HR: 0800h
AN: V21C-0727    [Abstracts]
TI: Magma Vesiculation and Infrasonic Activity in Open Conduit Volcanoes
AU: * Colo', L
EM: livia.col@tiscali.it
AF: Dipartimento Scienze della Terra, Universita' degli studi di Firenze, via La Pira, 4, Firenze, FI 50121, Italy
AU: Baker, D R
EM: donb@eps.mcgill.ca
AF: Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, QC H3A2A7, Canada
AU: Polacci, M
EM: polacci@ct.ingv.it
AF: INGV, sezione di Catania, Piazza Roma, 2, Catania, CT 95123, Italy
AU: Ripepe, M
EM: maurizio.ripepe@unifi.it
AF: Dipartimento Scienze della Terra, Universita' degli studi di Firenze, via La Pira, 4, Firenze, FI 50121, Italy
AB: At persistently active basaltic volcanoes such as Stromboli, Italy degassing of the magma column can occur in "passive" and "active" conditions. Passive degassing is generally understood as a continuous, non explosive release of gas mainly from the open summit vents and subordinately from the conduit's wall or from fumaroles. In passive degassing generally gas is in equilibrium with atmospheric pressure, while in active degassing the gas approaches the surface at overpressurized conditions. During active degassing (or puffing), the magma column is interested by the bursting of small gas bubbles at the magma free surface and, as a consequence, the active degassing process generates infrasonic signals. We postulated, in this study, that the rate and the amplitude of infrasonic activity is somehow linked to the rate and the volume of the overpressured gas bubbles, which are generated in the magma column. Our hypothesis is that infrasound is controlled by the quantities of gas exsolved in the magma column and then, that a relationship between infrasound and the vesiculation process should exist. In order to achieve this goal, infrasonic records and bubble size distributions of scoria samples from normal explosive activity at Stromboli processed via X ray tomography have been compared. We observed that the cumulative distribution for both data sets follow similar power laws, indicating that both processes are controlled by a scale invariant phenomenon. However the power law is not stable but changes in different scoria clasts, reflecting when gas bubble nucleation is predominant over bubbles coalescence and viceversa. The power law also changes for the infrasonic activity from time to time, suggesting that infrasound may be controlled also by a different gas exsolution within the magma column. Changes in power law distributions are the same for infrasound and scoria indicating that they are linked to the same process acting in the magmatic system. We suggest that monitoring infrasound on an active volcano could represent an alternative way to monitor the vesiculation process of an open conduit system.
DE: 4475 Scaling: spatial and temporal (1872, 3270, 4277)
DE: 8400 VOLCANOLOGY
DE: 8428 Explosive volcanism
DE: 8430 Volcanic gases
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting