Dynamics of low energy explosive activity at Stromboli volcano (Aeolian Islands, Italy)

Perugia, Italy

Twenty low-energy (0.0077 0.625 kgs-1) explosions from the Northeast Crater of Stromboli Volcano, recorded by a thermal camera, were studied in detail to better understand their dynamics. Each single burst consists of three different jets of different material which come one after another: at first, cold vapour flashes above the crater, expands and then disappears within 0.6 s after the onset of the explosion, at a velocity of 40-113 ms-1. This air shock wave is immediately followed by the expansion of a jet of hot magmatic gas, at a velocity of 35-75 ms-1. Colder coarse tephra (bombs and scoriae) appear about 1.6-2 s after the onset of explosion, moving at a reduced velocity (28-60 ms-1). Further on, some of these data were utilized to calibrate a set of flow simulation in a 220-260-m-long conduit, which validates the model of slug flow for these kinds of eruptions. Finally, coupling all the collected data with the stratigraphy of the volcano, we hypothesized that a physical barrier might be responsible for the formation of slugs of gas and their ascent toward the surface at regular intervals. This barrier acts as a siphon and seems to be generated by the displacement of the upper conduit due to summit instability. This model justifies the ~constant interval between explosions, the insensitivity of this behavior to the occurrence of effusive episodes and highly explosive events, as well as the generation of fairly constant petrochemical characteristics of the magma which is commonly erupted, with time.