HR: 08:00h
AN: V31A-01 INVITED     [Abstracts]
TI: What is a volcano?
AU: * Borgia, A
EM: andrea.borgia@edra.us
AF: EDRA, via di Fioranello 31, Roma, 00134, Italy
AU: Merle, O
EM: O.Merle@opgc.univ-bpclermont.fr
AF: Département de Sciences de la Terre, Université Blaise Pascal, 5, rue Kessler, Clermont Ferrand, 63083, France
AU: van Wyk de Vries, B
EM: b.vanwyk@opgc.univ-bpclermont.fr
AF: Département de Sciences de la Terre, Université Blaise Pascal, 5, rue Kessler, Clermont Ferrand, 63083, France
AU: Aubert, M
EM: m.aubert@opgc.univ-bpclermont.fr
AF: Département de Sciences de la Terre, Université Blaise Pascal, 5, rue Kessler, Clermont Ferrand, 63083, France
AB: In a volcano, magma, generated at a source in a planetary interior, flows upward with varying amounts of physicochemical evolution, intruding the encasing rocks. Once near the top of the lithosphere, that is at a major rigid-fluid, high-low-density interface, the magma erupts, piercing this interface. While gas, vapors and thinnest particles mix up with the atmosphere and stratosphere, larger drops and particles will eventually accumulate on top of the interface to form volcanic deposits, giving rise in the area around the crater to a volcanic edifice. In turn, these deposits may be intruded or modified by magma, eruptions, geothermal fluids, tectonics, erosion, landsliding and all other kinds of geologic processes. In this view, volcanism is a self-similar process that ranges many orders of magnitude in space and time scales from small cinder cones to large ocean ridges. For instance, at Amiata Volcano, Italy, many of the above mentioned processes have interacted. The volcano is deeply dissected by volcanic spreading, to the point of loosing its original cone-like shape; large diapirs and thrust-related structure have formed in the clay- and gypsum-rich substratum all around the volcano generating dismembered lava flows. In addition, the spreading have created the conditions for the existence of mercury mineralization and geothermal reservoirs. All this complexity that, in our opinion must be considered volcanic is not easy described by commonly used definitions of volcanoes. In fact, former definitions of "volcano", for instance that from the Glossary of Geology (1997) "a vent in the surface of the Earth through which magma and associated gases and ash erupt" or "the form or structure, usually conical, that is produced by the ejected material" are clearly insufficient and cannot capture the geologic complexity of a real volcanic environment. All definitions, that we encountered, tend to consider volcanoes from the point of view of a single discipline, each of them neglecting relevant aspects belonging to other disciplines. For the two cases mentioned above a volcano is seen only from the point of view of eruptive activity or of morphology. We attempt to look at "volcano" holistically to provide a more comprehensive definition. We define a volcano as a geologic environment that, at any scale, is characterized by three elements: magma, eruption and edifice. It is sufficient that only one of these elements is proven, as long as the others can be inferred to exist, to have existed, or that will exist.
DE: 6924 Interferometry (1207, 1209, 1242)
DE: 8003 Diapir and diapirism
DE: 8135 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8424)
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
DE: 8425 Effusive volcanism
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly