SULFUR OUTPUT AND MAGMA DEGASSING BUDGET OF STROMBOLI VOLCANO

STROMBOLI volcano in the Aeolian islands has been erupting continuousl y for more than 2,000 years(1), and probably as many as 5,000, followi ng a major flank collapse(2,3). Here we describe air-borne measurement s of the plume flux of SO2 during 1980-93, which show that the volcano emits very large amounts of gas, mostly by open-conduit degassing bet ween explosive outbursts, while exuding little basalt. Microprobe anal ysis of sulphur in the K-rich (shoshonitic) basalt, along with data fo r primitive basalts in the region(4,5), suggests that the time-average d SO2 flux is produced by intrusive degassing of 0.01-0.02 km(3) yr(-1 ) of magma, 100-200 times more than the volume erupted. Over 5,000 yea rs, this rate implies that 50-100 km(3) of intruded basalt would have been degassed, suggesting either that the volcanic pile has grown subs tantially by intrusion(6) or, more probably, that a large magma storag e system is emplaced at a shallow level within the crustal basement. O ur results indicate that Etna and Stromboli alone provide 10% of the g lobal budget of volcanic SO2.