No abstract

Rn highlights sites of ongoing shallow rock fracturing that could be affected by collapse, as in the case of the rim of an active vent. Depletion both in 220 Rn and in CO 2 seems to be representative of residual degassing along recently active eruptive vents.

Five years of gas monitoring from selected sites suggest that Mt Etna's plumbing system is much more extensive than previously reported. It extends at least 40 km SW from the volcano's boundary along the NE‐SW regional fault, where it discharges about 200 tons/day of gas, containing helium with mantle‐type isotopic composition. Synchronous variations of 3He/4He isotopic ratios in gas sampled at sites located 60 kilometers apart have allowed us to detect pulses of ascending magma in the plumbing system, thus providing a powerful tool for eruption forecasting. Following summer 2001 eruption, the still increasing trend of the 3He/4He ratios indicates that magma storage is even now occurring at a shallow depth. Hence, the volcano maintains a high capacity to re‐erupt within the next few months.

No abstract

Continuous soil radon monitoring was carried out near the Southeast Crater (SEC) of Mt. Etna during the 10‐day July 2006 Strombolian‐effusive eruption. This signal was compared with simultaneously acquired volcanic tremor and thermal radiance data. The onset of explosive activity and a lava fountaining episode were preceded by some hours with increases in radon soil emission by 4–5 orders of magnitude, which we interpret as precursors. Minor changes in eruptive behavior did not produce significant variations in the monitored parameters. The remarkably high radon concentrations we observed are unprecedented in the literature. We interpret peaks in radon activity as due primarily to microfracturing of uranium‐bearing rock. These observations suggest that radon measurements in the summit area of Etna are strongly controlled by the state of stress within the volcano and demonstrate the usefulness of radon data acquisition before and during eruptions.

The relationships between soil gas emissions and both tectonic and volcano-tectonic structures on Mt. Etna have been studied. The investigation consisted of soil CO 2 flux measurements along traverses orthogonal to the main faults and eruptive fissures of the volcano. Anomalous levels of soil degassing were found mainly in coincidence with faults, whereas only 49% of the eruptive fissures were found to produce elevated CO 2 soil fluxes. This result suggests that only zones of strain are able to channel deep gases to the surface. According to this hypothesis, several previously unknown structures are suggested. Based on our geochemical data, new structural maps of different areas of Etna are proposed. The soil CO 2 fluxes observed in this study are higher than those measured in a 1987 study, and they are consistent with the higher level of volcanic unrest during the current study.

No abstract

After 16 months of quiescence, Mount Etna began to erupt again in mid-July 2006. The activity was concentrated at and around the Southeast Crater (SEC), one of the four craters on the summit of Etna, and eruptive activity continued intermittently for 5 months. During this period, numerous vents displayed a wide range of eruptive styles at different times. Virtually all explosive activities took place at vents at the summit of the SEC and on its flanks. Eruptive episodes, which lasted from 1 day to 2 weeks, became shorter and more violent with time. Volcanic activity at these vents was often accompanied by dramatic mass-wasting processes such as collapse of parts of the cone, highly unusual flowage processes involving both old rocks and fresh magmatic material, and magmawater interaction. The most dramatic events took place on 16 November, when numerous rockfalls and pyroclastic density currents (PDCs) were generated during the opening of a large fracture on the SE flank of the SEC cone. The largest PDCs were clearly triggered explosively, and there is evidence that much of the energy was generated during the interaction of intruding magma with wet rocks on the cone's flanks. The most mobile PDCs traveled up to 1 km from their source. This previously unknown process on Etna may not be unique on this volcano and is likely to have taken place on other volcanoes. It represents a newly recognized hazard to those who visit and work in the vicinity of the summit of Etna.