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Barde-Cabusson S.,CSIC - Institute of Earth Sciences Jaume Almera | Gottsmann J.,University of Bristol | Marti J.,CSIC - Institute of Earth Sciences Jaume Almera | Bolos X.,CSIC - Institute of Earth Sciences Jaume Almera | And 5 more authors.
Bulletin of Volcanology | Year: 2014

We report new geophysical observations on the distribution of subsurface structures associated with monogenetic volcanism in the Garrotxa volcanic field (Northern Spain). As part of the Catalan Volcanic Zone, this Quaternary volcanic field is associated with the European rifts system. It contains the most recent and best preserved volcanic edifices of the Catalan Volcanic Zone with 38 monogenetic volcanoes identified in the Garrotxa Natural Park. We conducted new gravimetric and self-potential surveys to enhance our understanding of the relationship between the local geology and the spatial distribution of the monogenetic volcanoes. The main finding of this study is that the central part of the volcanic field is dominated by a broad negative Bouguer anomaly of around -0.5 mGal, within which a series of gravity minima are found with amplitudes of up to -2.3 mGal. Inverse modelling of the Bouguer data suggests that surficial low-density material dominates the volcanic field, most likely associated with effusive and explosive surface deposits. In contrast, an arcuate cluster of gravity minima to the NW of the Croscat volcano, the youngest volcano of this zone, is modelled by vertically extended low-density bodies, which we interpret as a complex ensemble of fault damage zones and the roots of young scoria cones. A ground-water infiltration zone identified by a self-potential anomaly is associated with a steep horizontal Bouguer gravity gradient and interpreted as a fault zone and/or magmatic fissure, which fed the most recent volcanic activity in the Garrotxa. Gravimetric and self-potential data are well correlated and indicate a control on the locations of scoria cones by NNE-SSW and NNW-SSE striking tectonic features, which intersect the main structural boundaries of the study area to the north and south. Our interpretation of the data is that faults facilitated magma ascent to the surface. Our findings have major implications for understanding the relationship between subsurface structures and potential future volcanic activity in the Garrotxa volcanic field. © 2013 European Union. Source


Bartolini S.,CSIC - Institute of Earth Sciences Jaume Almera | Bolos X.,CSIC - Institute of Earth Sciences Jaume Almera | Marti J.,CSIC - Institute of Earth Sciences Jaume Almera | Pedra E.R.,CSIC - Institute of Earth Sciences Jaume Almera | Planaguma L.,TOSCA
Natural Hazards | Year: 2015

La Garrotxa Volcanic Field (GVF) in the NE Iberian Peninsula is one of the Quaternary alkaline volcanic provinces that form part of the European Cenozoic Rift System. Active over the last 0.7 Ma, the most recent dated eruption in this volcanic zone took place in the early Holocene (11–13 ka). Its volcanic activity has varied from Hawaiian to violent Strombolian, with numerous episodes of phreatomagmatic activity, and is controlled by the main regional normal faults generated during the Neogene extension that affected the area. Despite the potential for future eruptions and the fact that this is a densely populated industrial area, no volcanic hazard assessment of the field has ever been conducted. In this work, we present the first comprehensive evaluation of the volcanic hazard in the GVF via (1) an evaluation of its volcanic susceptibility, (2) a temporal recurrence rate analysis, (3) a simulation of different eruptive scenarios, such as lava flows, pyroclastic density currents and ashfall, and (4) the elaboration of a qualitative hazard map. The final hazard map shows that the GVF can be subdivided into five different hazard levels, knowledge that will be useful for land-use management and the drawing up of emergency plans. © 2015, Springer Science+Business Media Dordrecht. Source


Marti J.,CSIC - Institute of Earth Sciences Jaume Almera | Planaguma L.,TOSCA | Geyer A.,International Center for Numerical Methods in Engineering | Canal E.,TOSCA | Pedrazzi D.,CSIC - Institute of Earth Sciences Jaume Almera
Journal of Volcanology and Geothermal Research | Year: 2011

The Catalan Volcanic Zone (CVZ), at the NE of the Iberian peninsula, is one of the Quaternary alkaline volcanic provinces of the European rifts system. The CVZ has been active during the last 12Ma. Despite the fact that this volcanism is significant in extension and volume, and that eruptions have also occurred in Holocene times, it is mostly unknown compared to the contemporaneous alkaline volcanism in other parts of Western and Central Europe. Volcanism younger than 0.5Ma is mostly concentrated in an area of about 100km 2 located between the main cities of Olot and Girona. This basaltic volcanic field comprises more than 50 monogenetic cones including scoria cones, lava flows, tuff rings, and maars. Magmatic eruptions range from Hawaiian to violent Strombolian. Phreatomagmatism is also common and has contributed to the construction of more than a half of these volcanic edifices, frequently associated with the Strombolian activity but also independently, giving rise to a large variety of eruptive sequences. We describe the main characteristics of this volcanism and analyse in particular the successions of deposits that form some of these volcanoes and discuss the potential causes of such a wide diversity of eruptive sequences. We find that the main cause of such complex eruptive behaviour resides in the stratigraphic, structural and hydrogeological characteristics of the substrate above which the volcanoes were emplaced, rather than on the compositional characteristics of the erupting magma, as they do not show significant variations among the different volcanoes studied. © 2010 Elsevier B.V. Source


Morawa Eblagon K.,University of Oxford | Tam K.,Astrazeneca | Yu K.M.K.,University of Oxford | Zhao S.-L.,East China University of Science and Technology | And 6 more authors.
Journal of Physical Chemistry C | Year: 2010

Hydrogen storage is a significant challenge for the development and viability of hydrogen-powered vehicles. Storage of molecular hydrogen in nitrogen-substituted polyunsaturated aromatic organic molecules through reversible catalytic hydrogenation and dehydrogenation is a promising approach. The success of developing a catalytic hydrogen storage concept is highly dependent on finding an efficient catalyst; however, understanding how molecules interact with metal catalytic sites is, at present, rather limited. In this work, a combined experimental and theoretical study is conducted to identify efficient catalytic sites on metallic surfaces and to understand the reaction mechanism for the forward hydrogenation reaction. It is clearly revealed from experimentation that hydrogenation of N-ethylcarbazole, a typical nitrogen-substituted polyunsaturated aromatic organic molecule, is taking place in a stepwise manner over metal catalysts. Because of steric constraints at terrace sites, the kinetically stable pyrrole intermediate, formed by partial hydrogenation of N-ethylcarbazole, cannot be readsorbed once desorbed into solution. Therefore further hydrogenation occurs at the low coordinated sites where no similar steric hindrance is encountered. Thus, the mechanism for hydrogenation involves an unusual shuttling of partially hydrogenated intermediates from terrace sites to higher indexed sites via solution. First-principles calculations confirm that the pyrrole intermediate can strongly adsorb to various low coordination sites, typically steps on the vicinal (109) surface, while the adsorption is extremely weak on flat (001) terraces. This work is the first example of catalytic site analysis to account for observed activity, selectivity and recyclability of a typical metal catalyst for catalytic hydrogen storage, which could lead to rational design of superior materials. © 2010 American Chemical Society. Source

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