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Hydrmagmatic monogenetic volcanism in continental and oceanic island enronments

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Universitat de Barcelona. Facultat de Geologia

# metadata.dc.description.abstract[].value
[spa] El vulcanismo monogenético se caracteriza por una gran diversidad de estilos eruptivos, morfologías y depósitos. Los tipos de edificios que se forman son el resultado de una compleja combinación de parámetros que rigen la física de la erupción. La atención de este trabajo se centra en la relación entre los edificios volcánicos monogenéticos y las variables externas que influyen en la dinámica de las erupciones (es decir, magmatismo vs freatomagmatismo) a través de un punto de vista multidisciplinar, en ambientes continentales y marinos en los que el vulcanismo puede desarrollar. Diferentes estudios, representativos de este tipo de actividad en diferentes entornos geográficos y geológicos, se han llevado a cabo. El primer ejemplo corresponde al volcán de La Crosa de Sant Dalmai (Campo Volcánico de La Garrotxa) donde se han reconstruido las condiciones hidrogeológicas del sustrato y la implicación para la dinámica eruptiva. Como segundo caso de estudio, se ha realizado una estratigrafía de detalle del cono de toba de El Golfo (Lanzarote, Islas Canarias), donde se han estudiado los mecanismos de emplazamiento de los depósitos para inferir cambios en la interacción magma/agua. Otro tipo de erupción se ha investigado en el mismo archipiélago, en la Isla de El Hierro, determinando las características físicas de un episodio félsico de origen hidrovolcánico ocurrido en una isla que se caracteriza esencialmente por el vulcanismo basáltico tanto Estromboliano como Hawaiiano. Por último, este mismo tipo de metodología se ha aplicado a la Isla Decepción (archipiélago de las Shetland del Sur, Antártida), estableciendo los parámetros físicos de la erupción del 1970 con el fin de comparar este episodio con el evento anterior del 1967, y deducir sus consecuencias para llevar a cabo la evaluación de peligrosidad en la isla. Los resultados obtenidos pueden ser aplicados a campos volcánicos monogenéticos en todo el mundo y, por tanto, son útiles para reconstruir la evolución de ciertos campos volcánicos, a través del estudio de volcanes monogenéticos individuales, para evaluar los posibles riesgos volcánicos, teniendo en cuenta como erupciones similares representan una grave amenaza, que es a menudo subestimada.

# metadata.dc.description.abstract[].value
[eng] Monogenetic volcanism is characterized by a large diversity of eruptive styles, morphologies and deposits. Monogenetic landforms are the result of a complex merging of internal (magma composition, vesiculation) and external (geological setting, fracturation, hydrogeology, substrate stratigraphy, etc) parameters that govern the physics of the eruptions. Changes in these parameters may cause variations in the eruption style several times during the course of such short-lived volcanoes. Monogenetic volcanoes may form in any type of geological environment with scoria cones being the most common volcano type and hydrovolcanic tuff rings, tuff cones, and maars as the second in abundance. These small-volume volcanoes are generally the result of short-lived eruptions but the activity in a monogenetic volcanic field might exceed the total life of composite volcanoes. The attention of this work was focused on the relation between monogenetic volcanic landforms and the external variables that influenced the dynamics of the eruptions (i.e. magmatism vs phreatomagmatism) through a multidisciplinary perspective, in marine and continental geological settings under which monogenetic volcanism may develop. Different case studies representative of this type of activity and of these different environments have been considered. The first one corresponds to the La Crosa De Sant Dalmai volcano (Garrotxa Volcanic Field, southern sector of the Catalan Volcanic Zone), a roughly circular asymmetrical maar-diatreme volcano, which is one of the most characteristic volcanic edifices of this continental monogenetic volcanic field and the largest Quaternary volcanic crater on the Iberian Peninsula. This edifice is an example of monogenetic landform, mostly composed of phreatomagmatic deposits with subordinate Strombolian phases, constructed on a mixed basement made of hard Paleozoic granites and schists rocks and soft Plio-Quaternary deposits. Here, I reconstructed the hydrogeological conditions of the substrate and the implication for the eruptive dynamics. As a second case study, I carried out detailed stratigraphic and sedimentological studies of the succession of El Golfo tuff cone (Lanzarote, Canary Islands). The main objective of the work was to describe in detail the structure and association of facies of this edifice and use this information to infer changes in eruption style and depositional processes. Another type of eruption was studied in the same archipelago at El Hierro, an island essentially characterized by basaltic volcanism with both Strombolian and Hawaiian activity. Here I reported the stratigraphic, lithological, sedimentological and petrographic characteristics of a felsic hydrovolcanic episode in order to discuss, transport/depositional mechanisms, dynamics, relative age and implications for hazard assessment on the island. Finally, the same type of methodology was applied at Deception Island (Southern Shetland Archipelago, Antarctica), determining the lithological and sedimentological characteristics, and clasts distribution (isopach and isopleth maps) of the eruption of 1970. This information was, then, used to determine depositional processes, eruption style and physical parameters (i.e. plume height, erupted volume, VEI) of the eruption in order to compare this episode with the previous 1967 episode, and to deduce their implications to conduct hazard assessment at the island. Each work represents a diverse aspect of hydrovolcanism and the results obtained helped to better understand the eruptive behavior of this type of volcanoes, which is a fundamental task in order to understand the possible future hazards associated with this type of volcanism. The results obtained can be applied to monogenetic volcanic fields worldwide and are, therefore, useful to reconstruct the evolution of a certain volcanic fields, through the study of single monogenetic volcanoes, and to evaluate the possible volcanic hazards, as similar eruptions represent a serious threat, which is often underestimated. A more systematic study is, thus, needed in order to understand the role of shallow-level conditions in the formation of specific volcano types in such complex volcanic fields.

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Tesis Doctorals - Facultat - Ciències de la Terra

# metadata.dc.title[].value
Hydrmagmatic monogenetic volcanism in continental and oceanic island enronments