rates gave an average underestimation of 10%. Considering this percentage of adjustment, the effusion rates for the three studied lava flows from the Negros de Aras monogenetic volcanic field vary from 15 m3/s to 124 m3/s. Our results provide valuable information for mitigating volcanic risk in the event of future lava flow eruptions, which could affect nearby villages and mining operations. • Estimation of effusion rate of cooled lava flows in the Negros de Aras monogenetic volcanic field. • Estimation of effusion rate using the lava flow simulation software Q-LavHA GIS. • Lava flows morphotypes vary from 'a'ā type to blocky type. • The pre-eruptive surface was modeled using the TanDEM-X 12 m spatial resolution digital elevation model. [ABSTRACT FROM AUTHOR]

The Tilocálar volcanic complex comprises four monogenetic volcanoes located at the southeastern edge of the Salar de Atacama Basin, northern Chile. These monogenetic volcanic centers are the Tilocálar Norte lava, the El Maní dome, the Tilocálar Sur small–lava shield, and the Tilocálar Sur maar, respectively, and were formed between 460 ± 50 ka to < 1 Ma ago along the north–south-striking Tilomonte ridge that underlies the Tucúcaro Ignimbrite (3.2 ± 0.3 Ma). Their formation is the result of an intermediate magma rising to the surface during a local transtensional regime, which is observed at El Maní, under a dominantly compressional tectonic setting. The Tilocálar monogenetic centers provide a rare opportunity to examine the variability from individual and small–volume magma batches to the development of a monogenetic volcanic field. These volcanoes and the control on their eruption styles were studied by geological mapping and stratigraphic considerations, morphometric analysis, textural studies (density and vesicularity), petrographic observations, and geochemical analyzes. The Tilocálar Norte lavas have an intermediate composition (mostly andesite, 62.02 wt.% SiO 2) that reach a maximum distance of 3.9 km to the north and 1.2 km to the southwest from their vent, with a dense–rock equivalent (DRE) volume of 8.73×107 m3. The El Maní lava dome is small (covering 750 m2 area and consisting of 1.06×103 m3 DRE volume) that presents mingled mafic (63.89 wt.% SiO 2) and felsic (73.73 wt.% SiO 2) products of the original magma source, related to shallow crustal melts. The Tilocálar Sur small lava–shield is characterized by a pyroclastic fall deposit and lavas. The pyroclastic fall deposit is characterized by agglutinated andesite scoria–spatter fall units, covering 2.81 km2 and consisting of 7.75×105 m3 DRE volume. In contrast, the lavas are characterized by an andesitic composition (57.64 wt.% SiO 2), which is 1.8 km in length to the northwest and 1.4 km to the east of their source. These lavas cover an area of 3.78 km2 with 9.15×107 m3 DRE volume. Tilocálar Sur maar crater has an elliptical shape in map view (363 m diameter east–west and 288 m diameter north–south), surrounded by individual conglomerates, sandstones, granitoids, and tuff fragments that lie on the present–day surface around the crater rim. The Tilocálar volcanic complex is interpreted as a small monogenetic volcanic field that shows an eruption history defined by a spectrum of eruptive processes determined by internal and external parameters at any given time from the four independent volcanic centers. • Four monogenetic centers are characterized as the Tilocálar monogenetic volcanic field. • Magmatic effusive, magmatic explosive, and phreatomagmatic activity is evidenced. • The Monturaqui-Negrillar-Tilopozo aquifer is associated with the Tilocálar Sur maar. • The El Maní dome with flow–mingled textures indicates a local transtensive regime. • A local transtensive regime is proposed for the Tilocálar volcanoes emplacement. [ABSTRACT FROM AUTHOR]

Cerro Tujle is an isolated Quaternary maar located 21 km south-east of the Salar de Atacama basin. It is situated at 3,554 m a.s.l., on the top of the Cordón de Tujle ridge forming a north-south striking morphological element in the Central Volcanic Zone of the Andes, in northern Chile. The material erupted at Cerro Tujle lies over the Tucúcaro Ignimbrite (3.2 ± 0.3 Ma), covering the whole area. The origin of the magma source, as well as the evolution and control of the volcanic eruptive styles, were determined by fieldwork, stratigraphic, morphometric, textural (density and vesicularity), petrographic, and geochemical analyses. The Cerro Tujle maar features an elliptical crater (333 × 279 m wide in east-west and north-south directions, respectively) surrounded by lava flow and tephra deposits. The total Dense Rock Equivalent volume of the products was calculated in 1.53 × 105 m3, and mainly correspond to andesites (58.62–59.80 wt% of SiO 2). The lava flow can be categorized in at least two types: i) brown-red and green-to-gray andesites located on the north-northwestern flank of the crater, and ii) black andesites with felsic rock clasts distributed around the crater underlying the other lavas. In contrast, the pyroclastic deposit displays breccias of juvenile pyroclasts with xenoliths of rhyolitic composition. These felsic clasts suggest magma assimilation with a shallow magma reservoir during a relatively fast ascent of the magma. This is evidenced by disequilibrium textures in mineral levels, such as reaction rim, and skeletal and sieve textures of the phenocrysts. The field evidence and results of the different analyses suggest a change in the eruptive style from effusive to explosive. This transition is associated with a decrease of the magma flux and a withdrawal of magma below the groundwater table, which has produced a phreatomagmatic eruption by magma-water interaction. • The field relationships between lava flow emission and pyroclastic surge deposit. • Changing eruptive styles in intermediate volcanism. • The hydromagmatic explosive eruptions are not uncommon in the Altiplano-Puna region, northern Chile. [ABSTRACT FROM AUTHOR]

