Origin of fumarolic fluids emitted from a nonerupting volcano: Radionuclide constrains at Vulcano (Aeolian islands, Italy)

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