Pablo Samaniego’s research while affiliated with French National Centre for Scientific Research and other places
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Volcanic systems behave episodically and require mechanisms for magma segregation, instability and ascent. Here, we discuss the processes that promote the ascent of magma to the Earth's surface and prepare the onset of an eruption, thus acting as triggers, as well as the factors that prevent eruption. We describe the various petrological, geochemical and geophysical observations that reveal the triggering processes and events. Based on emerging concepts of magma plumbing systems, we consider the mechanisms involved, the buoyancy and overpressure of magmas and associated fluids, using modelling approaches. The transient increase in magma inflow at depth, leading to magma recharge at shallow levels, and the increase in volatile content during ascent are key ingredients of internal triggering. Events, such as earthquakes, changes in surface loading and interactions with external water and hydrothermal systems, perturb the stress field, change magma and fluid pressures to act as external triggers.
Sangay volcano (Ecuador) shows a quasi-continuous activity at least since the seventeenth century and has produced several eruptions which affected towns and cities at considerable distance (up to > 170 km). For this reason, despite its remote location, recent efforts were aimed at reviewing its volcanic history, quantifying the occurrence probability of four eruptive scenarios of different magnitude (Strong Ash Venting, Violent Strombolian, sub-Plinian, and Plinian) and the associated uncertainty, and, for each eruptive scenario, estimating the probability distribution of key eruptive source parameters (fallout volume, average plume height, and eruption duration). In this study, we utilize such information to produce probabilistic hazard maps and curves. To this aim, we use coupled plume and dispersal models (PLUME-MOM-TSM and HYSPLIT, respectively) with the application of a novel workflow for running an ensemble of thousands of simulations following a sto-chastic sampling of input parameters. We produced probabilistic hazard maps for each scenario by considering four ground load thresholds (i.e., 0.1, 1, 10, and 100 kg/m 2) and two types of model initialization strategies, based on the elicited total deposit volume and on the elicited plume height, respectively, which produced non-negligible differences. In addition, we produced hazard curves for nine sites of interest from a risk perspective, corresponding to towns/cities potentially affected by tephra accumulation. Finally, we also derived combined maps by merging maps of single scenarios with their probability of occurrence as obtained from expert elicitation. Results indicate that in case of a future eruption, even for a moderate-scale one (Violent Strombolian), probability of tephra accumulation larger than 1 kg/m 2 is relatively high (from 21 to 24% considering different model initializations) in the town of Guamote, i.e., the most severely affected site among those tested (43 km W of Sangay). For larger-scale events (i.e., sub-Plinian), the impact of tephra accumulation results to be significant even for the city of Guayaquil (176 km W of Sangay), with probability of tephra accumulation larger than 1 kg/m 2 from 3 to 22% considering different model initializations. For maps combining single maps of historically observed scenarios, the probability (%-[5 th-Mean-95 th ]) of having ≥ 10 kg/m 2 for Guamote is [4-13-25] as maximum values.
Magma storage modulates the explosivity, frequency, and impact of volcanic eruptions, and controls the formation of magmatic-hydrothermal mineral deposits. The architecture of magma storage and plumbing systems, and their eruption triggering mechanisms, are inaccessible to direct observation in active volcanoes. However, they can be accessed through the study of products of volcanic eruptions: volcanic rocks and the crystal, melt, and gas records they contain. This chapter explores the texture and composition of volcanic rocks (and their plutonic cargoes) to better understand pre-eruptive magma storage and transfer from storage to eruption. We take a rock-centred approach to understanding magma-mush storage systems feeding volcanism, discussing traditional as well as new approaches, and their implications for volcano monitoring efforts.
