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Martí, Joan
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Martí, Joan
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- PublicationOpen AccessIncrement in the volcanic unrest and number of eruptions after the 2012 large earthquakes sequence in Central America(2021-11-17)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ;Understanding the relationship cause/effect between tectonic earthquakes and volcanic eruptions is a striking topic in Earth Sciences. Volcanoes erupt with variable reaction times as a consequence of the impact of seismic waves (i.e. dynamic stress) and changes in the stress field (i.e. static stress). In 2012, three large (Mw ≥ 7.3) subduction earthquakes struck Central America within a period of 10 weeks; subsequently, some volcanoes in the region erupted a few days after, while others took months or even years to erupt. Here, we show that these three earthquakes contributed to the increase in the number of volcanic eruptions during the 7 years that followed these seismic events. We found that only those volcanoes that were already in a critical state of unrest eventually erupted, which indicates that the earthquakes only prompted the eruptions. Therefore, we recommend the permanent monitoring of active volcanoes to reveal which are more susceptible to culminate into eruption in the aftermath of the next large-magnitude earthquake hits a region.165 8 - PublicationRestrictedRemarkable variability in dyke features at the Vicuña Pampa Volcanic Complex, Southern Central Andes(2017-09)
; ; ; ; ; ; ; ; ; ; ; ; ; Dykes at the Vicuña Pampa Volcanic Complex, which are mostly basaltic (trachy)-andesite and (trachy)-andesite, are exposed at the base and along the walls of a large depression resulting from intense degradation. Dykes intruding stiff layers (lavas, plugs and necks) are thin, mostly dip >60° and have coherent textures, whereas dykes intruding more compliant materials (breccias and conglomerates) tend to be thicker, have lower dips and have coherent, brecciated or mixed textures (coherent and brecciated textural domains in a single or compound dyke). Single dykes with brecciated and mixed textures are only found intruding near-surface units. Dykes with mixed textures always have sharp contacts between domains. Dykes with sinuous domain contacts and enclaves of one domain inside the other are interpreted as resulting from dyke arrest, partial cooling and reinjection of new magma. Dykes with straight domain contacts are considered to be compound dykes, with a new dyke intruding along the margins of an older, solidified one.648 3 - PublicationOpen AccessStress Field Control during Large Caldera-Forming EruptionsCrustal stress field can have a significant influence on the way magma is channeled through the crust and erupted explosively at the surface. Large Caldera Forming Eruptions (LCFEs) can erupt hundreds to thousands of cubic kilometers of magma in a relatively short time along fissures under the control of a far-field extensional stress. The associated eruption intensities are estimated in the range 109–1011 kg/s. We analyse syn-eruptive dynamics of LCFEs, by simulating numerically explosive flow of magma through a shallow dyke conduit connected to a shallow magma (3–5 km deep) chamber that in turn is fed by a deeper magma reservoir (>∼10 km deep), both under the action of an extensional far-field stress. Results indicate that huge amounts of high viscosity silicic magma (>107 Pa s) can be erupted over timescales of a few to several hours. Our study provides answers to outstanding questions relating to the intensity and duration of catastrophic volcanic eruptions in the past. In addition, it presents far-reaching implications for the understanding of dynamics and intensity of large-magnitude volcanic eruptions on Earth and to highlight the necessity of a future research to advance our knowledge of these rare catastrophic events.
63 69 - PublicationOpen AccessTemporal evolution of flow conditions in sustained magmatic explosive eruptions(2005)
; ; ; ; ;Macedonio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Neri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Centro per la Modellistica Fisica e Pericolosita` dei Processi Vulcanici ;Marti, J.; Istitut de Ciences de le Terra Jaume Almera, CSIC, Barcelona, Spain ;Folch, A.; Istitut de Ciences de le Terra Jaume Almera, CSIC, Barcelona, Spain; ; ; The temporal evolution of fundamental flow conditions in the magma chamber plus conduit system–such as pressure, velocity, mass flow-rate, erupted mass, etc.–during sustained magmatic explosive eruptions was investigated. To this aim, simplified one-dimensional and isothermal models of magma chamber emptying and conduit flow were developed and coupled together. The chamber model assumed an homogeneous composition of magma and a vertical profile of water content. The chamber could have a cylindrical, elliptical or spherical rigid geometry. Inside the chamber, magma was assumed to be in hydrostatic equilibrium both before and during the eruption. Since the time-scale of pressure variations at the conduit inlet–of the order of hours–is much longer than the travel time of magma in the conduit–of the order of a few minutes–the flow in the conduit was assumed as at steady-state. The one dimensional mass and momentum balance equations were solved along a circular conduit with constant diameter assuming choked-flow conditions at the exit. Bubble nucleation was considered when the homogeneous flow pressure dropped below the nucleation pressure given the total water content and the solubility law. Above the nucleation level, bubbles and liquid magma were considered in mechanical equilibrium. The same equilibrium assumption was made above the fragmentation level between gas and pyroclasts. Due to the hydrostatic hypothesis, the integration of the density distribution in the chamber allowed to obtain the total mass in the chamber as a function of pressure at the chamber top and, through the conduit model, as a function of time. Simulation results pertaining to rhyolitic and basaltic magmas defined at the Volcanic Eruption Mechanism Modeling Workshops (Durham, NH, 2002; Nice, France, 2003) are presented. Important flow variables, such as pressure, density, velocity, shear stress in the chamber and conduit, are discussed as a function of time and magma chamber and conduit properties. Results indicate that vent variables react in different ways to the pressure variation of the chamber. Pressure, density and mass flow-rate show relative variations of the same order of magnitude as the conduit inlet pressure, whereas velocity is more constant in time. Sill-like chambers produce also significantly longer and more voluminous eruptions than dike-like chambers. Water content stratification in the chamber and the increase of chamber depth significantly reduce the eruption duration and volume. Maximum erupted mass fractions of about 0.2 are computed for small water-saturated and shallow chambers.289 92 - PublicationRestrictedGeoethics: The Missing Piece in the Separation of Responsibility Between Volcanologists and Decision-Makers(Springer, 2023-04-21)
