Long-term probabilistic volcanic hazard assessment using open and non-open data: observations and current issues

Probabilistic volcanic hazard assessment (PVHA) has become the paradigm to quantify volcanic hazard over the last decades. Substantial aleatory and epistemic uncertainties in PVHA arise from complexity of physico-chemical processes, impossibility of their direct observation and, importantly, a severe scarcity of observables from past eruptions. One factor responsible for data scarcity is the infrequency of moderate/large eruptions; other factors include lack of discoverability and accessibility to volcanological data. Open-access databases can help alleviate data scarcity and have significantly contributed to long-term PVHA of eruption onset and size, while are less common for data required in other PVHA components (e.g., vent opening). Making datasets open is complicated by economical, technological, ethical and/or policy-related challenges. International synergies (e.g., Global Volcanism Program, WOVOdat, Global Volcano Model, EPOS) will be key to facilitate the creation and maintenance of open-access databases that support Next-Generation PVHA. Additionally, clarification of some misconceptions about PVHA can also help progress. Firstly, PVHA should be understood as an expansion of deterministic, scenario-based hazard assessments. Secondly, a successful PVHA should sometimes be evaluated by its ability to deliver useful and usable hazard-related messages that help mitigate volcanic risk. Thirdly, PVHA is not simply an end product but a driver for research: identifying the most relevant sources of epistemic uncertainty can guide future efforts to reduce the overall uncertainty. Broadening of the volcanological community expertise to statistics or engineering has already brought major breakthroughs in long-term PVHA. A vital next step is developing and maintaining more open-access datasets that support PVHA worldwide

Modeling Uncertainty in Volcanic Hazards with Focus on Pyroclastic Density Currents from Neapolitan Volcanoes

Pyroclastic Density Currents (PDCs) are fast-moving hot mixtures of volcanic gas and particles that can devastate significant areas surrounding explosive volcanoes. Moreover, volcanoes are typically multi-hazard environments where secondary processes, like volcaniclastic mudflows (lahars), can be equally or more dangerous than PDCs. In this view, quantitative volcanic (multi) hazard assessment is among the most pursued goals of modern volcanology. However, the assessment is affected by deep variability-related (aleatory) and knowledge-related (epistemic) uncertainties. De facto, hazard analyses of PDCs and lahars quantifying such uncertainties are uncommon because modeling their complex flow dynamics, in a stochastic scheme, has a high computational cost. In this PhD, different probabilistic approaches to model and quantify uncertainty in volcanic hazard assessment are explored and implemented at two Italian volcanoes: Somma-Vesuvius and Campi Flegrei. First, it is demonstrated that simple PDC models (Energy Cone), coupled with Monte Carlo sampling, are able to: (1) reproduce the spatial extent of past PDC deposits, and (2) quantify epistemic uncertainty comprehensively. Secondly, by merging Energy Cone simulations with more complex statistical models (Bayesian Event Tree for Volcanic Hazard, BET_VH), a cutting-edge hazard product is computed: a multi-volcano, single-target probabilistic PDC hazard assessment over the central Campania region. Thirdly, through assembling more sophisticated PDC models (Titan2D) with Polynomial Chaos Quadrature and BET_VH, hazard curves for dense pumice flows from Somma-Vesuvius are obtained. These curves are extremely valuable for quantitative volcanic risk analyses. Finally, probabilistic volcanic multi-hazard assessment is performed at Somma-Vesuvius by combining a Bayesian Belief Network (Multihaz: which incorporates probabilistic hazard analyses of tephra fallout and dense PDCs and models aleatory uncertainty in lahar triggering) and a numerical model of lahars (LaharFlow: which allows to compute probabilistic hazard footprints). Future steps in probabilistic volcanic hazard assessment will likely require strategies that are multi-disciplinary and explicitly oriented to calculate volcanic hazard

VOLCANS: an objective, structured and reproducible method for identifying sets of analogue volcanoes

