HR: 08:35h
AN: V51F-03 INVITED    [Abstracts]
TI: The role of magma degassing on bradyseismic crises at Campi Flegrei inferred from the monitoring of the hydrothermal activity. Possible inferences on Yellowstone
AU: * Chiodini, G
EM: chiod@ov.ingv.it
AF: INGV, OV, via Diocleziano, 328, Napoli, 80124, Italy
AB: The detailed processing of long time series of fumarolic compositions, available at Solfatara (Campi Flegrei) since 1983, carries a double thermobarometric signature. Temperatures of about 360°C, i.e. close to the critical point of water, are inferred by methane chemical-isotopic geoindicators, by gas equilibria in the H2O-CO2-CH4 gas system and by the H2/Ar geothermometer. These high temperatures are representative of a deep zone where magmatic gases flash hydrothermal liquid forming a gas plume where the kinetically fast reactive species (H2 and CO) re-equilibrate at temperatures of 200-240°C. The stable isotope compositions of H2O and CO2 shows that sampled effluents are mixture between magmatic fluids and the vapor generated by the vaporization of hydrothermal liquids of meteoric origin. A typical ‘andesitic' water composition has been inferred for the magmatic component, similar to that emitted by other volcanoes of the Mediterranean area. This mixing model suggests that bradyseismic crises, periodically affecting Campi Flegrei, are triggered by pulsing injections of CO2-rich magmatic fluids at the bottom of the hydrothermal system. A strong increase of the fraction of the magmatic component marked the bradyseismic crisis of 1982-84 and four minor episodes of ground uplift and seismicity occurred in 1989, 1994 and 2000 and 2006. The successful application of physical-numerical simulations asses the physical feasibility of the proposed conceptual model. Ground deformations, gravitational anomalies and seismic crisis can be well explained by the complex fluid dynamic processes caused by magma degassing events. Data on the fumaroles of other volcanoes suggest that magma degassing events frequently occur in dormant volcanoes causing crisis periods not necessarily linked to magma movement but rather to pulsating degassing processes from deep pressurized, possibly stationary, magma bodies. We can hypothesize that similar processes occur at Yellowstone that is characterized by the presence of a huge hydrothermal system and by the periodical occurrence of volcanic unrests episodes. Finally, resolving magmatic vs. hydrothermal fluid components needs for a better comprehension of the processes which occur at dormant volcanoes before an eruption.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 8419 Volcano monitoring (7280)
DE: 8430 Volcanic gases
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting