Temporal changes in inflation sources during the 2015 unrest and eruption of Hakone volcano, Japan

Abstract

Global navigation satellite system data from Hakone volcano, central Japan, together with GEONET data from the Geospatial Information Authority of Japan, were used to investigate the processes associated with the volcanic activity in 2015, which culminated in a small phreatic eruption in late June 2015. Three deep and shallow sources, namely spherical, open crack, and sill, were employed to elucidate the volcanic processes using the observed GNSS displacements, and the MaGCAP-V software was used to estimate the volumetric changes of these sources. Our detailed analysis shows that a deep inflation source at 6.5 km below sea level started to inflate in late March 2015 at a rate of ~ 9.3 × 10 4 m 3 /day until mid-June. The inflation rate then slowed to ~ 2.1 × 10 4 m 3 /day and ceased at the end of August 2015. A shallow open crack at 0.8 km above sea level started to inflate in May 2015 at a rate of 1.7 × 10 3 m 3 / day. There was no significant volumetric change in the shallow sill source during the volcanic unrest, which is evident from interferometric synthetic aperture radar analysis. The inflation of the deep source continued even after the eruption without a significant slowdown in inflation rate. The inflation stopped in August 2015, approximately 1 month after the eruption ceased. This observation implies that the transportation of magmatic fluid to a deep inflation source (6.5 km) triggered the 2015 unrest. The magmatic fluid may have then migrated from the deep source to the shallow open crack. The phreatic eruption was then caused by the formation of a crack that extended to the surface. However, steam emissions from the vent area during and after the eruption were apparently insufficient to mitigate the internal pressure of the shallow open crack. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Source constraints for the 2015 phreatic eruption of Hakone volcano, Japan, based on geological analysis and resistivity structure

“…Hereafter, we called the inflation source a very shallow source (VSS). Inflations of the magma chamber and a hydrothermal system were also inferred after a detailed analysis of the Global Navigation Satellite System data (Harada et al 2018). The seismic activity achieved a climax in mid-May and began to decrease; however, inflations of the VSS, magma chamber, and hydrothermal system continued without any rate changes (Doke et al 2018;Harada et al 2018).…”

“…The eruption continued until the morning of July 1, when the largest tremor activity was observed (Yukutake et al 2017). After the eruption, the inflation of the VSS ceased; however, inflations of the hydrothermal system and magma chamber continued without a significant rate change until the end of August (Doke et al 2018;Harada et al 2018). Steaming from the newly formed crater and fumaroles has continued to the present.…”

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

“…In addition, the interpretation and timing of seismic and acoustic events in the sequence of the eruption can help constrain eruption process. 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.…”

“…Since the opening of the crack is small (< 10 cm), it is highly unlikely that magma (as opposed to hydrothermal fluids) filled the crack. Harada et al (2018) monitored the rate of inflation of Hakone volcano using GNSS, beginning when precursory unrest started approximately 3 months before the 2015 eruption, and modeled the inflation sources. The deep source at 6.5 km BSL, which is interpreted as a magma chamber, first started inflating at the end of March, then the shallow open crack at approximately 800 m ASL started inflating in mid-May.…”

Volcanic Unrest at Hakone Volcano after the 2015 phreatic eruption — Reactivation of a Ruptured Hydrothermal System?

“…The 2001 unrest accompanied an earthquake swarm, and deep and shallow in ation as observed by Global Navigation Satellite System (GNSS) and a tiltmeter network, and culminated with a blowout of a steam production well (SPW) in Owakudani (500 m deep). Since the 2001 unrest, major volcanic unrest episodes comprising earthquake swarms, deep in ation detected by a GNSS network, and deep low frequency events (DLF) were observed in 2006, 2008-2009and 2013(Harada et al 2018Yukutake et al 2019). In terms of seismicity, these events can be intensive as historical unrest episodes before 1960.…”