HR: 0830h
AN: V51F-0339    [PDF]
TI: Multi-parameters Analysis Tracks Changes From the Effusive to The Explosive Behaviour of Volcanic Activity at Stromboli.
AU: * Marchetti, E
EM: marchetti@geo.unifi.it
AF: universita' di Firenze, via G. Lapira, 4, FIRENZE, 50121 Italy
AU: Ripepe, M
EM: mripepe@geo.unifi.it
AF: universita' di Firenze, via G. Lapira, 4, FIRENZE, 50121 Italy
AU: Harris, A J
EM: harris@higp.hawaii.edu
AF: University of Hawaii, Correa Road, Honolulu, 96822 United States
AU: Fiaschi, A
EM: fiaschi@igt.it
AF: universita' di Firenze, via G. Lapira, 4, FIRENZE, 50121 Italy
AU: Ulivieri, G
EM: gulivieri@geo.unifi.it
AF: universita' di Firenze, via G. Lapira, 4, FIRENZE, 50121 Italy
AB: The Dec. 2002 eruption of Stromboli volcano was followed by almost six months of lava flow characterized by several effusive vents active in the Sciara del Fuoco, at an elevation of 650 m and by the absence of explosive activity at the summit craters. At the end of May 2003, the effusion rate decreased leading to a transition from the effusive to the explosive activity. This transition was a long and smooth process, which took place over a period of 2-3 months, and it was nicely evidenced by continuos seismic, infrasonic and thermal data. We monitored seismic, infrasonic and thermal amplitude and the time delays between their onset recorded at a station deployed at an elevation of 750 m and a distance of 500 m from the active craters. This station was provided with a CMG-40T Guralp broadband seismometer, a pre-amplified Monacor condenser microphone sensitive 46 mV/Pa in the 1-20 Hz infrasonic band, and a 15 degree FOV OMEGA infrared thermometer with a sensitivity of 1 mV/C, in the range between -40 and 1100 C. The Position of the radiometer allows to detect emissions of hot gas and material from both NE and SW craters. The transition from effusive to explosive behaviour is associated with a general increase in the amplitude of the seismic VLP, infrasonic pressure and thermal variation and with a decrease in the delay times calculated for the seismic, infrasonic and thermal onset. Thermal amplitude is proportional to the temperature and the quantity of the hot material covering the instruments FOV and is then representative of the size of the explosions. Amplitude of the infrasound is related to the gas overpressure while amplitude of the VLP is most likely due to the volume changes induced by gas expansion in the magma. Monitoring the seismic, acoustic and thermal amplitude is then equivalent to monitor the degree of gas exsolved in the system. Moreover, the time delays between these 3 parameters depend on several factors like gas jet velocity, and position of the magma level in the conduit. Therefore, amplitudes and delay times are somehow representative of the explosivity level of the system. We show that the decrease in the effusion rate was followed by the gradual increase of the seismic, acoustic and thermal amplitude and by a sensitive reduction in the time delays suggesting the progressive uprise of the magma level in the conduit.
DE: 7280 Volcano seismology (8419)
DE: 8400 VOLCANOLOGY
DE: 8414 Eruption mechanisms
DE: 8419 Eruption monitoring (7280)
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting