Copahue Research Articles

Eruption Forecasting Model for Copahue Volcano (Southern Andes) Using Seismic Data and Machine Learning: A Joint Interpretation with Geodetic Data (GNSS and InSAR)

Abstract Anticipating volcanic eruptions remains a challenge despite significant scientific advancements, leading to substantial human and economic losses. Traditional approaches, like volcano alert levels, provide current volcanic states but do not always include eruption forecasts. Machine learning (ML) emerges as a promising tool for eruption forecasting, offering data-driven insights. We propose an ML pipeline using volcano-seismic data, integrating precursor extraction, classification modeling, and decision-making for eruption alerts. Testing on six Copahue volcano eruptions demonstrates our model’s ability to identify precursors and issue advanced warnings pseudoprospectively. Our model provides alerts 5–75 hr before eruptions and achieving a high true negative rate, indicating robust discriminatory power. Integrating short- and long-term data reveals seismic sensitivity, emphasizing the need for comprehensive volcanic monitoring. Our approach showcases ML’s potential to enhance eruption forecasting and risk mitigation. In addition, we analyze long-term geodetic data (Interferometric Synthetic Aperture Radar and Global Navigation Satellite System) to assess Copahue volcano deformation trends, in which we notice an absence of noteworthy deformation in the signals associated with the six small eruptions, aligning with their small magnitude.

Seismic Event Detection in the Copahue Volcano Based on Machine Learning: Towards an On-the-Edge Implementation

This study focused on seismic event detection in a volcano using machine learning by leveraging the advantages of software/hardware co-design for a system on a chip (SoC) based on field-programmable gate array (FPGA) devices. A case study was conducted on the Copahue Volcano, an active stratovolcano located on the border between Argentina and Chile. Volcanic seismic event processing and detection were integrated into a PYNQ-based implementation by using a low-end SoC-FPGA device. We also provide insights into integrating an SoC-FPGA into the acquisition node, which can be valuable in scenarios where stations are deployed solely for data collection and holds the potential for the development of an early alert system.

One decade of b-value variations from volcano-tectonic seismicity as an early indicator of episodes of crisis in a volcano: the case of Copahue, Southern Andes

Volcanoes can enter in episodes of unrest, which might end later in an eruption, with little warning. They are normally produced due to the inner dynamics of the volcano, but can also be triggered by external earthquakes. To detect these periods early, it becomes crucial to understand the dynamics of the different structures (such as fault systems) of the volcano, as they can act as magma pathways and can also generate instabilities on it. In this article we study the seismicity of Copahue (central-south Chile), which sits atop a complex system of faults, and was importantly affected by the 2010 Mw 8.8 Maule earthquake. We focused ourselves in the temporal variations of the b-value of the Gutenberg-Richter law during the 2012–2022 period. During this timeframe the volcano had a series of crises, which led to seven eruptive phases. Our results show that the system does exhibit signs of a future unrest phase weeks to months before there is a change on its alert level, and they are mostly linked to the activity of a N-S fault zone, located not beneath the main crater of Copahue, but around 10 km to the East. Most of the crises start after drops in the b-value of this structure, with sudden variations in b-value being also noticeable as a response to the 2015 Mw 8.3 Illapel earthquake. Our results show a correlation between instances of fluid injection and release in the relevant structures of an active volcano with the variations of the b-value. This allow us to use the temporal variations of the b-value as a tool to anticipate the inner dynamics of the system, particularly when there is a strong structural control on it, such as in the case of Copahue. We also found out that the influence of the 2010 Mw 8.8 Maule earthquake was long-lived, affecting mostly the structures that later destabilized the volcano for the most part of a decade, therefore enhancing magma injection into the whole system. This seems to have changed since 2021, which might indicate a waning in the influence of the megathrust earthquake in Copahue volcano.

Characterizing polarized frequencies of tremor episodes at Copahue volcano (Southern Andes): A case study

The characterization of dominant frequencies is essential for tracking significant temporal variations during and between tremor episodes. In this work, we proposed a method for quantifying the dominant frequencies and their attributes. We applied it to characterize three tremor episodes recorded several hours before ash emissions at Copahue volcano during June–August 2020. The method consisted in (i) extracting dominant peaks (relative maximum in successive PSD) and their polarization attributes: polarization degree, rectilinearity, and polarization angles; and (ii) extracting dominant frequencies (i.e., relative maximums in the PDF of dominant peaks) and their polarization attributes. We applied the method at three stations located at 4.5, 9.5, and 11 km from the crater vent to investigate how the characteristics for dominant frequencies change among the stations. We found linearly polarized peaks in the three stations whose azimuth coincides with crater direction. The station closest to the crater (NAN5) recorded linearly polarized frequencies above 3.0 Hz. The time evolution of dominant peaks suggests that different sources compose the seismic tremor. Our results represent a forward step in the understanding of eruptive tremors of Copahue, being a clear example that their implementation at other volcanoes can improve the monitoring tasks.

Emplacement and eruptive style of high-grade ignimbrites from fissure vents: The Las Mellizas Ignimbrite, Caviahue-Copahue volcanic complex, southern Andes

The Pliocene to Recent Caviahue – Copahue volcanic complex is located in the Southern Volcanic Zone of the Andes. The Las Mellizas Ignimbrite is widely distributed in the intra-caldera region of the previously formed Caviahue caldera. Detailed field work led us to identify four facies associations for Las Mellizas Ignimbrite and to characterize the pyroclastic facies as dominantly vitrophyric, eutaxitic and rheomorphic, with limited occurrences of welded agglomerates and lithic breccias. Pyroclastic dykes with subvertical eutaxitic fabric were found and interpreted as fissure vents of this ignimbrite. Their orientations follow either the southern Caviahue caldera rim, or approximately the current extension direction as determined by previous neotectonic studies. Thermobarometry and hygrometry estimations were carried out based on compositional analyses of minerals (plagioclase, ortho- and clinopyroxenes, FeTi oxides) and glass. We interpret that Las Mellizas Ignimbrite was deposited from high-temperature and concentrated pyroclastic density currents, formed by almost fully collapsed low eruptive columns (pyroclastic fountaining). Low pre-eruptive pressures (0.04–0.06 GPa) and moderate water content (2.0–3.4 wt%) plus the low crystallinity of the magma (<10 vol% of phenocrysts) points to a shallow magma chamber and shallow fragmentation level, which is also supported by lithic clast composition. The eruption trigger is interpreted as mainly due to magmatic processes, and aided by tectonic activity. The presence of topographic scarps, outcrops distribution and stratigraphic discontinuities north of the Copahue volcano, in addition to co-ignimbritic lithic breccias, suggest that a small collapse may have occurred, nested on the western Caviahue caldera rim. In this context, the fissure vents represent peripheral extra-caldera pyroclastic conduits.

Long-duration seismicity and their relation to Copahue volcano unrest

Understanding seismic tremor wavefields can shed light on the complex functioning of a volcanic system and, thus, improve volcano monitoring systems. Usually, several seismic stations are required to detect, characterize, and locate volcanic tremors, which can be difficult in remote areas or low-income countries. In these cases, alternative techniques have to be used. Here, we apply a data-reduction approach based on the analysis of three-component seismic data from two co-located stations operating in different times to detect and analyze long-duration tremors. We characterize the spectral content and the polarization of 355 long-duration tremors recorded by a seismic sensor located 9.5 km SE from the active vent of Copahue volcano in the period 2012–2016 and 2018–2019. We classified them as narrow- (NB) and broad-band (BB) tremors according to their spectral content. Several parameters describe the characteristic peaks composing each NB episode: polarization degree, rectilinearity, horizontal azimuth, vertical incidence. Moreover, we propose two coefficients C_P and C_L for describing to what extent the wavefield is polarized. For BB episodes, we extend these attributes and express them as a function of frequency. We compare the occurrence of NB and BB episodes with the volcanic activity (including the level of the crater lake, deformation, temperature, and explosive activity) to get insights into their mechanisms. This comparison suggests that the wavefield of NB tremors becomes more linearly polarized during eruptive episodes, but does not provide any specific relationship between the tremor frequency and volcanic activity. On the other hand, BB tremors show a seasonal behavior that would be related to the activity of the shallow hydrothermal system.Graphical

