HR: 0800h
AN: V41A-0400    [Abstracts]
TI: STRUCTURAL CONTROLS ON THE HYDROTHERMAL SYSTEM OF VILLARRICA: EVIDENCE FROM SELF-POTENTIAL MEASUREMENTS
AU: * Hill, G J
EM: graham.hill@sci.monash.edu.au
AF: Australian Crustal Research Centre, Monash University, Building 28, Monash University, Melbourne, VIC 3800, Australia
AU: Cas, R A
AF: Australian Crustal Research Centre, Monash University, Building 28, Monash University, Melbourne, VIC 3800, Australia
AU: Cull, J P
AF: Australian Crustal Research Centre, Monash University, Building 28, Monash University, Melbourne, VIC 3800, Australia
AU: Burgess, M K
AF: San Diego State University, 5500 Campanile Drive, San Diego, Ca 92182, United States
AU: Carter, A J
AF: University of Pittsburgh, University of Pittsburgh, Pittsburgh, Pa 15260, United States
AU: Acuna-Munoz, J
AF: Servico Nacíonal de Geologia y Mineria, Cerro Ņielol s/n, Temuco, 314, Chile
AB: Geological studies at Volcan Villarrica have investigated the volcanic history of this part of the Andes southern volcanic zone but have revealed little information about the hydrothermal and magmatic circulation system. Hydrothermal circulation, and the extent over which it is active on volcanoes, has connotations to hazard mitigation as areas within the hydrothermal cell are often less competent and more prone to failure. A self- potential survey was conducted over a period of three months on two sub-parallel transects from the summit of the volcano. Initial results suggest fluid circulation is occurring. The survey detected a strong amplitude dipolar anomaly reaching a value of -2.7 volt, the minimum in the self potential data indicating the transitional zone from a hydrothermal to hydrological regime of fluid circulation. This anomaly is believed to be a result of a combination of rapid fluid disruption, electro-kinetic, and thermoelectric effects within and surrounding the magmatic conduit system. Heat supplied from the active lava lake and its supply system is the likely driving mechanism for the shallow hydrothermal cell. The location of the dipolar anomaly is coincident with relict caldera from Villarrica II, upon which the modern day Volcan Villarrica is formed. The collocation of the self potential anomaly and the relict caldera suggest that this structural feature acts as a boundary for the hydrothermal cell. The temporal stability of the self potential signal, coupled with the low surface recharge of the system indicates that the hydrothermal system is maintained by water vapour being exsolved from the degassing magma, with only a minor and short lived perturbation resulting form the infiltration of surface waters. The seasonal stability of the self potential field, coupled with stability of the field to infiltration of meteoric waters suggests that any perturbations to the self potential field that are a result of precipitation are short lived. Thus self potential provides a low cost and relatively simple volcanic monitoring tool.
DE: 8400 VOLCANOLOGY
DE: 8419 Volcano monitoring (7280)
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting