Debris flows are among the most destructive mass-wasting processes in the southern Andes, particularly in inhabited volcanic catchments, where their dynamics remain difficult to predict. This limitation stems from the interplay among sediment availability, volcanic-edifice morphology, precipitation, snow and nival melt, and cryospheric processes, thereby hindering effective land-use planning. Our study analyses debris flows and their seasonal controls at Osorno Volcano, a representative active mountain system in southern Chile. To this end, we implement a multivariable framework that integrates geomorphological and lithological analyses to delineate functional domains of sediment generation, transport, and temporary storage; evaluates hydrometeorological and cryonival conditions using a rain-gauge network and multitemporal satellite imagery; and incorporates seismic characterisation to identify snow, rock, and/or sediment avalanches and to assess their spatial-temporal relationship with debris flows. The results support the occurrence of cascading processes, in which sediment is transferred from proximal zones to temporary storage areas and subsequently remobilised toward distal accumulation sectors. This relationship was evaluated using an empirical, conservative 7-day window, consistent with the observed duration of event cycles, but not defined as a general threshold. Overall, integrating seismic, meteorological, and cryospheric variables provides a consistent basis for understanding these processes and advancing toward predictive models aimed at anticipating mass-wasting events in mountain systems under changing hydroclimatic and cryospheric conditions.

On November 3, 2002 El Reventador volcano (Ecuador) erupted violently, causing damages near the volcano and intense ash falls in the Interandean Valley. To assess the size and style of the eruption we conducted field work to obtain tephra thickness measurements and samples in the area located similar to 50-100 km from source. The thickness data (max. 40 mm) were processed to draw an isopach map that reveals a plume dispersal to the WSW of the volcano. The ash samples underwent grain size distribution (GSD) and componentry analyses, morphometric characterization, bulk and solid density determinations, and chemical analyses. The GSD results show a single mode at 3-4 phi in the study region, indicating a finely comminuted tephra. The componentry in the deposits reveals strong density-driven fractionation of dominant poorly to highly vesiculated juvenile ash particles, and of abundant xenolithic grains. The bulk ash density was close to 1017 kg/m(3), whilst the solid (powder) density is similar to 2640 kg/m(3), and the juvenile ash bears the composition of the most differentiated products documented in historical times at El Reventador (silicic andesite: 58-59 wt% SiO2). The bulk volume of the tephra fall deposit is estimated at 80 x 10(6) m(3), and the total volume with PDC deposits at 135 x 106 m(3) (VEI4 range), while the massbased magnitude and intensity reach 4.2 and 10.8, respectively, in the range of subplinian eruptions. Accordingly, on November 3, 2002 El Reventador volcano released the largest explosive event in the whole North Volcanic Zone of the Andes since more than a century. Also, our study shows the importance of obtaining urgently ground-based data after any unexpected eruption for scenario elaboration, and that there is still room to technically improve the early characterization of such sudden explosive events.

Deep learning models have significantly improved automatic volcano-seismic event classification but struggle with previously unseen signals due to their closed-set assumption, leading to confident misclassification of external events, as seismic sensors often capture non-volcanic movements. This study ad-dresses this limitation by integrating a simple and computationally lightweight K-Nearest Neighbors (KNN)-based Out-of-Distribution (OOD) detection mod-ule into a CNN classifier, dividing the classification problem in a trade-off between the classification of in-distribution volcanic events (ID) and the iden-tification of non-volcanic events (OOD). We explored an input representation that integrates waveforms and frequency spectrum alongside spectrograms using Class Activation Maps to evaluate their impact in learning. We found that combining waveforms with spectrograms improves ID performance as well as OOD sensitivity. Experimental results on a Nevados del Chillan Vol-canic Complex database show that our approach reaches a mean accuracy of 93.5 % for non volcanic classes (correctly classified as OOD) maintaining 84.3 % for the classification of volcanic classes (ID) compared to 73.8 % with the only-spectrogram representation. These findings demonstrate that combining multi-domain feature representations with a lightweight KNN-based OOD module raises mean OOD accuracy from 73.8 % to 93.5 % while pre-serving an 84.3 % ID F1-score, thereby improving the reliability of automated volcano-seismic monitoring and provides evidence that the approach could be incorporated into deployable, multi-volcano systems after further validation on additional sites.

Debris flows represent significant threats in the Northern Andes of Patagonia (NAP). On May 1, 2019, during the winter season, an extreme hydrometeorological event of 122 mm accumulated in 24 h triggered debris flows in the Chaiguaco sector (42.1°S/72.4°W), cutting off different sections of the interregional highway with their deposits, leading southern Patagonia with no connection to the rest of Chile. The Chaiguaco debris flow represents the largest event generated at 1,240 m a.s.l. in an area heavily affected by faults. In this study, we conducted a comprehensive assessment of the factors influencing the generation of debris flows in the area, integrating field and laboratory analyses based on this representative event. The study explores three main aspects. The study explores a comprehensive interconnection of geomorphological, hydrometeorological, geotechnical, lithological, structural and mineralogical analysis, emphasizing the initiation of mass movements that can evolve into debris flows. We conclude that the Chaiguaco event represents a typical case of the NAP where an extreme hydrometeorological event in an environment where multiple factors interact triggers debris flows. We suggest addressing future studies from an interdisciplinary perspective, which can serve as baseline inputs for decision-making entities within the framework of the civil protection system of the NAP.

Very sophisticated machine learning tools are being developed for detecting P and S-waves in tectonic earthquakes, with excellent results, especially when approached from a recurrent perspective. However, their application to volcanic seismicity presents challenges due to the low magnitude, variability, and complexity of waveforms, caused by heterogeneous and anisotropic geological structures like magma chambers, rock types, and fractured zones. The proximity of sources to sensors often results in nearly simultaneous arrivals of P and S-waves. Additionally, volcanic areas are associated with high levels of seismic noise from non-volcanic sources. The specific characteristics of each volcano further necessitate adapting solutions to their unique dynamic behavior. Given these challenges, investigating signal preprocessing techniques that can improve P and S-wave detection in volcanic environments is essential. In this work, we studied seismic signals from the Nevados del Chill & aacute;n volcanic complex to evaluate whether simple yet robust information could be provided to an LSTM model for effective P and S-wave detection. Our approach achieved 94% detection rate for P-waves and 91% for S-waves within a 0.5-second error margin, for 998 P and S-waves from the test set, improving detection accuracy and noise resilience over traditional methods.

The Laguna del Maule Volcanic Complex is a post-glacial active magmatic system, located on the border between Argentina and Chile, at 36 degrees S in the Andean Range. This complex is characterized by multiple silicic eruptive centers surrounding a 23 x 16 km lake. The eruptive products range from basalts to rhyolites, with a predominance of acidic rocks in more than 50 eruptions that took place in the last 25 ka. Previous models proposed a transtensional regime during its activity, linked to a bend in a major dextral fault, the Troncoso fault. We propose that those structural models were biased by the fact that seismicity was focused on the Troncoso fault preceding 2014. Here, we present an updated seismic catalog, which provides a broader understanding of the active structures in the area. Structural analysis based on remote sensing and outcrop-scale measurements of kinematic indicators allowed us to characterize the fault kinematics and the local stress field. Integrating the structural and seismological data, we propose that the actual volcanism took place in a transpressional stress regime, consistent with the regional tectonic setting and the silicic volcanism of the Laguna del Maule Volcanic Complex.

The Southern Andes is an active zone of mass wasting processes with unknown constraints for public policies. Several conditioning factors could have an impact on the generation of debris flows, being controlled by water accumulation. This study investigates the generation of the Ñisoleufu debris flow, an active area of debris flow generation in Southern Andes, reviewing the interplay between geomorphological, geotechnical and hydrometeorological controls in debris flow dynamics, focusing on the effects of soil properties, slope characteristics and precipitation events. Our results highlight significant changes in soil moisture content on critical days associated with debris flow events. We revealed that the combination of areas with high water accumulation capacity from local runoff and slopes that capture precipitation effectively were crucial in the generation of debris flows. Areas with granular volcanic soils acted as storage mediums for water, which, coupled with decreased shear strength, facilitated debris flow initiation. The thin and fine-grained layers of glacial deposits located beneath the volcanic soil, characterized by low hydraulic conductivity, created localized accumulation zones that reinforced the storage capacity of adjacent areas, particularly in pyroclastic volcanic deposits in the release zone. The hydraulic properties of the volcanic deposits suggest that water storage capacity and high hydraulic conductivity play a critical role in rainfall-induced debris flow initiation. Additionally, we observed that the debris flow of the Ñisoleufu event has evidence of reworked lapilli-sized particles (> 5 mm), being consistent with the surface and shallow water movement that reduces the slope stability within the area. Analysis of ERA5-land dataset showed abrupt changes in soil moisture content at various depths and time periods, correlating with intense or prolonged rainfall events. These results underscore the role of geomorphological features in modulating soil moisture and thereby affecting the stability and movement of debris flows. Our results provide a comprehensive understanding of how geomorphology interacts with hydrological factors to influence debris flow behaviour in volcanic areas of the Southern Andes for the first time. Overall, the research highlights the critical role of geomorphological and hydrological factors in debris flow generation and dynamics. It emphasizes the need for incorporating detailed soil and slope characteristics into models for predicting debris flow risks. By understanding the combined effects of water accumulation, soil properties, and slope dynamics, this study contributes valuable insights into managing and mitigating debris flow hazards in vulnerable regions. These findings enhance the predictive capacity for rainfall-induced debris flows and provide practical criteria for hazard assessment in post-glacial volcanic terrains.

Climate change has increased extreme rainfall events in the Central Southern Andes, favouring slope instabilities and triggering landslides. However, other predisposing factors that control landslides in this region are still poorly constrained. We systematically study the link between landslides and active faults systems thought detailed mapping and classification, highligthing mainly rock avalanches. Our analysis was complemented with hand-specimen and optical microscope host rock description, clay classification via x-ray diffraction and fluorescence, and an exhaustive fault kinematics assessment to determine the controlling the strain in the zone. Our results show that 90.5% of the landslides are linked with active strike-slip faults, characterised by phyllosilicate-bearing hydrothermally altered host rock. In this regard, the presence of clay minerals in fault-slip planes contributes to the generation of landslides in mountain ranges. This phenomenon could be enhanced due the ability to clays induce pressure variations by swelling triggering by extreme rainfalls. This interaction between faults and landslides is important for geological hazard assessment and landslide monitoring as being a recurrent configuration in this section of the Central Southern Chilean 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.

Llaima Volcano (38.692 degrees S, 71.729 degrees W) is one of the most active centers in South America, with-56 eruptions since 1852 CE. During the last eruptive cycle (2007-2009), the volcano displayed typical features of open conduit systems, with frequent long-period volcanic seismicity (LP). After the MW 8.8 Maule megathrust earthquake (27 February 2010), Llaima volcano located 305 km to SE of the epicenter, has experienced one of the longest periods of quiescence since 1852, with reduced activity observed since the beginning of its continuous instrumental monitoring in the year 2007. To better understand this behavior, we track the repose time between eruptions in the 20th century to depict the current period of quiescence and provide details of the pattern of volcano seismicity after the earthquake. The number of LP events decreased-90% shortly after the earthquake. In turn, crustal faults nearby (-20 km south of the main crater) showed an increased level of seismicity lasting for approximately six months after the mainshock before returning to background levels. In order to propose driving mechanisms for such behavior, we computed the static changes of the stress tensor on chosen receiver structures. The acting receiver structure differs from those related to the long-term stress regime controlled by regional tectonics and was inferred from the pre-earthquake shallow seismicity (2007-2009). LP and volcanotectonic seismicity (VT) before the earthquake were located in a NW-SE pattern, in contrast to the NE-trending alignment of flank vents (and hence dike swarms) usually interpreted as an indicator of the maximum horizontal stress axis. From the static stress transfer imparted by the earthquake, we find that an opening event would have occurred at a NW-trending receiver structure coupled with closing of other potential structures, which promoted magma storage along this blind structure but precluding further propagation to the surface. Our results thus show a rare example of earthquake-induced suppression of volcanic activity, where the geometry of the fault-fracture network that shape the plumbing system likely plays a major role.

High-silica explosive eruptions are one of the most dangerous natural phenomena, yet it is unclear which processes are involved in this infrequent kind of event. We present the first systematic characterization of near-field seismicity associated with a large high-silica eruption analyzing data recorded before, during and after the 4 June 2011 rhyolitic eruption of Puyehue–Cordón Caulle Volcanic Complex (PCCVC). Results of a first-level data processing, developed by the Southern Andean Volcano Observatory (OVDAS) to monitor unrest and the evolution of the eruption, are complemented here with the relocation of hypocenters into a local 1D velocity model, the time series of the b value and the computation of the focal mechanism. This information allows us to define several phases before and after the onset of the eruption, describing details of the space–time evolution of seismicity, defining and characterizing the seismic sources, and identifying the structural control of the magmatic intrusion and stress variations during the eruption. Our results illuminate several underlying processes, with emphasis on the possible role that basement structures had on the storage, transport and evacuation of magma. Integrating our results with previous findings based on satellite geodesy and petrology of erupted materials, we discuss general conceptual models regarding destabilization of structurally controlled acidic magmatic systems, the pass from unrest to eruption, and changes in eruptive style and waning phases of eruptions, with broader implications for monitoring and forecast of violent silicic eruptions.

Here we present a number of figures and tables that compliment part of the results discussed in the main text. Figure S1. Typical waveform of HB events before the eruption.This example is for a HB event registered by POC station on April 27 th , 2011, with an ML:4.7.The amplitude is measurement in micrometers/second.Mid and lower panels show the spectra in seismic power and finally the spectrogram in Hz.This event was recorded throughout the Chilean National Volcanic Monitoring Network (RNVV in Spanish) from Lascar volcano, located 1950 km to the north, to Hudson volcano, 610 km to the south distant of the PCCVC.

The 2015M(W)8.3 Illapel earthquake was followed in a time frame of weeks to months by very different responses from Nevados de Chillan, Copahue, and Villarrica volcanoes, all located more than 580 km from the rupture zone. Here we show how Nevados de Chillan and Copahue started new eruptive phases, and Villarrica entered in a period of relative calm. Using seismic, geodetic, and geochemical observations, in combination with numerical wave propagation simulations, we also show that the geometry of the fault system controlled the impact of the earthquake on each volcano. We argue that the sensitivity of a volcano toward an earthquake depends on both its critical state before the mainshock and the geometry of its fault system. This is a case where the same earthquake generates very different responses at the same time, at large distances, rendering volcanoes as very sensitive systems.

Llaima 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 (VEl3) 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 and >2000 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. (C) 2019 Elsevier B.V. All rights reserved.

Correlations between SO2 flux, seismicity, and outgassing activity at the open vent of Villarrica volcano, Chile Journal Item How to cite: Palma, José Luis; Calder, Eliza S.; Basualto, Daniel; Blake, Stephen and Rothery, David A. (2008). Correlations between SO2 flux, seismicity, and outgassing activity at the open vent of Villarrica volcano, Chile. Journal of Geophysical Research: Solid Earth, 113(B10) B10201.

The Puyehue-Cordon Caulle Volcanic Complex (PCCVC) is one of the best examples of tectonic control on volcanism at the Southern Volcanic Zone of the Andes (southern Chile). The PCCVC comprises several volcanic centres that erupted dominantly SiO2-rich magmas at the intersection of the trench-parallel Liquine-Ofqui Fault Zone (LOFZ) and an inherited NW-SE basement structure. The PCCVC began an explosive and later effusive eruption on 2011 June 4 causing decimetre-to metre-scale surface deformation that was observed by a series of Envisat ASAR satellite scenes. We modelled this data and complemented it with timeseries of two continuous GPS stations and seismicity recorded by a local network. Deformation during the first 3 days of the eruption can be modelled either by two point sources aligned with the NW-SE Cordon Caulle graben or by a closing dyke with a significant component of left-lateral motion along the graben. These models are discussed with respect to their implications on the estimated rheology and the eruption mechanism. GPS observations near the volcanic complex reveal an additional, more localised effect related to the LOFZ in the south of the complex. Coeruptive deformation at the main geological structures of the PCCVC is further supported by relocated seismicity, which is concentrated along the Cordon Caulle graben and to the western side of the LOFZ.

The Open University's repository of research publications and other research outputs Correlations between SO2 flux, seismicity, and outgassing activity at the open vent of Villarrica volcano, Chile Journal Article

Cordon Caulle is a large fissural volcano that has erupted rhyodacitic magma of the same composition in its past three historical eruptions in 1921, 1960, and 2011-2012. There was significant ground deformation observed before and during the 2011-2012 eruption-here we use C and X band interferometric synthetic aperture radar (InSAR) time series results to document posteruptive uplift up to 0.8m between March 2012 and May 2015, with line-of-sight rates up to 45 cm/yr that have been largely aseismic, along with subsidence in the 2011-2012 lava flow. The 2012 uplift rate is one of the largest for silicic systems and was likely produced by the intrusion of similar to 0.125 km(3) of magma in the same tectonically controlled plumbing system that has been active during the historical eruptions. Nevertheless, the uplift ended before the reservoir refilled with the erupted volume, maybe due to a change in the pressure gradient produced by the 2011-2012 eruption.