Geophysical examination of the 27 April 2016 Whakaari/White Island, New Zealand, eruption and its implications for vent physiognomies and eruptive dynamics

Abstract

At approximately 09:36 UTC on 27 April 2016, a phreatic eruption occurred on Whakaari Island (White Island) producing an eruption sequence that contained multiple eruptive pulses determined to have occurred over the first 30 min, with a continuing tremor signal lasting ~ 2 h after the pulsing sequence. To investigate the eruption dynamics, we used a combination of cross-correlation and coherence methods with acoustic data. To estimate locations for the eruptive pulses, seismic data were collected and eruption vent locations were inferred through the use of an amplitude source location method. We also investigated volcanic acoustic-seismic ratios for comparing inferred initiation depths of each pulse. Initial results show vent locations for the eruptive pulses were found to have possibly come from two separate locations only ~ 50 m apart. These results compare favorably with acoustic lag time analysis. After error analysis, eruption sources are shown to conceivably come from a single vent, and differences in vent locations may not be constrained. Both vent location scenarios show that the eruption pulses gradually increase in strength with time, and that pulses 1, 3, 4, and 5 possibly came from a deeper source than pulses 2 and 6. We show herein that the characteristics and locations of volcanic eruptions can be better understood through joint analysis combining data from several data sources.

Phreatic eruption dynamics derived from deposit analysis: a case study from a small, phreatic eruption from Whakāri/White Island, New Zealand

“…To unravel this event, we describe the eruption deposits and the relative timing between the ballistic pulses (derived from the seismoacoustic data) and surge generation. We refine our timeline and impacts with the geophysical monitoring data (Walsh et al 2019) to determine the number of pulses that ejected material beyond the crater area. Finally, we illustrate the emplacement dynamics and implied hazard of phreatic eruptions in the area proximal to the crater lake.…”

“…As the eruption was unwitnessed, the number of eruptive pulses that contributed to the ballistic field could only be determined based on seismic and acoustic signals. White Island hosts two permanent Geonet seismometers with acoustic sensors (Walsh et al 2019) and due to the ongoing higher activity level since 2000, three additional temporary seismometers were on the island at the time of We focussed most of the photogrammetry survey towards the western subcrater, which is periodically infilled by a warm, acidic lake. At the time, there was no lake present and this survey attempted to quantify the topography of the inner crater basin ~ 8 months after the eruption described here.…”

“…The most recent White Island eruption occurred on 27 April 2016, at ~ 10 pm (local time) and because of the timing the eruption was not witnessed by visitors to the island or on the webcams because of low light conditions at the time. It was, however, recorded by a network of portable seismometers, and acoustic sensors that recorded six distinct explosions or pulses of varying energy release (Walsh et al 2019). In the aftermath of this event, we made observational flights within 24 h and ground-based assessments in the subsequent weeks and months and a drone-based Structure-From-Motion (SFM) survey of the crater floor ~ 8 months after the event when the lake had evaporated/drained.…”

“…In the aftermath of this event, we made observational flights within 24 h and ground-based assessments in the subsequent weeks and months and a drone-based Structure-From-Motion (SFM) survey of the crater floor ~ 8 months after the event when the lake had evaporated/drained. Here, we use this eruption and the detailed analysis of the resulting deposits to examine the energetics, volume, and emplacement dynamics of the eruption sequence and tie this to the geophysical (Walsh et al 2019) record. In this way, our companion papers highlight strategies for unravelling the complexity of a multi-phase eruption sequence using disparate analysis tools.…”

Special issue “Towards forecasting phreatic eruptions: examples from Hakone volcano and some global equivalents”

“…This special issue collected intriguing examples from White Island, Kawah Ijen, and Hakone (Yukutake et al 2017Caudron et al 2018;Harada et al 2018;Jolly et al 2018;Walsh et al 2019). Walsh et al (2019) located eruptive pulses emitted during a phreatic eruption that occurred at White Island on 27 April 2018 by a joint analysis combining acoustic and seismic data. The locations of the eruption vent were inferred using an amplitude source location method, and the depth of eruption pulses was inferred from volcanic acoustic-seismic ratios.…”