Maar volcanoes are monogenetic landforms whose craters cut below the pre-eruptive surface and are surrounded by a tephra ring. Both the maar crater and the surrounding tephra rim deposits are typically formed due to magma–water explosive interactions. Northern Chile is located in the Central Volcanic Zone of the Andes where, in literature, 14 maars have been recognized as parasite (6) and individual (8) volcanoes. Amongst these individual maars, 3 of them, namely the Tilocálar Sur, Cerro Tujle, and Cerro Overo volcanoes, are not related to calderas and were emplaced <1 Ma ago by magmatic explosive-effusive and phreatomagmatic eruptions. Based on the evolution and control of the volcanic eruptive styles of these three maars, which have been determined in previous research through fieldwork, stratigraphic, morphometric, textural (density and vesicularity), petrographic, and geochemical analyses, a set of key features that favor a prediction of the emplacement location of maar volcanoes in Central Andes, northern Chile are proposed. The set of features that permit and favor the growth mechanisms for maar formations corresponds to (i) a compressive tectonic setting (e.g., ridge structures), (ii) groundwater recharge (e.g., snowmelt and seasonal rainfall), (iii) the lithological setting (e.g., layers of low permeability), (iv) the presence of aquifer and/or endorheic basins (e.g., lakes or salars), and (v) a period of stress relaxation that permits magma ascent to the surface in volcanically active areas. Considering these characteristics, it is possible to identify places where phreatomagmatic eruption can occur. If the magma ascent flux is lower than the groundwater flux, this can lead to a phreatomagmatic eruption because of groundwater coming into contact with the magma. These eruptive features evidence internal—and external—factors that play an essential role in the transition from explosive-effusive magmatic to phreatomagmatic volcanic eruption styles during the same eruptive period that is one of the biggest challenges in volcanic hazard evaluations. Although, in this contribution, a set of features that permit and favor the growth mechanisms for a prediction of the emplacement location of maars in northern Chile is proposed, these considerations could also be applied to identify potential locations in other parts of the world where magma–water interaction eruption could occur. Therefore, this approach could be useful in the prediction of hydromagmatic volcanic eruptions and, thus, in mitigating the impact of volcanic hazard for the inhabitants of the surrounding areas. [ABSTRACT FROM AUTHOR]

UV cameras have been used for over a decade in order to remotely sense SO2 emission rates from active volcanoes, and to thereby enhance our understanding of processes related to active and passive degassing. Whilst SO2 column density retrievals can be more accurate/sophisticated using alternative techniques (e.g., Differential Optical Absorption Spectrometer (DOAS), Correlation Spectrometer (COSPEC)), due to their higher spectral resolutions, UV cameras provide the advantage of high time-resolution emission rates, a much greater spatial resolution, and the ability to simultaneously retrieve plume speeds. Nevertheless, the relatively high costs have limited their uptake to a limited number of research groups and volcanic observatories across the planet. One recent intervention in this regard has been the introduction of the PiCam UV camera, which has considerably lowered instrumental cost. Here we present the first data obtained with the PiCam system from seven persistently degassing volcanoes in northern Chile, demonstrating robust field operation in challenging conditions and over an extended period of time, hence adding credence to the potential of these units for more widespread dissemination to the international volcanic gas measurement community. Small and weak plumes, as well as strongly degassing plumes were measured at distances ranging 0.6–10.8 km from the sources, resulting in a wide range of SO2 emission rates, varying from 3.8 ± 1.8 to 361 ± 31.6 td−1. Our acquired data are discussed with reference to previously reported emission rates from other ground-based remotely sensed techniques at the same volcanoes, in particular considering: resolution of single plume emissions in multi-plume volcanoes, light dilution, plume geometry, seasonal effects, and the applied plume speed measurement methodology. The main internal/external factors that influence positive/negative PiCam measurements include camera shake, light dilution, and the performance of the OpenCV and control points post processing methods. A simple reprocessing method is presented in order to correct the camera shake. Finally, volcanoes were separated into two distinct groups: low and moderate SO2 emission rates systems. These groups correlate positively with their volcanological characteristics, especially with the fluid compositions from fumaroles. [ABSTRACT FROM AUTHOR]

