Waveform Template Matching and Analysis of Hydroacoustic Events from the April-May 2015 Eruption of Axial Volcano

The submarine emplacement of new lava flows during the 2015 eruption of Axial Volcano generated a series of impulsive acoustic signals that were captured by seismic and hydrophone sensors deployed as part of the Ocean Observatories Initiative cabled array network. A catalog of >37,000 explosions was created using a four-channel waveform matching routine using 800 template arrivals. Most of the explosions are sourced from a set of lava mounds erupted along the volcano's northern rift; however, a subset of 400 explosions are located within the caldera and track the flow of lava from a vent near its eastern rim. The earliest explosion occurs at 08:00 UTC on April 24, approximately four hours after the seismicity rate began to increase and two hours after bottom pressure recorders indicate the caldera floor began to subside. Between April 24 and 28 event rates are sustained at 1000/day. The rate then decreases gradually with explosive activity ending on 21 May, coincident with the initial re-inflation of the caldera. The windowed coefficient of variation of the inter-event time is approximately 1 throughout the eruption, consistent with a random process. The size-frequency distribution shows a bimodal pattern, with the loudest explosions, having received levels up to 157 dB re 1 micro-Pa, being produced during the first few hours of the eruption.