金曜日セミナー：(2020年3月6日) Dr. Kyle Anderson (USGS)
The 2018 eruption of Kīlauea Volcano: Unprecedented insight into the onset and evolution of a caldera collapse
U.S. Geological Survey
Moffett Field, California, USA
Few caldera collapses have been recorded in modern times. The 2018 eruption of Kīlauea resulted in the largest summit collapse at the volcano in more than two centuries and yielded unprecedented observations of the onset and evolution of a collapsing caldera. Activity was observed in detail using radar satellites, GNSS receivers, borehole tiltmeters, gravimeters, seismometers, optical and thermal cameras, and unoccupied aerial vehicles (UAVs), which produced rich multiparametric datasets. Collapse proceeded over more than two months as a series of 62 discrete meters-scale events which ultimately produced a caldera of ~0.8 cubic kilometers. Each collapse event produced upwards-and-outwards ground deformation around the caldera (as at Miyakejima in 2000), and many collapses were followed by deformation transients and surges in effusion rate on Kīlauea’s East Rift Zone tens of kilometers from the summit. Critically, the days preceding the onset of caldera collapse included the draining of an active lava lake, which permits an estimate of the rate of pressure change in the sub-caldera magma reservoir. I will summarize the 2018 eruption of Kīlauea and discuss the use of a simple magma reservoir model together with joint Bayesian analysis of a variety of data sets to estimate the location and geometry of shallow magma storage, properties of magma within the reservoir, the conditions that led to the onset of collapse, and the fraction of magma remaining in the reservoir at the end of the eruption. These results suggest that the caldera began to collapse after withdrawal of only a small fraction of its stored magma, and that the eruption ended before evacuation was complete. I will also briefly discuss ongoing lines of investigation, including the mechanism of ground deformation observed during collapse events.