ORIGIN OF FUMAROLIC FLUIDS EMITTED FROM A NONERUPTING VOLCANO - RADIONUCLIDE CONSTRAINTS AT VULCANO (AEOLIAN-ISLANDS, ITALY)

The behaviour of Po-210 and Rn-222 in hot fumaroles on the crater rim at Vulcano Island was studied over 12 years (1980-1992) in order to in fer the origin of the fluids. The decreasing activity of Rn-222 observ ed since 1985 results from the mixing of the magmatic component with s hallow water. A part of Rn-222 in the gases is emitted by the surround ing rocks and carried along by the shallow water. Po-210 is completely volatilized at T > 450-degrees-C. Above this temperature its activity remains unchanged with increasing temperature. Po-210 has two differe nt origins: one is magmatic, correlated with Rn-222; the other one is produced by the sublimates deposited in the volcanic edifice. From the magmatic Po-210 component, the volume of degassing magma is estimated to be about either 170,000 m3 or 90,000 m3/day, according to the mode l utilized. In the first case, the associated degassing time is about twelve days.