The 7 September 2008 Vulcanian explosion at Stromboli volcano: Multiparametric characterization of the event and quantification of the ejecta

On 7 September 2008 a major ash explosion occurred from the SW summit crater of Stromboli volcano. This explosive event lasted similar to 2 min and consisted of three discrete eruptive pulses, forming an eruptive ash cloud similar to 500-600 m high and similar to 300 m wide, rising with speed of 20-27 m s(-1). The event was recorded by our camera and seismic networks, as well as by two electric stations installed at a 500 m mean distance from the SW crater. The electric signals recorded by the two stations during this event were 10(6) times greater than signals recorded during the persistent Strombolian activity, and the seismic trace had a bigger amplitude and a longer duration. Camera image analysis allowed us to infer that a partial obstruction took place at the SW crater three days before the explosive event, suggesting that a constriction within the upper conduit could have likely led to magma overpressure. Data analysis, combined with previous experimental investigations, revealed that the higher energy output of the ash explosion, when compared to the persistent Strombolian activity, resulted in a greater magma fragmentation and erupted mass. Integration of the different parameters allowed us to classify the event as a Vulcanian type, and electric signal analysis enabled retrieval of the total volume of erupted ash and of the amounts of the juvenile, phreatomagmatic, and lithic components.