A reinterpretation of pyroclastic density current deposits at Copahue volcano, Andean Southern Volcanic Zone, Argentina-Chile

Pyroclastic density currents (PDCs) are one of the most dangerous volcanic phenomena. The correct interpretation and mapping of PDC deposits in the volcano record is important to establish the eruptive style and play a fundamental role in hazard assessment and risk management. The Copahue volcano is an active intermediate volcano of the Southern Volcanic Zone of the Andes (Argentina-Chile) that presents fragmentary evidence of explosive activity during its evolution, with unusual minor PDC deposits. The recorded historic eruptions were mainly phreatomagmatic due to the presence of a crater lake. In this study, four key deposits previously interpreted as PDC products corresponding to different stages of the Copahue volcano evolution (Pleistocene, Holocene, and Historic times) are analyzed and this origin is discussed: (i) A Pleistocene reddish succession located in the northeast flank of the volcano formed by stretched bombs in a coherent lava is interpreted as clastogenic lavas; (ii) a series of proximal bedded volcaniclastics deposits of Pleistocene age are interpreted as redeposition of hyaloclastic fragments from syn-eruptive subglacial meltwater flows associated with subglacial eruptions; (iii) a distal Holocene deposit located ~12 km east of the active crater consist mainly in fine-sized clasts forming aggregates is reinterpreted as a sedimentary (lacustrine) deposit with volcaniclastic input; and, (iv) a historic whitish-grey clastic deposit located on the eastern flank is considered a product of a mixed avalanche generated during the 1992–1995 activity. Consequently, the PDC occurrence during the Copahue volcano evolution is less than previously thought. Large PDCs are unlikely in the future and their influence area would be reduced near the active crater as observed in recent eruptions. Flows triggered by the melting of snow/ice during volcanic activity and sudden drainage of the crater lake appear to be a more likely potential hazard that should be considered during risk assessment.

An analysis of volcanic SO2 and ash emissions from Copahue volcano

During 2016, Copahue volcano (Neuquén, Argentina) made several eruptions and emitted ash and gases. This paper presents an analysis of the volcanic plume using dispersion models, remote sensor data, and analysis of sedimentary ash collected at the Caviahue Health Center from early October to 21st December 2016. Water-soluble elements contained in volcanic ash leachates were quantified. We have carried out a qualitative comparison of HYSPLIT dispersion simulations with SO2 and aerosol data obtained from OMI and OMPS sensor on board of AURA and SUOMI NPP satellites, as well as between modeled concentrations and sampled surface sediments. Good agreement was observed between gas dispersion plumes from HYSPLIT and total column SO2 values, as well as between volcanic ash plumes and satellite aerosol indices.The average SO2 emission rate in the analyzed events was 985.7 ± 492.9 t/d and the average emission rate of ash 2.6 103 kt/d (2.9 104 kg/s). In situ observations of ash deposition rates peaked at 0.23 g/h on 30th November. The average measured deposition rate from 1st October to 21st December was 0.12 g/h, consistent with modeled values. The geochemical analysis of ash leachate showed major content of sodium (Na), calcium (Ca) and magnesium (Mg) with 207.8 mg/kg, 209.5 mg/kg, and 195.3 mg/kg, respectively. Concentrations sulfate, chlorides, and fluoride anions were 990.7 mg/kg, 352.34 mg/kg, and 129.15 mg/kg, respectively. The SO2/HCl molar ratio was 1.05. In addition, traces of As, Cr, Hg, Mo, Pb, and Se were detected in concentrations ranging from 0.2 mg/kg to 6.0 mg/kg.

Analysis of thermal anomalies at Copahue Volcano between October 2011 and the December 2012 eruption with MODIS