We assess the volcanic hazard posed by pyroclastic density currents (PDCs) at Tungurahua volcano, Ecuador, using a probabilistic approach based on the analysis of calibrated numerical simulations. We address the expected variability of explosive eruptions at Tungurahua volcano by adopting a scenario-based strategy, where we consider three cases: violent Strombolian to Vulcanian eruption (VEI 2), sub-Plinian eruption (VEI 3), and sub-Plinian to Plinian eruption (VEI 4–5). PDCs are modeled using the branching energy cone model and the branching box model, considering reproducible calibration procedures based on the geological record of Tungurahua volcano. The use of different calibration procedures and reference PDC deposits allows us to define uncertainty ranges for the inundation probability of each scenario. Numerical results indicate that PDCs at Tungurahua volcano propagate preferentially toward W and NW, where a series of catchment ravines can be recognized. Two additional valleys of channelization are observed in the N and NE flanks of the volcano, which may affect the city of Baños. The mean inundation probability calculated for Baños is small (6 ± 3%) for PDCs similar to those emplaced during recent VEI 2 eruptions (July 2006, February 2008, May 2010, July 2013, February 2014, and February 2016), and on the order of 13 ± 4% for a PDC similar to that produced during the sub-Plinian phase of the August 2006 eruption (VEI 3). The highest intensity scenario (VEI 4–5), for which we present and implement a novel calibration procedure based on a few control points, produces inundation areas that nearly always include inhabited centers such as Baños, Puela, and Cotaló, among others. This calibration method is well suited for eruptive scenarios that lack detailed field information, and could be replicated for poorly known active volcanoes around the world.
We present a tephra fallout hazard assessment of Sangay volcano, Ecuador. This volcano is under semi-permanent activity at least since the 17th century, and has produced several eruptions whose products have affected towns and cities at considerable distance (up to > 170 km). For this reason, despite its remote location, recent efforts have been aimed at reviewing its volcanic history; quantifying the occurrence probability of various eruptive scenarios and the associated uncertainty; and, for each eruptive scenario, estimating the probability distribution of key eruptive source parameters (fallout volume, average plume height and eruption duration). In this study, we use this information to produce probabilistic hazard maps by using the coupled models PLUME-MOM-TSM and HYSPLIT, with the application of a novel workflow for running an ensemble of thousands of simulations following a stochastic sampling of input parameters. Probabilistic hazard maps have been produced for four scenarios of different magnitudes. For each scenario, we considered four ground load thresholds (0.1, 1, 10 and 100 kg/m ² ) and two types of model initialization strategies (based on the elicited total deposit volume and on the elicited plume height respectively), which produced non-negligible differences. Hazard curves have also been produced for nine sites of interest from a risk perspective, corresponding to towns/cities potentially affected by tephra accumulation. Combined maps have also been produced by merging maps of single scenarios with their probability of occurrence. Results indicate that in case of a future eruption, even for a moderate-scale eruption (Violent Strombolian), probability of tephra accumulation larger than 1 kg/m ² is relatively high (up to 20–25%) in the town of Guamote, i.e. the most severely affected site among those tested (43 km W of Sangay). For larger-scale events (Sub Plinian) the impact of tephra accumulation could be significant even for the city of Guayaquil (176 km W of Sangay), with probability of tephra accumulation larger than 1 kg/m ² up to 22%.
