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Fourmentraux, Céline
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Fourmentraux, Céline
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- PublicationRestrictedThe 1974 flank eruption of Mount Etna: An archetype for deep dike-fed eruptions at basaltic volcanoes and a milestone in Etna's recent history(2009)
; ; ; ; ; ; ;Corsaro, R. A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Métrich, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Allard, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Andronico, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Miraglia, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Fourmentraux, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; ; ; ; ; The 1974 western flank eruption of Mount Etna produced a rare, nearly aphyric and plagioclase-free trachybasalt that could not be derived from the central volcano conduits and was more alkaline and more radiogenic than all previous historical lavas. New results for the petrochemistry and volatile content of its products, combined with contemporaneous seismic and volcanological observations, allow us to reinterpret the origin and significance of this event. We show that the eruption was most likely triggered by deep tectonic fracturing that allowed a dike-like intrusion to propagate in 9 days from 11 km depth up to the surface, bypassing the central conduits. Relatively fast, closed system decompression of the volatile-rich magma initially led to lava fountaining and the rapid growth of two pyroclastic cones (Mounts De Fiore), followed by Strombolian activity and the extrusion of viscous lava flows when gas-melt separation developed in the upper portion of the feeding fracture. The 1974 trachybasalt geochemistry indicates its derivation by mixing 25% of preexisting K-poor magma (best represented by 1763 La Montagnola eruption’s products) and 75% of a new K-rich feeding magma that was gradually invading Mount Etna’s plumbing system and became directly extruded during two violent flank eruptions in 2001–2003. We propose to classify 1974-type so-called ‘‘eccentric’’ eruptions on Etna as deep dike-fed (DDF) eruptions, as opposed to more common central conduit-fed flank eruptions, in order to highlight their actual origin rather than their topographic location. We ultimately discuss the possible precursors of such DDF eruptions.260 39 - PublicationOpen AccessProbabilistic invasion maps of pyroclastic density current hazard by using long-term vent opening mapping and simplified invasion models: application to the Campi Flegrei caldera (Italy)(2013)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ;Campi Flegrei is an example of active and densely populated caldera with a very high volcanic risk associated with the occurrence of Pyroclastic Density Currents (PDCs) produced by explosive events of variable scale and vent location. The mapping of PDC hazard in such caldera setting is particularly challenging due to the complex dynamics of the flow, the large uncertainty of future vent location and the complex topography affecting the flow propagation. Nevertheless, probabilistic mapping of PDC invasion, able to account for the intrinsic uncertainties affecting the system, is needed for hazard assessment. In this study, we show the results of new field work and statistical analysis of past eruptive activity aimed at producing long-term probabilistic maps of vent opening at Campi Flegrei. The field work was focused on the structural and morphological nature of the caldera and particularly on the reconstruction of the location of past eruptive vents as well as of main faults and fissures formed in the last 15 kyrs of activity. One objective of the analysis was to incorporate into the vent opening maps the main uncertainties affecting the system. This was done by adopting appropriate density distributions of the probability of vent opening of the different areas of the caldera and by relying on expert judgement. Then, we used these maps to produce a variety of probabilistic PDC hazard maps of the Campi Flegrei area based on different invasion models and accounting for the uncertainty in vent opening and event size. Invasion models were based on simple correlations derived from field reconstruction of past events, one-dimensional models based on a linear decay of the flow energy (e.g. energy line), and simple energy decay models tuned on transient and 2D numerical simulations of the flow dynamics.55 14 - PublicationOpen AccessMapping long-term vent opening in a caldera setting with uncertainty estimation: application to Campi Flegrei caldera (Italy)(2013)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ;Campi Flegrei is an active volcanic area located in the Campanian Plain, along the Tyrrhenian margin of the southern Apennines (Italy), dominated by the formation of a 12 km large, resurgent caldera. The great majority of the eruptions have been explosive, variable in magnitude and intensity and characterized by the generation of remarkable ash fallout and pyroclastic density currents deposits. In this study we present results of field work and statistical analysis of past eruptive activity aimed at producing long-term probabilistic maps of vent opening at Campi Flegrei. Field work was focused on the structural and morphological nature of the caldera and particularly on the reconstruction of the location of past eruptive vents as well as of main faults and eruptive fissures formed in the last 15 kyr of activity. The statistical analysis performed accounted for the spatial distribution of past vent locations but was flexible enough to incorporate the heterogeneous geological information available, such as the density of faults/fissures or the clue of possible past vents hidden by the more recent activity. One key objective of the analysis was to directly incorporate into the maps the main uncertainties affecting the system. This was done by adopting appropriate density distributions of the probability of vent opening of the different areas of the caldera and by relying on expert judgement. Results allowed to quantify the influence of the different theoretical assumptions and sources of uncertainty on the long-term mapping of vent opening. The distributions obtained represent the starting point for the production of long-term ash fallout and pyroclastic density hazard maps at Campi Flegrei caldera.66 14 - PublicationOpen AccessAssessing pyroclastic density current hazard in caldera settings: the example of Campi Flegrei caldera (Italy)(2013)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ;; ;; ; ;; ; ;Mapping of pyroclastic density currents (PDCs) hazard in caldera settings is particularly challenging due to the large uncertainty on future vent location and eruption scale as well as the complex dynamics of the flow over the irregular caldera topography. Nevertheless, probabilistic mapping of PDC invasion, able to account for the intrinsic uncertainties affecting the system, is needed for hazard assessment, particularly for highly populated regions. Campi Flegrei (CF) is a vivid example of active and densely populated caldera with a very high risk associated with the occurrence of PDCs produced by explosive events. In this presentation we show the results of new field work and mathematical modelling of past eruptive activity aimed at producing long-term probabilistic vent opening and PDC invasion maps at CF. Field work was focused on the structural and morphological features of the caldera and particularly on the reconstruction of the location of past eruptive vents as well as of the distribution of the main faults and fractures formed in the last 15 kyr of activity. One specific objective of the analysis was to incorporate into the vent opening maps the main uncertainties affecting the system by adopting appropriate density distributions and by relying on expert judgement. We then used these maps to produce, by adopting a Monte Carlo approach, a variety of probabilistic PDC hazard maps of the CF area based on different invasion models and accounting for the uncertainty on vent location and event scale. In particular we developed and adopted a simplified invasion flow model based on the so-called box model approximation and tuned on transient and 2D numerical simulations of the flow dynamics. The new model allowed to describe the exponential decay of the flow energy as well as to account for first-order topographic effects. The developed methodology appears able to provide relatively quick and robust probabilistic assessments of PDC hazard in caldera settings and could be potentially extended to other calderas worldwide.65 13 - PublicationOpen AccessMapping long-term pyroclastic density current hazard in a caldera setting: application to Campi Flegrei caldera (Italy)(2012)
; ; ; ; ; ; ; ; ; ; ;; ; ; ;; ; The Campi Flegrei (CF) is an active volcanic area located in the Campanian Plain, along the Tyrrhenian margin of the Southern Appennines (Italy), dominated by the formation of a 12 km large, resurgent caldera. The nested Campi Flegrei caldera results from successive collapses related to the eruptions of the Campanian Ignimbrite (CI; 39.3±0.1 ka) and Neapolitan Yellow Tuffs (NYT; 14.9±0.4 ka). After the NYT eruption, volcanism was concentrated in three epochs of activity, alternating to periods of quiescence. The great majority of the eruptions have been explosive, variable in magnitude and also characterized by the generation of fallout, ash deposits and pyroclastic density currents (PDCs). We present here a methodology aimed at the construction of a probability map of PDC hazard of the CF area. At this stage, results are preliminary and will be improved by future research work. Nevertheless, first outcomes already provide numerous insights in the problem and contribute to define future research directions. In the study we had to cope with three different problems, related to different probability spaces: • constructing a probability map of the place of a new vent opening • giving a probability law to the area of invasion of a PDC from a fixed new vent • choosing a probability distribution for the uncertainty that affects the model itself To calculate the probabilistic simulations we used the R statistics software, and to plot the maps we used the ESRI platform.80 24 - PublicationRestrictedCrystal fractionation, magma step ascent, and syn-eruptive mingling: the Averno 2 eruption (Phlegraean Fields, Italy)(2012-06)
; ; ; ; ;Fourmentraux, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Métrich, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Bertagnini, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Rosi, M.; Dipartimento di Scienze della Terra, Pisa, Italy; ; ; The 3.7 ka year-old Averno 2 eruption is one of the rare eruptions to have occurred in the northwest sector of the Phlegraean Fields caldera (PFc) over the past 5 ka. We focus here on the fallout deposits of the pyroclastic succession emplaced during this eruption. We present major and trace element data on the bulk pumices, along with major and volatile element data on clinopyroxene-hosted melt inclusions, in order to assess the conditions of storage, ascent, and eruption of the feeding trachytic magma. Crystal fractionation accounts for the evolution from trachyte to alkali-trachyte magmas; these were intimately mingled (at the micrometer scale) during the climactic phase of the eruption. The Averno 2 alkali trachyte represents one of the most evolved magmas erupted within the Phlegraean Fields area and belongs to the series of differentiated trachytic magmas erupted at different locations 5 ka ago. Melt inclusions record significant variations in H2O (from 0.4 to 5 wt%), S (from 0.01 to 0.06 wt%), Cl (from 0.75 up to 1 wt%), and F (from 0.20 to >0.50 wt%) during both magma crystallization and degassing. Unlike the eruptions occurring in the central part of the PFc, deep-derived input(s) of gas and/or magma are not required to explain the composition of melt inclusions and the mineralogy of Averno 2 pumices. Compositional data on bulk pumices, glassy matrices, and melt inclusions suggest that the Averno 2 eruption mainly resulted from successive extrusions of independent magma batches probably emplaced at depths of 2–4 km along regional fractures bordering the Neapolitan Yellow Tuff caldera.219 25 - PublicationRestrictedSimultaneous eruptions from multiple vents at Campi Flegrei (Italy) highlight new eruption processes at calderas(2016)
; ; ; ; ; ; ; ; ; ; ;; ;; ; ; ; ; ;Volcanic eruptions are typically characterized by the rise and discharge of magma at the surface through a single conduit-vent system. However, in some cases, the rise of magma can be triggered by the activation of eruptive fissures and/or vents located several kilometers apart. Simultaneous eruptions from multiple vents at calderas, not related to caldera collapse (e.g., ring faults), are traditionally regarded as an unusual phenomenon, the only historically reported examples occurring at Rabaul caldera, Papua New Guinea. Multiple venting within a caldera system is inherently difficult to demonstrate, owing partly to the infrequency of such eruptions and to the difficulty of documenting them in time and space. We present the first geological evidence that at 4.3 kyr B.P., the Solfatara and Averno vents, 5.4 km apart, erupted simultaneously in what is now the densely populated Campi Flegrei caldera (southern Italy). Using tephrostratigraphy and geochemical fingerprinting of tephras, we demonstrate that the eruptions began almost at the same time and alternated with phases of variable intensity and magnitude. The results of this study demonstrate that multi-vent activity at calderas could be more common than previously thought and volcanic hazards could be greater than previously evaluated. More generally we infer that the simultaneous rise of magma and gas along different pathways (multiple decrepitation of chamber[s]) could result in a sudden pressure rise within the sub-caldera magmatic system.91 3