Continuous Monitoring Of Soil Radon Activity And Soil Temperature Near The Summit Of Mt. Etna (Sicily, Italy) During 2007-2009: Correlations With Stress Field And Volcanic Activity

Abstract

During the period 2007-2009, the volcanic activity of Mt. Etna (Italy) was characterized by a series of paroxysmal events in 2007 that preceded a long-lasting (419 days) flank eruption. Four months after the end of that eruption, the opening of a new summit degassing vent marked the beginning of a new phase of activity, so far characterized only by degassing phenomena. Soil radon activity and soil temperature were monitored every 15 minutes at a low-temperature fumarole near the summit craters of Etna starting from late May 2007. The temporal pattern of these parameters showed in general their significant cross-correlation, thus pointing to a common gas transport mechanism. Magmatic/ hydrothermal fluids in the sub-surface ground are convectively transported towards the surface along a major fault that runs from Etna’s summit towards SSE and partly marks the boundary of an eastward sliding sector of the volcano that is involved into phenomena of flank collapse. Both of the monitored parameters indicate the occurrence of three long-term cycles of soil degassing during the period investigated, each one characterized by high average values of temperature and radon. The first cycle started in June 2007 and lasted until early April 2008, thus accompanying the recharge of the volcano. The second cycle lasted from late April 2008 to mid-May 2009, thus preceding and accompanying the first phase of the 13 May 2008 – 5 July 2009 flank eruption. The third cycle started in mid-July 2009 and it’s still ongoing. It marked a new recharge of the volcano that culminated in the opening of the new summit degassing vent in early November 2009. Therefore, continuous monitoring of soil radon and soil temperature near the summit of Mt. Etna has proven helpful in determining states of volcanic unrest related to recharge and/or pre-eruptive magma ascent.