Sangay volcano is considered as one of the most active volcanoes worldwide. Nevertheless, due to its remote location and low-impact eruptions, its eruptive history and hazard scenarios are poorly constrained. In this work, we address this issue by combining an analysis of monitoring data and historical chronicles with expert elicitation. During the last 400 years, we recognize periods of quiescence, weak, and enhanced eruptive activity, lasting from several months to several years, punctuated by eruptive pulses, lasting from a few hours to a few days. Sangay volcano has been mainly active since the seventeenth century, with weak eruptive activity as the most common regime, although there have also been several periods of quiescence. During this period, eruptive pulses with VEI 1–3 occurred mainly during enhanced eruptive activity and produced far-reaching impacts due to ash fallout to the west and long-runout lahars to the south-east. Four eruptive pulse scenarios are considered in the expert elicitation: strong ash venting (SAV, VEI 1–2), violent Strombolian (VS, VEI 2–3), sub-Plinian (SPL, VEI 3–4), and Plinian (PL, VEI 4–5). SAV is identified as the most likely scenario, while PL has the smallest probability of occurrence. The elicitation results show high uncertainty about the probability of occurrence of VS and SPL. Large uncertainties are also observed for eruption duration and bulk fallout volume for all eruptive scenarios, while average column height is better characterized, particularly for SAV and VS. We interpret these results as a consequence of the lack of volcano-physical data, which could be reduced with further field studies. This study shows how historical reconstruction and expert elicitation can help to develop hazard scenarios with uncertainty assessment for poorly known volcanoes, representing a first step towards the elaboration of appropriate hazard maps and subsequent planning.
The Ecuadorian arc is composed of an unusually high number of volcanoes organized as along-arc alignments and across-arc clusters, over a relatively small area. Although several geochronological studies were carried out in the past three decades, the eruptive history of the central zone of the arc remained poorly documented, preventing the analyses of volcanism initiation of the whole arc. In this study, we present new K-Ar ages obtained from this central area, referred as the Quito segment. These results were then included in an updated comprehensive geochronological database including about 250 ages, allowing us to describe, at the arc scale, the spatial and temporal development of Quaternary volcanic activity in Ecuador. About eighty Quaternary volcanoes are identified in the Ecuadorian Andes, amounting to 45 volcanic complexes with radiometric ages and/or identified as active or potentially active. The volcanic arc developed in three stages marked by increases in the total number of active volcanoes. During the oldest Plio-Early Pleistocene stage, the documented volcanic activity was mostly concentrated in the Eastern Cordillera of the Quito segment, with minor effusive eruptions in the southern Back-Arc. Since ~ 1.4 Ma, the activity spread to the surroundings of the Quito segment and new edifices also appeared in the Western Cordillera and the Inter-Andean Valley. Towards the end of this intermediate stage (i.e., ~ 800 ka), volcanism occurred in isolated areas to the north and south of the Inter-Andean Valley. Finally, the late and current stage was characterized by a remarkable increase in volcanic activity since ~ 600 ka. Approximately 50 volcanoes were active during this stage. The spatial distribution of the Ecuadorian arc volcanism seems to be guided by deep mechanisms and old crustal tectonic structures from the Western Cordillera, whereas the neotectonics seem to influence the development of stratovolcanoes. In addition, we note that the spatial and temporal evolution of volcanism highlights the influence of the Carnegie Ridge and the thermal regime anomaly of the young Nazca crust on the increase of volcanic activity in Ecuador.
We assess the volcanic hazard derived from pyroclastic density currents (PDCs) at Tungurahua volcano, Ecuador, using a probabilistic approach based on the analysis of calibrated numerical simulations. We address the expected variability of explosive eruptions at Tungurahua volcano by adopting a scenario-based strategy, where we consider three cases: small magnitude violent Strombolian to Vulcanian eruption (VEI 2), intermediate magnitude sub-Plinian eruption (VEI 3), and large magnitude sub-Plinian to Plinian eruption (VEI 4–5). PDCs are modeled using the branching energy cone model and the branching box model, considering reproducible calibration procedures based on the geological record of Tungurahua volcano. The use of different calibration procedures and reference PDC deposits allows us to define uncertainty ranges for the inundation probability of each scenario. Numerical results indicate that PDCs at Tungurahua volcano propagate preferentially toward W and NW, where a series of catchment ravines can be recognized. Two additional valleys of channelization are observed in the N and NE flanks of the volcano, which may affect the city of Baños. The mean inundation probability calculated for Baños is small (6 ± 3%) for PDCs similar to those emplaced during the VEI 2 eruptions of July 2006, February 2008, May 2010, July 2013, February 2014 and February 2016, and on the order of 13 ± 4% for a PDC similar to that produced during the sub-Plinian phase of the August 2006 eruption (VEI 3). The highest energy scenario (VEI 4–5), for which we present and implement a novel calibration procedure based on a few control points, produces inundation areas that nearly always include inhabited centers such as Baños, Puela and Cotaló, among others. This calibration method is well suited for eruptive scenarios that lack detailed field information, and could be replicated for poorly-known active volcanoes around the world.
... Furthermore, large populations of samples can then be passed as inputs to Monte Carlo simulations which propagate the related uncertainties across the components of the physical or probabilistic models, e.g., to characterize stochastic eruption parameters or to compute hazard levels, respectively (e.g. Bevilacqua et al. 2017;2022a;Tadini et al. 2025a;Pardini et al. 2025). ...
... For comparative purposes, Target Item distributions were also computed with Equal Weights (EW) applied to all participating experts (e.g. Neri et al. 2008;Tadini et al. 2017;Bernard et al. 2024). ELICIPY outputs were checked for consistency and successfully validated with other, widely adopted, software for structured expert judgment elicitation analysis, e.g., EXCALIBUR and ANDURIL/ANDURYL (Rongen et al. 2020 and references therein). ...
... Natural disasters like volcanic eruptions or rising temperatures can affect biodiversity and, consequently, the flow of tourists, impacting the local economy. For instance, climate phenomena like El Niño impact the conservation of endemic species (Valle et al. 1987), and Sierra Negra's eruption in 2005 and 2018 led to the disruption of tourist activities and commerce (Hidalgo et al. 2024). Regarding regulating services, these include maintaining air quality and mitigating extreme events, such as storms and tsunamis, which affect both island infrastructure and the protection of fragile ecosystems (Thrush and Dayton 2010). ...
... This event was a paroxysmal phase of an eruptive period that started in 1999 and finished in 2016, during which volcanic activity occurred sporadically, including Strombolian, violent Strombolian, and Vulcanian events (Anderson et al. 2018;Bernard 2018;Battaglia et al. 2019;Palacios et al. 2023;Parra et al. 2016). Among the products emitted during this period, it is possible to recognize PDC deposits of a series of events that occurred in July 2006, February 2008, May 2010, July 2013, February 2014, and February 2016Hall et al. 2015;Gaunt et al. 2020;Falasconi et al. 2023), whose deposits are here used to calibrate our numerical simulations. ...
... We used a database of chemical analyses from the AVC (Samaniego et al., 2016) that has just been augmented by Rivera et al. (2023). Four rock samples were analyzed to determine the chemical composition of Fig. 7. 40 Ar/ 39 Ar plateau and isochron ages of the selected samples from Hualca Hualca volcano. ...
... It is a goal we are still chasing today. The substantial evidence for post-fragmentational deformation of pyroclastic particles from the minor deformation exhibited by breadcrust bombs (Colombier et al., 2023a) to the wholesale welding a rheomorphic transformation of glassy lava both in the conduit (Tuffen et al., 2003;Tuffen and Dingwell, 2005), and on the Earth´s surface, together with the additional complexity of transport-driven shape relaxation of particles, and post-fragmentation ash-gas reactions (Ayris et al., 2014;Casas et al., 2019) and winnowing have added to the challenge. Obtaining the full picture of the journey from pre-eruptive, bubbly volcanic magma to dispersed volcanic products from the Earth´s surface to its stratosphere employs a great deal of research capacity to this day. ...
... On the southernmost edge of the DMQ is situated the 0.45 Ma old extinct Pasochoa volcano (GS18), which hosts one of the last remnants of a cloud forest in the Interandean Valley [131,132]. The Pasochoa volcano is aligned with the Ilalo volcano to its north and the Rumiñahui volcano to its south, having similar geochemical compositions and structures [133,134]. Therefore, its eroded western flank is collapsed, forming a horseshoeshaped amphitheater. The volcano is part of the Pasochoa Wildlife Refuge and a protected forest [135,136] (Figure 5A). ...