The definition of a suite of analogue volcanoes, or volcanoes that are considered to share enough characteristics as to be considered exchangeable to a certain extent, is becoming a key component of volcanic hazard assessment. This is particularly the case for volcanoes where data are lacking or scarce. Moreover, volcano comparisons have often been based on similarities and differences inferred through expert judgement and not necessarily informed by volcano characteristics from global datasets. These similarities can be based on a range of features, from very simplified (e.g. statrovolcanoes) to very specific (e.g. detailed eruption chronologies), and may be strongly influenced by the personal experience of individuals or teams conducting the analogue analysis. In this work, we present VOLCANS (VOLCano ANalogues Search)—an objective, structured and reproducible method to identify sets of analogue volcanoes from global volcanological databases. Five overarching criteria (tectonic setting, rock geochemistry, volcano morphology, eruption size and eruption style), and a structured combination of them, are used to quantify overall multi-criteria volcano analogy. This innovative method is complementary to expert-derived sets of analogue volcanoes and provides the user with full flexibility to weigh the criteria and identify analogue volcanoes applicable to varied purposes. Some results are illustrated for three volcanoes with diverse features and significant recent and/or ongoing eruptions: Kı̄lauea (USA), Fuego (Guatemala) and Sinabung (Indonesia). The identified analogue volcanoes correspond well with a priori analogue volcanoes derived from expert knowledge. In some cases, single-criterion searches may not be able to isolate a reduced set of analogue volcanoes but any multi-criteria search can provide high degrees of granularity in the sets of analogue volcanoes obtained. Data quality and quantity can be important factors, especially for single-criterion searches and volcanoes with very scarce data (e.g. Sinabung). Nevertheless, the method gives stable results overall across multi-criteria searches of analogue volcanoes. Potential uses of VOLCANS range from quantitative volcanic hazard assessment to promoting fundamental understanding of volcanic processes

Probabilistic volcanic hazard assessment for pyroclastic density currents from pumice cone eruptions at Aluto Volcano, Ethiopia

Aluto volcano, in the Main Ethiopian Rift, is a peralkaline caldera system, which comprises conglomerations of rhyolite (obsidian) lavas and enigmatic pumice cones. Recent work at Aluto has found that pumice cone eruptions are highly unsteady, and form convective eruption plumes that frequently collapse to generate pyroclastic density currents (PDCs). We develop a methodology and present results for the first probabilistic volcanic hazard assessment (PVHA) for PDCs at a pumice cone volcano. By doing so, we estimate the conditional probability of inundation by PDCs around Aluto volcano, incorporating the aleatory uncertainty in PDC hazard. We employ a Monte Carlo energy cone modeling approach, which benefits from parameterization informed by field investigations and volcanic plume modeling. We find that despite the relatively modest eruptions that are likely to occur, the wide distribution of past vent locations (and thus the high uncertainty of where future vents might open), results in a broad area being potentially at risk of inundation by PDCs. However, the aleatory uncertainty in vent opening means that the conditional probabilities are lower (≤ 0.12), and more homogeneous, over the hazard domain compared to central-vent volcanoes (where conditional probabilities are often ≤ 1 close to the vent). Despite this, numerous settlements, amenities, and economically valuable geothermal infrastructure, lie within the most hazardous (P(PDC|eruption) ≥ 0.05) regions of Aluto caldera. The Monte Carlo energy cone modeling approach provides a quantitative, accountable and defendable background and long-term PVHA for PDCs from Aluto. These results could be combined in the future with hazard assessments relating to tephra fall and/or lava to develop a comprehensive volcanic hazard map for the caldera. Following appropriate parameterization, the approach developed here can also be used to compute a PDC PVHA at other volcanoes where vent location is uncertain

Probabilistic hazard from pyroclastic density currents in the Neapolitan Area (Southern Italy)

The metropolitan area of Napoli (∼3 M inhabitants) in southern Italy is located in between two explosive active volcanoes: Somma‐Vesuvius and Campi Flegrei. Pyroclastic density currents (PDCs) from these volcanoes may reach the city center, as witnessed by the Late Quaternary stratigraphic record. Here we compute a novel multivolcano Probabilistic Volcanic Hazard Assessment of PDCs, in the next 50 years, by combining the probability of PDC invasion from each volcano (assuming that they erupt independently) over the city of Napoli and its surroundings. We model PDC invasion with the energy cone model accounting for flows of very different (but realistic) mobility and use the Bayesian Event Tree for Volcanic Hazard to incorporate other volcano‐specific information such as the probability of eruption or the spatial variability in vent opening probability. Worthy of note, the method provides a complete description of Probabilistic Volcanic Hazard Assessment, that is, it yields percentile maps displaying the epistemic uncertainty associated with our best (aleatory) hazard estimation. Since the probability density functions of the model parameters of the energy cone are unknown, we propose an ensemble of different hazard assessments based on different assumptions on such probability density functions. The ensemble merges two plausible distributions for the collapse height, reflecting a source of epistemic (specifically, parametric) uncertainty. We also apply a novel quantification for a spatially varying epistemic uncertainty associated to PDC simulations