Copahue volcano is an active stratovolcano located in the Southwest of the Agrio-Caviahue depression in the Province of Neuquén at the border between Argentina and Chile, and the most recent eruptive activity involved five cycles between 1992 and 2016. The Moderate Resolution Imaging Spectroradiometer (MODIS) is an instrument onboard the satellites Terra and Aqua that provides, on average, four images per day and has channels centered at 4 μm and 12 μm that are useful for detecting volcano temperature anomalies. In this work, we evaluated the normalized temperature index (NTI) as implemented by MODVOLC and the radiance recorded by MODIS at 4 μm as measures of precursory volcanic activity between October 2011 and January 2013, with a special focus on the December 2012 eruption. We evaluated the thermal anomalies identified by MODVOLC based on a global threshold of −0.8 and observed that they were namely syn- or post-eruptive and mostly correlated with the presence of incandescence material related to Strombolian activity. The global nighttime threshold was adapted to the local context of Copahue and we observed that a threshold of −0.875 is a more suitable value for the examined period. An analysis of time series of the NTI and of the radiance at 4 μm based on 116 MODIS images, resulted in that the adapted threshold allowed the detection of anomalies undetected by the global value. The anomalies were in either case unrelated to precursory activity but correlated with surface expressions of activity such as the emission of volcanic ash, volcano degassing, and the ejection of ballistic and incandescent material. The knowledge on the chronology of activity prior to and during the eruption could be improved, as regards the thermal behavior of the volcano in relation also to geochemical, deformation, and seismic signals. The replication of this kind of analysis in other periods of activity at Copahue and other volcanoes, the evaluation of other algorithms and the incorporation of data acquired by other satellite instruments are necessary to improve our knowledge on the temperature behavior of volcanoes before and during periods of unrest. This would ultimately contribute towards the improvement of volcano monitoring capabilities in volcanic areas.

Late Pleistocene subglacial fissure-related volcanism at Caviahue-Copahue Volcanic Complex (37° 51° S, 71° 05’ W), South Volcanic Zone

The Caviahue-Copahue Volcanic Complex (CCVC, 37° 51’ S-71° 05′ W) is located in the central segment of the South Volcanic Zone, ~30 km eastward from the main Andean volcanic arc. Within a complex tectonic setting, it has developed under the influence of the northern transtensional Liquiñe-Ofqui Fault Zone, to the south and the Copahue-Antiñir Fault Zone to the northeast. The onset of volcanic activity within Caviahue volcano-tectonic depression has been dated at Ar/Ar 125 ± 9 ka and it is represented by lava flows and ignimbrites of Las Mellizas Formation. Copahue volcano has a very well documented historical eruptive record, encompassing 13 eruptive cycles in the last 260 years. On the contrary, volcano stratigraphy during Late Pleistocene and pre-historic times is poorly constrained, mainly due to the lack of reliable radiometric data. Based on the peculiar morphology and cooling-fracture systems, lavas that crop out along Dulce, Jara and NE Agrio river valleys have been included in a new stratigraphic unit, here named as Río Dulce Formation. A subglacial emplacement is proposed taking into account the evidence of ice-confinement, provided by the flat-topped and steep-sided lava domes/flows and dammed lava flows. In addition, melt water-magma interaction is supported by conspicuous fine columnar-jointing and closely spaced curved bands with plumose structures, well-developed pseudopillow fracture systems, platy and hackly fractures and cube-jointed entablature-bearing lava flows. The basaltic andesites (SiO2= 55–57%) are porphyritic, with ~30–40% of sieved plagioclase, two pyroxenes and olivine, set in a glassy groundmass. Lava vent distribution and primary anisotropy planes orientation, in coincidence with WNW-ESE and NE-SW trending faults, lineaments and fault scarps, document a first-order structural control on the volcanic emplacement. Although undated, this study can contribute to understanding the timing of glacial fluctuations during Late Pleistocene. Furthermore, it has implications on hazard assessment since it highlights that the evolution of the CCVC has experienced alternating fissure and central eruptive style, likely related to the dynamics of the magma-plumbing system, as suggested by geophysical evidence of unrest.

Low-Energy Fragmentation Dynamics at Copahue Volcano (Argentina) as Revealed by an Infrasonic Array and Ash Characteristics

Ash-rich eruptions represent a serious risk to the population living nearby as well as at thousands of kilometers from a volcano. Volcanic ash is the result of extensive magma fragmentation during an eruption, and it depends upon a combination of magma properties such as rheology, vesicularity and permeability, gas overpressure and the possible involvement of external fluids during magma ascent. The explosive process generates infrasonic waves which are directly linked to the outflow of the gas-particle mixture in the atmosphere. The higher the overpressure in the magma, the higher should be the exit velocity of the ejected material and the acoustic pressure related to this process. During violent eruptions, fragmentation becomes more efficient and is responsible for the extensive production of ash which is dispersed in the atmosphere. We show that the phase of intense ash emission that occurred during March 2016 at Copahue volcano (Argentina) generated a very low (0.1 Pa) infrasonic amplitude at 13 km, raising a number of questions concerning the links among acoustic pressure, gas overpressure and efficiency of magma fragmentation. Infrasound and direct observations of the eruptive plume indicate that the large quantity of ash erupted at Copahue was ejected with a low exit velocity. Thus, it was associated with eruptive dynamics driven by a low magma overpressure. This is more evident when infrasonic activity at Copahue is compared to the moderate explosive activity of Villarrica (Chile), recorded by the same array, at a distance of 193 km. Our data suggest a process of rigid fragmentation under a low magma overpressure which was nearly completely dissipated during the passage of the erupting mixture through the granular, ash-bearing crater infilling. We conclude that ash released into the atmosphere during low-energy fragmentation dynamics can be difficult to monitor, with direct consequences for the assessment of the related hazard and management of eruptive crises.

Structural control on shallow hydrogeochemical processes at Caviahue-Copahue Volcanic Complex (CCVC), Argentina

The Caviahue-Copahue Volcanic Complex (CCVC) hosts one of Argentina's most important geothermal systems. To provide new insights into origin, circulation, and residence time of fluids, the chemical and isotopic composition (3He/4He, δ2H-δ18O in H2O; δ13C-δ18O in CO2; 87Sr/86Sr) of thermal waters was measured together with the 3H and 14C activities. Water samples were collected from hot springs (LM, TC, LMM, CB and AF) representing the five major thermal zones of the CCVC and assumed to be steam-heated meteoric waters, and a well condensate (COP-2). The LMM, CB, and AF chemical composition and 87Sr/86Sr ratios show that water chemistry is acquired locally from exchange with volcanic rocks (Sr, SiO2, among others) and from steam (H2S). Two surface geothermal manifestations (LM and TC), along with the well condensate, COP-2, contain a higher contribution of deep-originating fluids, with 87Sr/86Sr indicating possible contribution from deep-seated granitoids or sediments from the underlying basement. Radiocarbon-based residence times indicate ages ranging between 13,540 and 17,520 yrs. BP, representing the minimum age for the geothermal reservoir waters. Tritium is mainly absent in hot spring waters except for LMM and CB where the activity is close to the detection limit. This indicates a minimum age older than 70 yrs. for the water circulating in the shallow circuit. This result suggests that shallow meteoric water have a more complex and/or deeper circuit, resulting in older residence times. Helium isotopes in the CCVC span a wide range, from a pure mantle-derived value, of 8.35Ra, to a more crustal radiogenic signature, of 4.6Ra. The spatial variation is explained by associating the geochemical data with the geological context, which includes the distribution of fault-fracture meshes and different sources of magmatic volatiles underlying the Copahue volcano. The first order control on helium isotope signatures observed in this study seems to be dominated by the degree of crustal assimilation of the magmatic sources, which is in turn controlled by the local arrays of faults.

Seismic evidence of the active regional tectonic faults and the Copahue volcano, at Caviahue Caldera, Argentina

Understanding interactions between tectonic faults and a nearby active volcano is often realized by combining seismic and field observations. A good example of such an interaction is the Caviahue caldera. It is located in an intra-arc extensional pull-apart basin, within a transition zone joining the northern part of the right-lateral strike-slip Liquiñe-Ofqui Fault System and the thrust-fault Antiñir-Copahue fault zone. Most of the active volcanoes in South Chile are related to the Liquiñe-Ofqui Fault System. Some faults located inside the Caviahue caldera were described with reverse mechanisms by some studies whereas they were found to be normal by others. In order to discriminate the actual focal mechanisms, two seismic clusters that occurred in 2017 and 2018 inside the Caviahue rectangular caldera, close to the active Copahue volcano, were studied. Earthquakes (520) were located; focal mechanisms (56) were determined from which an average seismic moment tensor was calculated. The locations and focal mechanisms of the earthquakes allow splitting the seismicity into two main regions, one of tectonic origin (with strike-slip faults) and another one of volcanic origin (with normal faults). The first seismic cluster is located close to Caviahue village, with strike-slip focal mechanisms, in an NNE direction as the nearby Liquiñe-Ofqui Fault strikes. The other part of the seismicity is located close to the northeastern structures of Copahue volcano, in the hydrothermal zone of Anfiteatro, Termas de Copahue, and Maquinitas. It is oriented in an NE direction and is composed of earthquakes with normal focal mechanisms, not reverse as postulated in past studies. The active Copahue volcano lies in the SW prolongation of these normal faults, in agreement with the tectonics of the Caviahue caldera. Then, the two nearby seismic clusters reveal both a tectonic origin, with strike-slip focal mechanisms compatible with the Liquiñe-Ofqui Fault System, and a hydrothermal origin with normal focal mechanisms, compatible with the hydrothermal system of the Copahue active volcano.

Desarrollo de Técnicas de Muongrafía para Estudios Densitométricos de Objetos de Importancia Estratégica

La muongrafía es una técnica de prospección no destructiva que permite la determinación de la estructura interna de grandes estructuras tanto naturales como artificiales, por ejemplo volcanes. Esto es posible al construir una imagen con base en la absorción diferencial del flujo direccional de muones atmosféricos producto de la interacción de rayos cósmicos con la atmósfera. Este trabajo doctoral es desarrollado con el propósito principal de aportar en el avance de la muongrafía como técnica de prospección en Geofísica. El trabajo se compone de dos lineas de trabajo, una experimental y una teórica. La experimental se basa en el desarrollo de un prototipo de detector de astropartículas con base en centelladores plásticos y fotomultiplicadores, para esto se usa una electrónica de adquisición desarrollada para el proyecto AMIGA en el Observatorio Pierre Auger y materiales centelladores de plástico. La segunda linea de trabajo trata del estudio del detector y las estructuras de investigación a través de simulaciones computacionales y modelos teóricos. Durante los dos primeros años se completaron los créditos de cursos solicitados por el doctorado, Ademas se trabajó en el estudio de la respuesta de la electrónica, los pulsos, técnicas de análisis de datos y el acople de fotomultiplicadores con los centelladores. Gracias a esto se avanzo en el desarrollo del prototipo y se investigo la posibilidad de incrementar la resolución espacial a través de la detección sincrónica usando electrónicas conectadas al mismo centellador. Actualmente iniciamos el trabajo en los modelos computacionales, estamos estudiando e investigando con respecto a los candidatos a objetos de estudio, destacando el volcán Copahue, volcán Peteroa y la posibilidad de realizar mediciones bajo tierra.

Unraveling the timing of the Caviahue depression, Andean Southern Volcanic Zone: insights from the sedimentary infill

The Caviahue–Copahue volcanic complex in the Southern Volcanic Zone of the Andes is composed of the Pliocene–Pleistocene Caviahue depression and the active Copahue volcano. This volcanic complex is located in a zone of profuse volcanic and tectonic activity, and thus, the origin of the depression includes both tectonic and volcanic hypothesis (e.g., formation of a collapse caldera and a pull-apart basin). According to current knowledge, the oldest rocks filling the depression are lavas and ignimbrites of the Pleistocene Las Mellizas Formation. However, clastic sedimentary deposits underlying this unit have been recognized. Here, we document the characteristics of these deposits at the south shore of the Caviahue lake using field data and digital outcrop models (DOM). We have concluded that the deposits are deltaic and alluvial in origin and made up by a prodelta/distal deltaic front, delta front deposits, delta plain sediments and alluvial deposits. An unconformity separates the deltaic deposits from overlying alluvial deposits, indicating the decrease in the stratigraphic base level probably associated with a sudden coarse-grained clastic input and a drop in the lake level. Our study has implications on the timing and evolution of the Caviahue depression and indicates that the depression precedes the Las Mellizas Formation. Thus, Las Mellizas ignimbrite should not be interpreted as the main unit related to the Caviahue caldera as it has been proposed by some authors. If the depression had indeed been formed by a collapse caldera, this event would be previous to the described sediments.

