Waveform analysis of seismoacoustic signals radiated during the fall 1996 eruption of Pavlof Volcano, Alaska

Theoretical modeling of acoustic and seismic signals associated with the 1996 strombolian eruption of Pavlof volcano suggests that volcanic tremor at Pavlof originates in the deeper part of the magma conduit, and is generated by random fluid oscillations in the magma flow. Explosions are believed to occur in the shallower part of the magma conduit, and to be caused by the rapid and violent expansion of metastable magma‐gas mixtures. The effect of increasing the exsolved quantities of H 2 O and CO 2 gas with reduced pressure in the melt is to decrease the sound speed and density of the magma‐gas mixture. This causes an acoustic decoupling of the upper and lower parts of the magma conduit. The reduced sound speed and density of the melt at shallow depths present a sharp impedance contrast, which strongly reflects acoustic energy originating at depth and traps it in the lower part of the magma conduit. Alternatively, acoustic energy originating from the upper part of the conduit remains trapped in the low‐velocity region formed by the exsolved gas in the melt, and hence shallow explosions may preferentially couple into the atmosphere. Explosion signals may be triggered by an increased flow of melt at depth, and may be preceded and accompanied by vigorous mass flux transients.