Monitoring ground deformation of eruption center by ground-based interferometric synthetic aperture radar (GB-InSAR): a case study during the 2015 phreatic eruption of Hakone volcano

Abstract

We successfully monitored the ground deformation of an eruption center during the 2015 phreatic eruption of Hakone volcano, Japan, using ground-based interferometric synthetic aperture radar (GB-InSAR). GB-InSAR has been developed and applied over the past two decades and enables the frequent (< 10 min) aerial monitoring of surficial deformation of structures and slopes. We installed a GB-InSAR 4 days before the eruption of Hakone volcano on June 29, 2015, and monitored the ground deformation of an area where uplift was detected by a satellite InSAR. The ground deformation observed by the GB-InSAR began suddenly on the morning of June 29 almost coincident with the intrusion of hydrothermal fluid that was inferred by other geophysical observations. The hydrothermal crack is considered to have caused the eruption, which was known by an ash fall 5 h later. The GB-InSAR results indicated a significant uplifted area which is approximately 100 m in diameter, and new craters and fumaroles were created by the eruption in and around the area. The displacement reached up to a total of 45 mm until the evening of June 29 and continued at least until the morning of July 1. During our observation, the displacement rate decreased twice, and the timing of each decrease seemed to correspond to the formation of new conduits as implied from geophysical observations.

Ground-Based Radar Interferometry: A Bibliographic Review

“…In particular, Stromboli volcano, Italy, (see Figure 10d) is one of the most studied volcanoes in the world [77][78][79][80][81] and it has been continuously monitored by terrestrial radar since 2008 [26]. Also, Soufrière Hills in the Montserrat island [82] and Hakone volcano in Japan [83] have been monitored by terrestrial radar.…”

“…The main finding is that this technique is effective even by a terrestrial radar, but its accuracy is sensibly worse than traditional equipment (photogrammetry or Terrestrial Laser Scanner) [10]. [83] have been monitored by terrestrial radar.…”

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

“…At virtually the same time as the crack formed, the beginning of a local uplift around SPW52 was observed by a ground-based InSAR, and pressurization immediately beneath the steaming area was indicated (Kuraoka et al 2018). Because the visibility was poor on the day of the eruption, the timing of the onset of the eruption remains ambiguous; however, the beginning of gas emissions at 7:32, a mudflow or debris flow at approximately 11:00, and ash fall at approximately 12:30 were assumed from different observations (Mannen et al 2018b;Yukutake et al 2018).…”

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

“…InSAR (Interferometric Synthetic-Aperture Radar) presently plays a key role in volcano monitoring. During the 2015 Hakone eruption and unrest, InSAR data were critically important for planning mitigation measures ) and has to date resulted in three prominent literature contributions related to InSAR, two in this special issue Kuraoka et al 2018) and one in another journal (Kobayashi et al 2018). Doke et al (2018) detected the open crack that was formed by the 2015 eruption by analysis of ground deformation observed by satellite InSAR.…”

“…The pre-eruptive pressurization of the hydrothermal system of the volcano was also detected as local uplift by the InSAR analysis. Kuraoka et al (2018) installed a ground-based InSAR (GBInSAR) 4 days before the 2015 eruption to monitor the local uplift observed by satellite InSAR. Fortunately, the 2015 eruption took place within the monitoring area and ground deformation associated with the eruption was recorded with high sampling rate (< 10 min).…”