Integrated geophysical studies of the hydrothermal system at Nisyros Island, Greece
A microgravity and GPS monitoring network established at the Nisyros caldera volcano (Greece) in 2003 enables the quantification of subsurface processes over time at this restless volcano. Data indicate that the current activity is dominated by mass and density changes at depth, most likely due to dynamic changes in a shallow hydrothermal system. The purpose of the fieldwork in 2007, supported by loan 835, was to survey a network of 20 joint GPS/gravity benchmarks and to obtain continuous multiparametric geophysical data near the hydrothermally active areas of the caldera floor in order to shed light onto sub-surface dynamics. The latter investigations revealed nonsteady short-term oscillatory signals, recorded by both geodetic as well as seismic and electromagnetic instrumentation. The combined records indicate that the oscillations are associated with thermohydromechanical disturbances of the hydrothermal system. The dominant period of oscillation (>60 min) reflects short-term processes most likely associated with instabilities in the degassing process. Re-occupation of the network in 2007 enabled tracking of island-wide changes in the subsurface structure and ectend the observation period to more than 4 years Some of the obtained data in 2007 is also used to construct a Bouguer anomaly map of the island and will provide a crucial starting point for the modelling of gravity/height change and other geophysical data in the future.
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