Abstract
A climactic eruption phase on December 22, 2018, triggered the collapse of the southwest flank and summit of Anak Krakatau stratovolcano, generating a tsunami which struck the coastlines of Sumatra and Java. We employ a selection of remote moored hydroacoustic (H08S, 3307 km; H01W, 3720 km) and infrasonic (IS06, 1156 km; IS07, 3475 km; IS52, 3638 km) stations of the International Monitoring System (IMS) to investigate eruptive activity preceding, during, and after the climactic eruption phase. We observe 6 months of co-eruptive intermittent infrasound at IS06 and powerful infrasound from the climactic eruption on IS06 and IS52. The climactic eruption phase was not detected hydroacoustically, but we observe a ~ 12-day swarm of hydroacoustic signals beginning 24 days before the flank collapse event that we attribute to sustained submarine eruptive activity at Anak Krakatau. We perform hydroacoustic waveform and envelope multiplet analysis to assess event similarity during the hydroacoustic swarm. Hydroacoustic waveforms are not well-correlated, but envelopes with a main pulse duration of ~ 20-s are correlated, with 88.7% of 247 events grouping into two multiplets using a threshold correlation coefficient of 0.75. The repetitive envelopes indicate a repetitive impulsive volcanic process, either underwater submarine explosions or volcanic earthquakes in the solid Earth coupled to the water column from the Sunda Shelf. This study further underscores the potential of remote acoustic technology for detecting and characterizing eruptions at submarine or partially submerged volcanoes.
Highlights
Anak Krakatau (Child of Krakatau) is a highly active basaltic to dacitic stratovolcano located on the rim of the caldera formed by the 1883 paroxysmal eruption of Krakatau in the Sunda Strait of Indonesia (Fig. 1; Camus et al 1987; Stehn 1929)
The hydroacoustic PMCC detections at H08S do not show continuous detections from the direction of Anak Krakatau during the main eruption sequence, possibly due to low signal-to-noise ratio (SNR) caused by interference from a marine seismic survey (Rose 2020)
Due to their consistent back-azimuth range over the 6-month period and temporal coincidence with reports of seismic events, eruption plumes, lava flows, or thermal anomalies at the volcano, we attribute these pulses to periods of subaerial explosive eruption activity at Anak Krakatau
Summary
Anak Krakatau (Child of Krakatau) is a highly active basaltic to dacitic stratovolcano located on the rim of the caldera formed by the 1883 paroxysmal eruption of Krakatau in the Sunda Strait of Indonesia (Fig. 1; Camus et al 1987; Stehn 1929). Anak Krakatau is a partially submerged volcano, defined here as a volcano which rises from the seafloor, with some part of the upper volcanic edifice that has emerged above the sea surface as an island.
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