Report from individual Research Units: INGV-DPC Project V3_5 – Vulcano

Abstract

Four new stations for heat flux monitoring out of main fumaroles field have been installed at the top of La Fossa cone (MN, MS, BN and BS) within June and July 2005, supplying time series of temperatures and self potential recorded hourly. Another station, already operating since 2004 at the base of La Fossa cone, has been considered “the cold reference” to interpret the variations of heat flux recorded at the top. In accordance to the conduction rate equation (Fourier Law), the linear gradients of temperature are a function of the heat flux towards the surface, and this last can be evaluated with a simplified equation. The main time-variation recorded during three years of experimental acquisitions, have been related to the changes in the hydrothermal heat release. They revealed periods of anomalous release of deep fluids (increases in temperature also in the high temperature fumaroles, correlated to increases in the output of steam and carbon dioxide). The new monitoring stations are away from fumarole fields and the measurable surface flows are related to heat transfer from lower layers and to diffuse degassing. Thus, a comparison between gas flux and heat release gives an indication of the different quotes of surface energy release. This experience suggests that the areas showing higher thermal gradient correspond to areas with the highest diffuse CO2 flux. This evidence resulted by the CO2 flux measurements, performed by chamber accumulation method in the monitoring stations and in the surroundings. Moreover the heat flux values obtained from temperature gradient and those recalculated from CO2 flux are similar, indicating that locally both parameters (soil temperature and gas emission rates) reflect the same form of energy release. The comparative analysis of different time-series supplies information related to perturbations of the state variables, useful to verify conceptual framework and to better define “classical” and “new” monitoring techniques for volcanic, as well as seismic surveillanceThree anomalous periods were observed from November 2004, either in the seismic release and in the surface heat flow. So far, the new monitored sites out of the fumaroles area, resulted very sensitive to minor perturbations of the system. However the test of the self potential continuous monitoring device installed in the unsaturated soil, still needs other accurate laboratory test, in order to define the relationship between this geophysical parameter and the geochemical ones (heat release and diffusive fluxes of carbon dioxide).