Stromboli is one of the most active volcanoes on Earth, and one of the few where passive degassingpersistently coexists with the (non-passive) release of over-pressurized gas pockets during bothexplosions and gas puffing activity. These transient gas bursting-puffing phenomena are difficultto study by conventional spectroscopic scanning techniques (e.g., DOAS), since these have far toolow temporal resolution. Here, we take advantage of the high spatial and time resolution (0.6-1 Hz)of the recently developed UV camera technique to obtain a simultaneous characterisation of all thedifferent forms of SO2 release at Stromboli (including passive degassing, Strombolian eruptions andpuffing).During a field campaign from 10th to 16th July, 2010, we observed at Stromboli a total SO2 fluxaveraging at ~ 70 t·d-1, but also showing large (10-30 t·d-1) cyclic fluctuations with periodicity of400-1000 seconds. This periodic degassing behaviour, which was recently also detected at Mt. Etna,Erebus and Fuego, may be a systematic feature of basaltic volcanoes; a fact which - if confirmed -would bring profound implications for models of magma-gas flow in conduits, and for generation ofbasaltic explosions.These periodic SO2 flux variations were punctuated by brief SO2 flux peaks in coincidence withexplosions. We obtained UV camera observations for 130 discrete explosions overall, and wefound that the erupted SO2 mass per explosion ranged 2-55 kg, and averaged at ~20 kg. Thiscorresponds to a daily explosive SO2 output rate of 4.2 ± 1.2 t·d-1, or 5-8% of the total SO2 flux(~ 70 t·d-1). Our SO2 explosive dataset data was integrated and inter-compared with infraredradiometer data and very long period (VLP) seismic traces, yielding a complete geophysical-geochemical data corroboration.Finally, we also obtained a very first direct estimate of the puffing contribution to the total SO2budget. It is known that Stromboli's active vents continuously release gas in a stream of gas puffs(emission of gas in discrete packages). After a few tents of meters, puffs cool, decelerate, expand,and finally mingle within the surrounding plume contributed by other vents; therefore, only afew puffs retained their shape long enough to be imaged with UV camera (at least during ourobservations). According to our preliminary data, the SO2 mass contributed by each single puffvaries between 0.14 and 0.45 kg. We thus conclude that puffing may account for 10-20% of thetotal SO2 daily output from Stromboli. Finally, we confirm that passive degassing is likely to be themost significant form of SO2 release at Stromboli (and possibly other open-vent basaltic volcanoes).
|Numero di pagine||1|
|Stato di pubblicazione||Published - 2011|