Upper conduit structure and explosion dynamics at Stromboli

Abstract

Modeling of very long period seismic data recorded during explosive activity at Stromboli in 1997 provides an image of the uppermost 1 km of its volcanic plumbing system. Two distinct dike-like conduit structures are identified, each representative of explosive eruptions from two different vents located near the northern and southern perimeters of the summit crater. Inferred volumetric changes in the dikes are viewed as the result of a piston-like action of the magma associated with the disruption of a gas slug transiting through discontinuities in the dike apertures. Accompanying these volumetric source components are single vertical forces resulting from an exchange of linear momentum between the source and the Earth. In the dike system underlying the northern vent, a primary disruption site is inferred at an elevation near 440 m where a bifurcation in the conduit occurs. At a depth of 80 m below sea level (bsl), a sharp corner in the conduit marks another location where the elastic response of the solid to the action of the upper source induces pressure and momentum changes in the magma. In the conduit underlying the southern vent, the junction of two inclined dikes with a subvertical dike at 520 m of elevation is a primary site of gas slug disruption, and another conduit corner 280 m bsl represents a coupling location between the elastic response of the solid and fluid motion.