; ; ; ; ; ; ; ; ; ; ; ; ;In a volcanic crisis, authorized decision-makers must balance the social and economic costs of mitigating actions, such as evacuation, against the potential human losses if such actions are insufficient. In making their decisions, advice is needed from volcanologists on the eruption probability. Therefore, there should be a clear separation in the roles of volcanologists and decision-makers; the volcanologists should advise on the volcano hazard and alternative potential scenarios but refrain from involvement in making decisions. Currently, volcanologists are responsible for setting volcano alert levels. Given the small handful of distinct alert levels, there is inherent ambiguity and substantial uncertainty in the interpretation of individual levels. Furthermore, changing an alert level may automatically trigger actions by decision-makers. This would violate the principle of separation of responsibility and may result in unwelcome pressure being applied to volcanologists. Just as physicians can invoke medical ethics in resisting pressure to alter their advice, so volcanologists can invoke geoethics. Freedom to abide by their scientific beliefs is a basic tenet of geoethics.54 5 - PublicationOpen AccessEditorial: Volcanic Islands—A Challenge for Volcanology(2022-06-22)
; ; ; ; ; ; ; Most volcanoes on the Earth rise from the bottom of seas and oceans. Most of them do not reach the surface of sea and remain hidden to all conventional observations from surface and space. Only some of them rise above the sea level, forming islands and passing from submarine to subaerial volcanism. Volcanic islands develop in virtually all the geodynamic contexts on Earth, from mid-ocean ridges (Iceland), to intraplate (Hawaii), to volcanic arcs (Aeolian Islands). All the liquid-descent evolutive degrees of magma are finally represented, from primitive compositions up to strongly evolved rhyolite, trachyte and phonolite lavas. So, the eruptive styles of these volcanoes range consequently from mild effusions to plinian eruptions.649 12 - PublicationRestrictedQVAST: a new Quantum GIS plugin for estimating volcanic susceptibility(2013-11-27)
; ; ; ; ;Bartolini, S.; Institute of Earth Sciences Jaume Almera, ICTJA-CSIC, Barcelona, Spain ;Cappello, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Martì, J.; Institute of Earth Sciences Jaume Almera, ICTJA-CSIC, Barcelona, Spain ;Del Negro, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; ; ; One of the most important tasks of modern volcanology is the construction of hazard maps simulating different eruptive scenarios that can be used in risk-based decision making in land-use planning and emergency management. The first step in the quantitative assessment of volcanic hazards is the development of susceptibility maps (i.e., the spatial probability of a future vent opening given the past eruptive activity of a volcano). This challenging issue is generally tackled using probabilistic methods that use the calculation of a kernel function at each data location to estimate probability density functions (PDFs). The smoothness and the modeling ability of the kernel function are controlled by the smoothing parameter, also known as the bandwidth. Here we present a new tool, QVAST, part of the open-source geographic information system Quantum GIS, which is designed to create user-friendly quantitative assessments of volcanic susceptibility. QVAST allows the selection of an appropriate method for evaluating the bandwidth for the kernel function on the basis of the input parameters and the shapefile geometry, and can also evaluate the PDF with the Gaussian kernel. When different input data sets are available for the area, the total susceptibility map is obtained by assigning different weights to each of the PDFs, which are then combined via a weighted summation and modeled in a non-homogeneous Poisson process. The potential of QVAST, developed in a free and user-friendly environment, is here shown through its application in the volcanic fields of Lanzarote (Canary Islands) and La Garrotxa (NE Spain).209 45 - PublicationRestrictedConstruction and degradation of a broad volcanic massif: The Vicuña pampa volcanic complex, southern central Andes, NW Argentina(2017-05)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ;The Vicuña Pampa volcanic complex, at the SE edge of the arid Puna Plateau of the Central Andes, records the interplay between volcanic construction and degradational processes. The low-sloping Vicuña Pampa volcanic complex, with a 1200-mdeep, southeastward- opening depression, was previously interpreted as a collapse caldera based on morphological considerations. However, characteristic features associated with collapse calderas do not exist, and close inspection instead suggests that the Vicuña Pampa volcanic complex is a strongly eroded, broad, massif-type composite volcano of mainly basaltic to trachyandesitic composition. Construction of the Vicuña Pampa volcanic complex occurred during two distinct cycles separated by the development of the depression. The first and main cycle took place at ca. 12 Ma and was dominated by lava flows and subordinate scoria cones and domes. The second cycle, possibly late Mio-cene in age, affected the SW portion of the depression with the emplacement of domes. We interpret the central depression as the result of a possible sector collapse and subsequent intense fluvial erosion during middle to late Miocene time, facilitated by faulting, steepened topography, and wetter climate conditions compared to today. We estimate that ~65% of the initial edifice of ~240 km3 was degraded. The efficiency of degradation processes for removing mass from the Vicuña Pampa volcanic complex is surprising, considering that today the region is arid, and the stream channels within the complex are predominantly transport limited, forming a series of coalesced, aggraded alluvial fans and eolian infill. Hence, the Vicuña Pampa volcanic complex records the effects of past degradation efficiency that differs substantially from that of today.617 3