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In this paper the installation and operation of a system for continuous monitoring of fumarolic gases are described. Several physicochemical and gas parameters such as the concentration of CO2, H2S and Rn in the fumarolic emissions, as well as the temperature of the fumarolic gas and its pressure are measured in intervals of seconds and transferred to a remote station by digital telemetry. Variations in the monitored parameters which were observed during a short flurry of seismic activity in close vicinity to Nisyros are also reported. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

During January 2003 a geophysical study was undertaken on Nisyros volcanic island in order to investigate the formation of a 600 m long superficial fracture. The fracture is distinguished by a main branch of an approximately N-S direction and smaller side branches of E-W, NE-SW and NW-SE directions. The phenomenon was initiated during November 2001 within the caldera of the island and is still active with the fracture gradually extending southwest, towards Stefanos hydrothermal crater. The study comprised electrical resistivity measurements with the direct current (DC) method along two parallel profiles of E-W direction, close to the north and south ends of the fracture, respectively. Each profile included 4 Half-Schlumberger soundings with a maximum AB/2 of 130 m. The field measurements were carried out with ATLAS 350, a DC resistivity meter designed and developed by the authors of this paper. The collected data are proved to be of very good quality and similar to those of previous DC resistivity surveys in the same area. The data processing resulted in electrical models, which are characterized by rather low resistivities (5-400 ohm-m) and delineate lateral electrical discontinuities at depths greater than 10 m. The latter could be attributed to fractured zones, which do not have any superficial manifestations. The derived electrical models are compatible with the local geology and support the idea that the formation of the fracture is directly related with subsidence phenomena within the top 100 m depths. [ABSTRACT FROM AUTHOR]