Short period seismic data have represented for a long time the major geophysical dataset available for the investigation of the processes going on inside a volcano with moderate permanent explosive activity such as Stromboli (Aeolian Islands, Italy). The installation of (arrays of) broadband seismic instruments has considerably widened our views but in order to go further with the understanding and with the modelling, the integration of seismic data with other signals is a strong necessity.
A path-finder experiment was conducted in June 1999 recording simultaneous thermal, seismic and infrasonic measurements, and a more extensive field campaign was carried out in May 2000. The role of the gas has always been recognized as a major one in the dynamics of the conduit.
Analyses of data recorded in 1999 campaign indicate that periods of high and low rates of explosive activity can be related to the magnitude and frequency at which small gas bursts occur. These in turn can reflect the dynamics of the build-up and decay of foam layers and, possibly, offer an insight into the rate at which fresh, gas-rich magma supplies the shallow vents system. Variations in gas temperature, recurrence of gas bursts, and frequency of strombolian explosions indicate that magma-foam levels, or magma-gas supply, could change over minute-long periods as the system cycles between 5- to 40-minutes long periods characterized by different degassing rates.
These first results are being verified and extended by analyzing the longer datasets recorded in May 2000 campaign. In our model, foam layer generation and collapse at Stromboli's shallow system alternates between periods of low and high activity, which may be linked to the rise, and subsequent degassing and sinking, of discrete fresh magma/gas batches. This model seems to be confirmed by the good correlation between time delays between infrasonic and infrared onsets and temperature fluctuations at the vent.
