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Authors: Madonia, Paolo 
Issue Date: 28-May-2009
Keywords: Eruption
Subject Classification04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous 
Abstract: Volcanic activity is considered one of the possible causes for mass extinctions occurred during the geologic history of the Earth. Volcanic products from high energetic explosive eruptions, ejected up to the stratosphere and dispersed worldwide or on a regional scale by atmospheric currents, may significantly change the amount of solar irradiance received at ground level, causing dramatic climatic changes on their own responsible for the mass extinctions. The amount of energy, i.e. the amount of magma involved in the eruption, needed for such a kind of phenomena is not (fortunately for vivents) generable by all the volcanoes, but only by a category of large dimension structure known as “supervolcanoes”. The most famous actual supervolcano is the Yellowstone Caldera, located in Central USA, potentially able to generate an eruption so energetic to cause the partial or total extinction of the most of the vivents of the entire world. On a smaller spatial and energetic scale, one of the volcanic eruptions that changed the climatic scenery of the northern emisphere was from the Hekla volcano (Iceland) in the XVIII century, whose products were dispersed up to the African continent. One of the long lasting effects of this eruption could have been the formation of a permanent ice body into a cave on Mt.Etna (Sicily), known as “Grotta del Gelo (Frost Cave)”, representing today the southernmost permanent ice accumulation of the northern emisphere. Another possible cause for mass extinctions is the simultaneous eruption of several volcanoes, possibly triggered by a common cause. Recent studies based on spatial geodesy demonstrated that, at global terrestrial scale, the shallower portion of the solid Earth, better known as “crust”, is affected by vertical displacements of the order of few centimetres, induced by the combined effects of atmospheric pressure, its water content, ice and snow coverage at high latitudes, etc. Inflation and deflation cycles of the crust are theoretically able to cause permeability variations of the rocky masses, on their own favouring fluid (including magmas) migrations inside the Earth; statistical studies on the occurrence of volcanic eruptions seem to account for this being one of the possible common triggers for volcanic activity. At regional scale, acceleration of displacement rates between tectonic plates may act as trigger for tectono-volcanic systems located close to the plates boundary, as it seems happened in the South Mediterranean area during the years 2002-03. Possible triggers for volcanic systems may also be of extra-terrestrial origin, with particular reference to the perturbation induced by the solar wind in the high strata of the terrestrial atmosphere (ionosphere). Under certain conditions it seems possible the activation of a propagation chain that, from the ionosphere through the troposphere, could extend the perturbation front down to the lithosphere, influencing that volcanic systems whose activity state is high enough to react to these low-energy stresses.
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