Gravity monitoring of Nysiros volcano activity:2001-2003 preliminary results.

Topographic monitoring of gravity benchmarks, based on a differential-mode, dual-frequency GPS, started in 2002 on Nisyros volcano. A monitoring network was installed in June 2001. The sites were selected in parts of the island experiencing different seismic-tectonic processes, in order to detect their relative movements. In June 2002, monitoring with the microgravity network was repeated for the first time. The comparison of the resulting values with those recorded in 2001 showed a maximum variation of +0.034 mGal in the active volcanic area, with an increasing trend towards South. In 2003, the monitoring was repeated. The resulting G variations were comparable to those observed in 2001-2002. However, with the installation of a new station in 2002, the G variations proved to be confined to the most active volcanic areas. The extent of the variations recorded between 2001 and 2003 largely exceeded the measuring errors, suggesting that such variations are to be ascribed to mass variations of the volcanic complex.