... After this activity, the volcano entered a brief pause until about 3100 years ago, when it experienced one of the most explosive events to have occurred in the Ecuadorian volcanic arc during the Holocene. It generated major pyroclastic flows and ash falls, with an estimated volume of at least 5 km 3 [35]. Table 1 shows the chemical composition of the VA, which is mainly composed of silica (SiO 2 ) and alumina (Al 2 O 3 ). ...
... Tungurahua volcano (1.47° S; 78.44° W), located ~ 8 km south of the city of Baños, is one of the most hazardous volcanoes in Ecuador and South America (Fig. 1). The eruption record of Tungurahua includes both effusive and explosive activity, with a series of events documented in historical times, such as those of 1640-1645, 1773-1782, 1885-1888, and 1916-1925(Hall et al. 1999Le Pennec et al. 2016) and, more recently, an eruptive episode that lasted since 1999 until 2016 Samaniego et al. 2011;Vlastélic et al. 2023). In addition, during the Late Holocene, Tungurahua experienced Plinian eruptions and sector collapses (Le Pennec et al. , 2013Bablon et al. 2018), which demonstrate the potential of Tungurahua volcano to feed long-runout distance pyroclastic density currents (PDCs), posing a permanent Editorial responsibility: Editorial responsibility: S. Massaro threat to the surrounding communities such as the city of Baños and other villages in the Tungurahua and Chimborazo Provinces (Fig. 1). ...
... This leads to that the released aqueous fluids are characterized by low F/Cl ratios (0.11±0.09-0.43 ±0.07; Straub and Layne, 2003;Le Voyer et al., 2010;Kendrick et al., 2020;Narváez et al., 2023), causing the magma source region enriched in Cl but much less F. This process, combined with the fact that Cl is more incompatible than F during partial melting , would result in magmas with chemical traits similar to arc magmas with higher Cl contents than F (i.e., F/Cl<1; Figure 6). Similarly, the high Cl concentrations in altered oceanic lithosphere (Kendrick and Barnes, 2022), along with the effective loss of Cl during subduction (Fabbrizio et al., 2013), would result in the Cl/K ratios in arc magmas commonly exceeding those of the PM (Figure 7b). ...
![Figure 2. Conceptual models for magma-mush storage systems across tectonic settings. Growing evidence from geophysical (chapter 1.4.1) and petrological (this chapter) work suggests magma plumbing systems are commonly dominated by crystal mushes with ephemeral eruptible melt pockets (exaggerated for sketching purposes). Colours represent magma-mush composition (more evolved with increasing SiO2), and typical volcano morphologies are added to each tectonic setting, noting they are not exclusive to the depicted settings. Left: Continuous transcrustal storage [1] requires strong heat flux and may develop at the peak of magmatism in arc systems. More typically, storage may be less continuous even if multi-level. The thick crust in continental arcs promotes prolonged magma storage and evolution relative to oceanic arcs and other settings. Shallow storage enhances cooling and differentiation and may lead to explosive volcanism, including caldera-forming eruptions. Middle: In mid-ocean ridges, the limited magmatic journey from shallow magma generation to eruption limits differentiation, with ocean spreading rates controlling magma supply and melt fraction in the mush [2]. Right: In oceanic islands, depth of storage correlates with eruption frequency, considered a proxy for magma flux. Systems with low magma flux like the Canary Islands or Cape Verde are primarily fed directly by upper mantle reservoirs with limited crustal storage [3], whereas high magma flux systems like Hawaii or Réunion develop a stable reservoir at shallow depth [4].](https://www.researchgate.net/publication/386067996/figure/fig2/AS:11431281292050023@1732354002489/Conceptual-models-for-magma-mush-storage-systems-across-tectonic-settings-Growing_Q320.jpg)