Defining Culture Conditions for the Hidden Nitrite-Oxidizing Bacterium Nitrolancea.

Nitrification is a key process for N-removal in engineered and natural environments, but recent findings of novel nitrifying microorganisms with surprising features revealed that our knowledge of this functional guild is still incomplete. Especially nitrite oxidation – the second step of nitrification – is catalyzed by a phylogenetically diverse bacterial group, and only recently bacteria of the phylum Chloroflexi have been identified as thermophilic nitrite-oxidizing bacteria (NOB). Among these, Nitrolancea hollandica was isolated from a laboratory-scale nitrifying bioreactor operated at 35°C with a high load of ammonium bicarbonate. However, its distribution remains cryptic as very few closely related environmental 16S rRNA gene sequences have been retrieved so far. In this study, we demonstrate how such thermophilic NOB can be enriched using modified mineral media inoculated with samples from a wastewater side-stream reactor operated at 39.5°C. Distinct cultivation conditions resulted in quick and reproducible high enrichment of two different strains of Nitrolancea, closely related to Nl. hollandica. The same cultivation approach was applied to a complex nitrite-oxidizing pre-enrichment at 42°C inoculated with biomass from a geothermal spring in the Copahue volcano area in Neuquen, Argentina. Here, an additional distinct representative of the genus Nitrolancea was obtained. This novel species had 16S rRNA and nitrite oxidoreductase alpha subunit (nxrA) gene sequence identities to Nl. hollandica of 98.5% and 97.2%, respectively. A genomic average nucleotide identity between the Argentinian strain and Nl. hollandica of 91.9% indicates that it indeed represents a distinct species. All Nitrolancea cultures formed lancet-shaped cells identical to Nl. hollandica and revealed similar physiological features, including the capability to grow at high nitrite concentrations. Growth was optimal at temperatures of 35–37°C and was strongly enhanced by ammonium supplementation. Genomic comparisons revealed that the four Nitrolancea strains share 2399 out of 3387 orthologous gene clusters and encode similar key functions. Our results define general growth conditions that enable the selective enrichment of Nitrolancea from artificial and natural environments. In most natural habitats these NOB apparently are of low abundance and their proliferation depends on the balanced presence of nitrite and ammonium, with an optimal incubation temperature of 37°C.

The glaciovolcanic evolution of the Copahue volcano, Andean Southern Volcanic Zone, Argentina-Chile

Glaciovolcanism produces distinctive features that are useful paleoclimate proxies for the distribution of past ice sheets and glacier extent. The Copahue volcano located in the Andean Southern Volcanic Zone, Argentina-Chile, is an active composite volcano known to have glaciovolcanic features such as lava bodies with glassy margins and anomalous cooling fractures. However, the emplacement conditions of these products and the influence of Pleistocene glaciations on the evolution of the Copahue volcano remains poorly understood. In this contribution, we propose a model for glaciovolcanic evolution of the Copahue volcano based on the analysis, interpretation, and mapping of its products. Ten lithofacies are described on the eastern flank of Copahue volcano exhibiting several examples of glaciovolcanism. The evolution of the Copahue volcano can be divided into two main sequences: the Ancient Sequence (S1) and the Young Sequence (S2), separated by a major erosive phase. The S1 (early-middle Pleistocene-late Pleistocene) consists of an initial subaerial effusive stage followed by a major glaciovolcanic stage, during which a thick ice cap existed and the edifice grew beneath an englacial lake with the eventual formation of a lava-fed delta. The S2 (late Pleistocene-Present) is defined by mainly effusive activity during periods of glacial advance and retreat recorded by an alternation of unconfined subaerial lavas and ice-confined lavas. The evolution of the Copahue volcano therefore indicates two glaciations in the Copahue-Caviahue area during the late Pleistocene, in contrast to a single glaciation. Based on the glacial history in the area we associate the first glaciation with the end of Marine Isotope Stage 3 (57–29 ka) and/or the Last Glacial Maximum period (26.5–19.0 ka), and the second less-extensive glacial period with the Antarctic Cold Reversal (14.5–12.9 ka).

A Deeper Look into the Biodiversity of the Extremely Acidic Copahue volcano-Río Agrio System in Neuquén, Argentina.

