Source Mechanism of Caldera Collapse Events During the 2018 Kīlauea Volcano Eruption

Date: 4/26/2019

Time: 06:00 PM

Room: Fifth Avenue

The 2018 eruption of Kīlauea Volcano produced voluminous lava flows from the Lower East Rift Zone that were accompanied by continuous deflation at the summit of the volcano. Sixty-two semi-regular collapse events at the summit caldera resulted in about 4 km² of the caldera dropping between 100-400 m. Total volume loss at the summit over the 3-month-long eruption estimated by differencing pre- to post-eruption digital elevation models was ~825x10⁶ m³. Previous studies of very-long-period (VLP) seismicity at Kīlauea have illuminated the shallow magmatic transport system as a composite of near-vertical dikes featuring an east striking dike intersecting a north striking dike near the northeast corner of the Halema`uma`u pit crater. VLP seismicity from a source centroid positioned on this intersection near sea level has been observed since the deployment of broadband sensors in 1994. The dominant component of motion for each of the collapse events as observed on the horizontal components of the local broadband seismometers is a simple step in ground displacement. Geodetic observations indicate this signal is originating in ground tilt. Waveform inversion of the raw seismic data with Green’s functions convolved with both displacement and tilt responses of the broadband instruments illustrates a source mechanism consisting of rapid inflation of the underlying dike system over of period of 5-10 s that overprints the continuous deflation of the dike system. This behavior is similar in character to that observed in previous years when piecemeal collapses of wall rock impacted the lava lake in the Overlook pit crater. Using a simple lumped parameter model of the magmatic system, the mass of each collapse event associated with the inflationary step is estimated to be ~1.6x10⁶ m³ for the first 12 events and ~16 x10⁶ m³ for the remaining 50 events. The sum of all collapse events is ~824x10⁶ m³ suggesting a remarkable conservation of mass between the draining of the summit magmatic system and associated collapse events.

Presenting Author: Phillip Dawson

Authors