A simple two-state model interprets temporal modulations in eruptive activity and enhances multivolcano hazard quantification

Volcanic activity typically switches between high-activity states with many eruptions and low-activity states with few or no eruptions. We present a simple two-regime physics-informed statistical model that allows interpreting temporal modulations in eruptive activity. The model enhances comprehension and comparison of different volcanic systems and enables homogeneous integration into multivolcano hazard assessments that account for potential changes in volcanic regimes. The model satisfactorily fits the eruptive history of the three active volcanoes in the Neapolitan area, Italy (Mt. Vesuvius, Campi Flegrei, and Ischia) which encompass a wide range of volcanic behaviors. We find that these volcanoes have appreciably different processes for triggering and ending high-activity periods connected to different dominant volcanic processes controlling their eruptive activity, with different characteristic times and activity rates (expressed as number of eruptions per time interval). Presently, all three volcanoes are judged to be in a low-activity state, with decreasing probability of eruptions for Mt. Vesuvius, Ischia, and Campi Flegrei, respectively

Megacristales de kaersutita en los diques máficos alcalinos del plutón de Panticosa (Zona Axial Pirenaica): xenocristales de origen profundo

Megacrysts of kaersutite have been identified in several alkaline mafic dikes from the Panticosa pluton. They show strongly anhedral habits and resorption features, including Krs overgrowths and/or Cpx-Opq coronae. Chemically, the liquid in equilibrium with the megacryst cores is clearly different from the host alkaline dikes. In contrast, the liquid in equilibrium with Krs overgrowths and Cpx from the coronae agrees with the composition of some of the host alkaline dikes. According to the obtained results, Krs megacrysts must be considered xenocrysts. Therefore, their Middle Permian age (268 Ma) predates the emplacement of the alkaline dikes. The xenocrysts crystallised at about 30 km depth and were afterwards reequilibrated at lower depthsEn los diques máficos alcalinos del plutón de Panticosa se han identificado megacristales de kaersutita.Muestran hábitos anhedrales y características típicas de reabsorción, así como recrecimientos de Krs y de una corona de Cpx y Opq. Los fundidos en equilibrio con los núcleos de Krs son muy distintos de los diques alcalinos que los contienen, mientras que los fundidos en equilibrio con los recrecimientos de Krs y los Cpx de las coronas son similares a algunos de los diques. Por lo tanto, los megacristales de Krs son xenocristales y su edad, Pérmico Medio (268 Ma), es previa a la edad de emplazamiento de los diques. Los xenocristales se formaron a unos 30 km de profundidad y se reequilibraron a menor profundida

The lamprophyre dikes in the Panticosa Pluton (Pyrenean Axial Zone): syn-emplacement with later-hercynian extension

El Plutón de Panticosa muestra dos grupos de diques de lamprófido con afinidades calcoalcalina y alcalina, emplazados en el intervalo Pérmico inferior y medio. Para estos diques, no se observa una clara relación entre sus orientaciones, dimensiones y composición. El análisis cinemático de los diques permite obtener una dirección de extensión próxima a N-S, compatible con la orientación del vector desplazamiento medido en campo. Los datos estructurales relacionados con la geometría de los diques y su cinemática y el patrón de fracturación del granito encajante permite proponer un modelo de emplazamiento para ambos litotipos dentro de un contexto extensional. Este modelo contempla tanto el emplazamiento del magma calcoalcalino (Pérmico inferior) asociado a fusión cortical, como el del magma alcalino (Pérmico medio), de carácter astenosférico. Este régimen extensional es posterior al régimen transpresivo de edad Carbonífero superior responsable del emplazamiento y fracturación del plutón graníticoThe Panticosa Pluton shows two groups of lamprophyre dykes with calcalkaline and alkaline affinities, which are emplaced during the Lower-Middle Permian interval. A clear relationship between their orientations, dimensions and composition does not occur. The kinematic analysis of the dykes gives a near N-S extension direction compatible with the orientation of the displacement vector measured in the field. The structural data related to the dyke geometry and kinematics and the fracturing pattern of the granitic pluton allow to propose an emplacement model for both lithotypes within a common extensional framework; this model includes both the former Lower Permian calc-alkaline magma, affected by crustal contamination and the Middle Permian mantle alkaline magma. This extensional regime post-dates the Upper Carboniferous transpressive regime responsible for the emplacement and fracturing of the granitic pluto