Relative partitioning of acoustic and seismic energy during Strombolian eruptions

The relative elastic energy partitioning during Strombolian eruptions can be estimated from acoustic pressure and seismic velocity records. We outline methods for determining acoustic and seismic energies for sensors deployed within several kilometers of erupting vents. We use these energies to introduce the concept of the volcano acoustic–seismic ratio (η, or VASR), which is the ratio of elastic energy propagated through the atmosphere and into the earth. Eruption VASR is a physical diagnostic of explosive degassing that is appropriate for comparing eruption mechanisms at individual and between various volcanoes. Here we assess acoustic and seismic energies and corresponding VASR for discrete Strombolian explosive events at Karymsky and Erebus Volcanoes. We attribute the relatively high and stable VASR at Erebus (η = 8, standard deviation 41%) to repeatable source conditions occurring at the surface of a persistent lava lake, with accompanying strong coupling to the atmosphere. Lower and more variable VASR at Karymsky (η = 0.18 in 1998 to η = 1.51 in 1991, with standard deviations of 93% and 313%, respectively) is attributed to changing conditions within a narrow, partially choked conduit. Variable seismo-acoustic energy partitioning for Karymsky, as manifested by the large VASR standard deviation, suggests that conduit conditions affecting VASR, which include magma properties, conduit obstruction, or fragmentation depths can evolve both during the course of an explosion and between successive events.