LAUSR

In December 2016, the unmonitored Bogoslof volcano unexpectedly began erupting, producing at least 70 explosions over the next 8.5 months. Roughly half of the explosions were preceded by observable short-term precursory activity, defined here as seismic activity ending within 30 min of the explosion onset or an earthquake swarm ending within a few hours before the explosion onset. Five different types of precursors were noted during the Bogoslof eruption: non-swarm earthquakes, earthquake swarms, rapid rate events, tremor, and chromatic tremor. Most of the precursors that were detectable by the nearby seismic networks (> 45 km away) occurred during the first 3 months of the eruption, with nearly all precursory earthquake swarms occurring during this period. A hydrophone deployed ~ 7 km northeast of the summit for the last 3 months of the eruption detected weaker activity that was not recorded by the more distant seismic networks. We describe the observed precursors and discuss their inter-relations. Overall, the precursors seem indicative of processes occurring throughout the volcanic system and suggest possible changes in the system during the eruption. We then compare the short-term precursors with explosion parameters, such as plume height, duration, and occurrence of lightning, to look for relations that may provide more insight into the eruption dynamics and subsurface processes and help to further improve forecasting. We find no obvious relations between any of the precursor or explosion parameters, suggesting that their use in forecasting eruption characteristics at Bogoslof is limited.