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High-Frame Rate Thermal Imagery of Strombolian Explosions: Implications for Explosive and Infrasonic Source Dynamics
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Looking into stromboli conduit with a multi-parametric eye
No full textShort 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
MISURE DI RADIAZIONE INFRAROSSA ASSOCIATA AI SEGNALI SISMICI ED INFRASONICI PRODOTTI DALL'ATTIVITÀ ESPLOSIVA DELLO STROMBOLI
No full textCharacterization of the gas–magmatic outflow at a volcanic vent through integral–equation based inverse acoustics
No full textAir-wave phases in strombolian explosion quake seismograms: a possible indicator for the magma level?
No full textMany explosion-quake seismograms recorded near the active craters at Stromboli are dominated by two distinct onsets: a first low-frequency phase and a second high-frequency one. Particle-motion diagrams show a P-wave characteristic for the low-frequency phase, whereas in the high-frequency onset the longitudinal polarization is lost and the pattern becomes chaotic in the horizontal as well as in the vertical plane. The air-pressure pulse generated by the volcanic explosion is detected by the seismometer as a high-frequency signal, and we assume as source mechanism an explosion at the top of the magma column, generated by rising gas bubbles. The different path lengths and velocities for the seismic wave and the air-wave are the reasons for the difference in arrival times Dt between the low-frequency and the high-frequency onset. We tried to deduce the magma level and gas velocity in the conduit, from observed Dt values. If the pressure pulse inside the consuit is assumed yo be lower (30-70 m/s) than the sound speed, the magma level remains reasonably stable, even for large changes of Dt.Published201-2065V. Sorveglianza vulcanica ed emergenzeN/A or not JCRrestricte
Air-wave phases in strombolian explosion quake seismograms: a possible indicator for the magma level?
No full textMany explosion-quake seismograms recorded near the active craters at Stromboli are dominated by two distinct onsets: a first low-frequency phase and a second high-frequency one. Particle-motion diagrams show a P-wave characteristic for the low-frequency phase, whereas in the high-frequency onset the longitudinal polarization is lost and the pattern becomes chaotic in the horizontal as well as in the vertical plane. The air-pressure pulse generated by the volcanic explosion is detected by the seismometer as a high-frequency signal, and we assume as source mechanism an explosion at the top of the magma column, generated by rising gas bubbles. The different path lengths and velocities for the seismic wave and the air-wave are the reasons for the difference in arrival times Dt between the low-frequency and the high-frequency onset. We tried to deduce the magma level and gas velocity in the conduit, from observed Dt values. If the pressure pulse inside the consuit is assumed yo be lower (30-70 m/s) than the sound speed, the magma level remains reasonably stable, even for large changes of Dt.Published201-2065V. Sorveglianza vulcanica ed emergenzeN/A or not JCRrestricte
STP: What about dynamics?
No full textThe origin of volcanic tremor is still the subject of vigorous scientific debate. One of the most recent models, by Ripepe and Gordeev, suggests that volcanic tremor is related to the coalescence of bigger gas bubbles from a layer of smaller ones in the magma foam, forced by a structural barrier. The evidence of this model is mainly related to the relationship between the seismic signal and infrasonic waves. These must be generated by the same dynamical process, although the latter are related to a successive phase, i.e. the bursting of the bubbles at the magma-air interface.
Previous studies by Carniel and Di Cecca furnished evidence that volcanic tremor can be considered as a state variable of a deterministic dynamical system of "low" dimension. If the pressure signal is related to the same dynamical process, the two time series should not show too different dynamical behaviour.
On 19 June 1999, an experiment was carried out, recording simultaneously not only seismic and pressure waves, but also thermal data, using a Minolta/Land Cyclops 330 infrared thermometer aimed at one of the vents in NE Crater. Preliminary results from the dynamical analysis of the resulting time series are presented and discussed
Interaction of seismic and airwaves recorded at Stromboli volcano
No full textExplosion-quake seismograms recorded at Stromboli show that seismic phases with a high-amplitude and high-frequency content propagate with a velocity of approximately 330 m/s - the sound speed. The analysis of seismograms, recorded at a distance of 500 m from one of the three active vents, shows for the first onset a low frequency and particle motion characteristics of a p-wave, which loses its longitudinal polarization with the onset of the air-wave.
Recording the explosion-quake simultaneously with a microphonewe would ascertain that the high frequency onset coincides with the air-wave's. In order to better understand the seismic wavefield generated by the atmospheric pressure, we performed a controlled source experiment at Stromboli using a seismic gun. Seismograms with the same two phases and particle motions comparable with the volcanic seismic data were obtained. A second experiment demonstrated, that the air-wave propagates at least in the uppermost 1m of the gound. We suggest that the seismic source of the corresponding seismograms is an explosion at the top of the magma column and conclude that the p- and air-waves are both generated in the same point and at the same time.Published65-681.4. TTC - Sorveglianza sismologica delle aree vulcaniche attiveJCR Journalreserve
Spectroscopic capture of 1 Hz volcanic SO2 fluxes and integration with volcano geophysical data
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