The Copahue volcano-Río Agrio system, on Patagonia Argentina, comprises the naturally acidic river Río Agrio, that runs from a few meters down the Copahue volcano crater to more than 40 km maintaining low pH waters, and the acidic lagoon that sporadically forms on the crater of the volcano, which is studied for the first time in this work. We used next-generation sequencing of the 16S rRNA gene of the entire prokaryotic community to study the biodiversity of this poorly explored extreme environment. The correlation of the operational taxonomic units (OTUs)s presence with physicochemical variables showed that the system contains three distinct environments: the crater lagoon, the Upper Río Agrio, and the Salto del Agrio waterfall, a point located approximately 12 km down the origin of the river, after it emerges from the Caviahue lake. The prokaryotic community of the Copahue Volcano-Río Agrio system is mainly formed by acidic bacteria and archaea, such as Acidithiobacillus, Ferroplasma, and Leptospirillum, which have been isolated from similar environments around the world. These results support the idea of a ubiquitous acidic biodiversity; however, this highly interesting extreme environment also has apparently autochthonous species such as Sulfuriferula, Acidianus copahuensis, and strains of Acidibacillus and Alicyclobacillus.

Thermal evolution of the Crater Lake of Copahue Volcano with ASTER during the last quiescence period between 2000 and 2012 eruptions

Active Crater Lakes are the surface expression of volcanic activity at the top of complex magmatic-hydrothermal systems. The Volcanic and Hydrothermal System Copahue is one of the most important active systems in Argentina. It lies at the border of Argentina and Chile and is very important, since the Copahue and Caviahue towns are very close and constitute important touristic resources including a ski center. The aim of this work is to improve the temperature register of the volcano and contribute towards a better understanding of the thermal behavior of the system during the quiescence period between the 2000 and 2012 eruptions. The surface temperature of the Crater Lake was estimated by using the Normalized Emissivity Method (NEM) on 70 images acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and we combined them with field measurements in order to capture the fundamental variations of the system. The analysis allowed the identification of two different thermal periods: (i) January 2001–August 2003 and (ii) December 2004–November 2011, characterized by temperature ranges of 43–50 °C and 30–45 °C, respectively. Beyond these ranges, temperature anomalies or moments of high temperature variability occurred, which corresponded to surface expressions of volcanic activity. In August 2004, the lake froze almost completely, whereas in March 2012, peak temperatures were recorded. However, a significant drop in temperature prior to the eruption of December 22, 2012, was observed, which might constitute a characteristic feature of the system. Furthermore, the Crater Lake of Copahue volcano is classified as a lake of high activity. The observations and interpretations presented constitute a useful baseline and a significant contribution towards a better understanding of the functioning of the volcano, the mitigation of volcanic hazards and the identification of volcanic unrest.

Enrichment and isolation of acid-tolerant sulfate-reducing microorganisms in the anoxic, acidic hot spring sediments from Copahue volcano, Argentina.

The geothermal Copahue-Caviahue (GCC) system (Argentina) is an extreme acidic environment, dominated by the activity of Copahue volcano. Environments characterised by low pH values, such as volcanic areas, are of particular interest for the search of acidophilic microorganisms with application in biotechnological processes. In this work, sulfate-reducing microorganisms were investigated in geothermal acidic, anaerobic zones from GCC system. Sediment samples from Agua del Limón (AL1), Las Máquinas (LMa2), Las Maquinitas (LMi) and Baño 9 (B9-2, B9-3) were found to be acidic (pH values 2.1-3.0) to moderate acidic (5.1-5.2), containing small total organic carbon values, and ferric iron precipitates. The organic electron donor added to the enrichment was completely oxidised to CO2. Bacteria related to 'Desulfobacillus acidavidus' strain CL4 were found to be dominant (67-83% of the total number of clones) in the enrichment cultures, and their presence was confirmed by their isolation on overlay plates. Other bacteria were also detected with lower abundance (6-20% of the total number of clones), with representatives of the genera Acidithiobacillus, Sulfobacillus, Alicyclobacillus and Athalassotoga/Mesoaciditoga. These enrichment and isolates found at low pH confirm the presence of anaerobic activities in the acidic sediments from the geothermal Copahue-Caviahue system.