Hidden Tectonic Framework Of The Summit Of Mt.Etna (Sicily, Italy) Revealed From Soil CO2 Efflux And Soil Temperature Surveying.

Abstract

Mount Etna in Sicily (973 km2), the most active European volcano, is known as one of the largest contributors of magmatic CO2 released to the atmosphere. A significant part of this gas is released in diffuse form through the volcano’s flanks, along faults and fractured zones, particularly around its summit (about 3350 m). Etna is also characterized by significant and often dramatic slope failure of its eastern flank, which is thought to trigger summit collapses and some lateral eruptions. In order to map the faulted areas near Etna’s summit and to study possible weak zones, a diffuse CO2 efflux survey was carried out at Mt. Etna in October, 2008. A total of 1442 sites were surveyed for soil CO2 efflux and soil temperature over an area of about 9 km2 that included most of the summit part of Mt. Etna above 2600 m a.s.l. The results show the presence of several degassing faults in all of the surveyed area except its west part, which seems to be structurally stable. Most of the degassing faults start from the summit craters and run parallel to the borders of the eastward collapsing sector of the volcano. Many of them are related to the development of the South-East Crater, but others seem to be related to a large buried crater rim, probably a remnant of the 1669 collapse crater formed during the largest eruption in the last 2000 years. Some degassing faults are not accompanied by thermal anomalies, thus suggesting that the gas source is too deep and/or the ground permeability is too low to allow high-enthalpy fluids to reach the surface before their condensation. These “cold” faults bound the anomalous degassing areas to the west, therefore they would be relatively new and shallow, suggesting a progressive westward shift of slope failure.