Volcanic SO2 Emissions During the 2002/2003 Eruption of Stromboli

Stromboli, an island in the Aeolian archipelago northeast of Sicily, Italy is well known for the persistent, frequent and small explosions emitted from its summit craters, a type of activity that is synonymous with the volcano. On December 28th 2002, after several months of higher than usual eruptive activity a partial collapse of the crater structure occurred and lava began to flow from fissures within an old collapse feature on the western flank known as the Sciara del Fuoco (scar of fire). The last major effusive eruption from Stromboli occurred in 1985. Two days later, on 30th December 2002, approximately 7 million m³ of material collapsed from the Sciara into the sea, together with a similar magnitude of material displaced under sea level. This collapse produced a tsunami wave that severely damaged parts of the coast of Stromboli, as well as other islands in the archipelago. Lava effusion continued until July 2003, constituting one of the longest continuous effusive periods in the modern period from this volcano. During most of the effusive period, daily measurements of the SO₂ flux from Stromboli were performed with a COSPEC instrument, from helicopter and from boat. These measurements allow an unprecedented insight into the magma degassing process before, during and after a rare effusive eruption. Typical pre-eruptive fluxes were on the order of 200 tonnes/day of SO₂. Average SO₂ fluxes during the eruption were 500 tonnes/day. Using the original dissolved sulfur content of strombolian magma we calculate the volume of magma required to generate this SO₂ flux, and determine a mass flow rate of approximately 0.5m³/s, comparable with estimates of the lava effusion rate for much of the eruption. We conclude that during the effusive eruption the typical magma circulation with the conduit of stromboli effectively ceased and was replaced by a simple flow with all magma entering the system at depth eventually exiting at the summit. These conclusions allow empirical constraints to be placed on petrological observations of crystal growth processes under both circulation and flow regimes.