Investigating Kīlauea’s 2018 Offshore Lava Emplacement Through Hydroacoustic Data

The 2018 eruption of Kīlauea Volcano produced an unprecedented volume of lava, creating 3.5 km2 of new land on Hawai`i’s Big Island (Soule et al., 2021). Lava expelled from the Ahu`aila`au vent (originally called Fissure 8) traveled ~13 km to where it entered the ocean. Over half of the lava erupted in 2018 was emplaced offshore where it produced four new submarine lava deltas (Soule et al., 2021). In response to the eruption, a network of 12 ocean-bottom seismometers (OBS) with attached hydrophones was deployed on Kīlauea’s submarine south flank. Ten of the instruments successfully recorded data from July 9 through September 16, 2018 and captured the start and end of the Ahalanui ocean entry. This study presents an analysis of offshore lava emplacement during Kīlauea’s 2018 eruption using hydroacoustic data. Short duration (<2 >sec), broadband (20-90 Hz) signals observed in the hydroacoustic record, proposed here as lava-water interactions, were examined using waveform cross-correlation and modeled with the program Bellhop (Porter, 2011) to constrain their location. Real-time Seismic Amplitude Measurement (RSAM) data were used to correlate lava effusion from Ahu`aila`au with times of prominent offshore lava emplacement. The results of this study indicate that intact submarine lava flows produced unique hydroacoustic signals while traveling distances up to 1500 m offshore. Surges in subaerial lava effusion were also found to have continued into the submarine environment, producing increases in hydroacoustic RSAM. Together, the results of this study will serve to help describe Kīlauea’s submarine environment during its 2018 eruption.