El País is a monogenetic lava flow field located 16 km southeast of Peine town in the Altiplano-Puna area, Antofagasta region, Chile. El País is a monogenetic lava flow field located 16 km southeast of Peine town in the Altiplano-Puna area, Antofagasta region, Chile. El País is composed by lava flows of small-to-moderate volumes, which are fed from individual point sources unassociated with a central volcano of large-volume (stratovolcano) typical of the Andean arc. This lava flow field was emplaced in an area dominated by thin-skinned deformation under a compressive tectonic regime, where multiple volcanic centers (monogenetic and polygenetic volcanoes) have been developed. The volumetric and chemical evolutions were determined by fieldwork, stratigraphic, morphometric, textural (density and vesicularity), petrographic, and geochemical analyses. El País can be divided into three principal mafic lava flows such as Northern-, Main-, and Western-lava flows, which display an E-W orientation. Besides, at least eight ephemeral vents were identified as small erosion remnants of lava emitting point-sources. The identified vents are principally aligned in an ENE-WSW direction, east of the Main lava flow. It is inferred that El País was emplaced near-simultaneously above two ignimbrite sheets: Tucúcaro Ignimbrite (3.2 Ma) and Patao Ignimbrite (3.1 Ma). Stratigraphically, the Main lava flow has a surface texture with strong similarities to an ʻaʻā lava flow, composed of three unique layers well distinguishable in the field such as i) Basal, ii) Top auto-breccia, composed of sub-angular scoriaceous and dense clasts in an oxidized matrix, and iii) A single core between both auto-breccias, composed of dense lavas, exhibiting multiple cooling jointing, such as vertical to platy jointing. The advanced stage of erosion since the formation of El País is evidenced by the poorly preserved lava flows (flat morphology), upper auto-breccia layer, and the presence of large sub-angular blocks of lava (vesicular and dense) along the axis of the lava flows. The eruptive products are geochemically basaltic andesite (Main lava flow and ephemeral vents) and andesite (specifically in the Northern lava flow), making the lava flow field one of the most mafic in the broader region. The lava presents a glomeroporphyric texture, showing at least three different glomerocrysts: i) Plagioclase + clinopyroxene having reabsorption boundaries, ii) Clinopyroxene with reabsorption boundaries, and iii) Plagioclase with sieve-texture. The groundmass is principally composed of glass, plagioclase microlites with a low orientation preference, and opaque minerals (magnetite). This study helps understand the development of dispersed-monogenetic-volcanism (e.g., Tilocálar complex and Cerro Tujle maar), and its relationship with neighboring polygenetic volcanism (e.g., Toloncha stratovolcano) in the Central Volcanic Zone of the Andes, northern Chile. • Different vent location during effusive eruption in lava flow field context. • Ascent rate of basic and intermediate volcanism related with deep source and low magma supply. • Erosion process in dessert climate. [ABSTRACT FROM AUTHOR]

A detailed study on the mineralogy and chemistry of fumarolic deposits with a focus on metals and metalloids is presented. Two active volcanoes in northern Chile, Guallatiri and Lastarria, are characterised by vigorous and persistent fumarolic activity and the formation of zoned fumarolic deposits. Twelve minerals were identified in the studied deposits by X-ray diffraction: anhydrite, barite, gypsum, rhomboclase, orpiment, pyrite, galena, cristobalite, quartz, magnetite, sassolite, and native sulphur. Chemical analyses revealed the presence of 30 chemical elements, including metals and metalloids such as As, Hg, Pb, Sb, Te, and Tl. Backscattered-electron imaging revealed four types of rock textures in the fumarolic deposits: i) massive and poorly vesiculated, ii) highly vesiculated, iii) clastic-like, and iv) flow-like. Micro-chemical analyses showed the presence of cinnabar nataliyamalikite and unidentified mineral assemblages of As S, Te S, Pb S, Hg S, Tl I, and Tl-I-Pb compositions. Based on colour, outlet gas temperature, mineralogy, and chemistry, four distinct zones of fumarolic deposits are identified. (1) Grey zone: sulphide and silicate dominant with minor native elements, high concentrations of Pb and As, and a clastic-like texture (gas outlet temperature > 265 °C). (2) Red zone: sulphide and silicate dominant with minor oxides and native elements, small As, Pb, Tl, I, and Te minerals, and predominance of a flow-like texture (200–280 °C). (3) Yellow-orange zone: dominated by native sulphur and minor borates and sulphur with small As-, Sb-, Hg-, and I-containing minerals, massive and vesiculated texture (80–200 °C). (4) Yellow-white zone: formed by native sulphur, minor borates and As-rich zones, usually displaying a vesiculated texture (<100 °C). • Mineralogy and chemistry of fumarolic deposits of Guallatiri and Lastarria volcanoes are investigated. • Native sulphur is the most common mineral in fumarolic deposits. • Rare As S, Te S, Pb S, Hg S, Tl I, and Tl-I-Pb mineral assemblages were found. • A detailed description of northern Chilean fumarolic deposits is provided. [ABSTRACT FROM AUTHOR]