International Workshop on the mechanism of Phreatic Eruption

Review of Ground-Based Interferometric Synthetic Aperture Radar formonitoring of ground deformation in areas of volcanoes
Senro Kuraoka1

1 Research and Development Center, Nippon Koei Co., Ltd.
E-mail: a4982(at)n-koei.co.jp

Ground-based interferometric synthetic aperture radar (GB-InSAR) has been developed andapplied over the past two decades for areal monitoring of surficial ground deformation.
Lauren et al (2019) notes the potential application of GB-InSAR in detecting grounddeformation as precursors of hazardous eruption and/or slope instabilities within volcano
hazard areas. However, the monitored surficial deformation is a consequence ofcompounded mechanisms attributed to ground inflation and/or subsidence associated withmagma rise or variations in hydrothermal systems and/or gravity-driven slope movements.
Hence, evaluation of the risk and planning the mitigation measures are challenging issues.
Two cases of monitoring by the GB-InSAR in Japan are reviewed herein to further discuss
the applicability and future research issues of GB-InSAR. The first case is an observation of
long-term gravitational deformation of hardened lava that pose potential risk to the public ofShimabara city in Nagasaki Japan. Monitoring by GB-InSAR helped understand thedeformation mechanisms which are needed for planning the early warning (Fig. 1).

Fig. 1 The structure of lava lobes and the distribution of displacement obtained by GB-InSAR.
Areas of relatively large deformation may be, in part, attributed to the consolidation of thedebris deposits under the lower half region of the lava 11B (Satou et al. 2014).

International Workshop on the mechanism of Phreatic Eruption

The second case presents the monitoring of the deformation of an eruption center during
the 2015 phreatic eruption of Hakone volcano, Japan. GB-InSAR was installed 4 days before
the eruption of Hakone volcano on June 29th, 2015. The ground deformation observed by
the GB-InSAR began suddenly on the morning of June 29th almost coincident with theintrusion of hydrothermal fluid that was inferred by other geophysical observations. The GBInSAR results indicated 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 (Kuraokaet al. 2018). The author also notes the blue and green lines in Fig. 2 which indicate possibilityof slope movements induced by the variation of underground stresses and/or vibrations.

Fig. 2 Time variation of the relative displacements of the five selected areas, magnitude andcumulative number of seismic events (Kuraoka et al. 2018).
Main References
Lauren N S, Federico D T et al. (2019) Monitoring volcano slope instability with Synthetic
Aperture Radar: A review and new data from Pacaya (Guatemala) and Stromboli (Italy)
volcanoes, Earth-Science Reviews Volume 192, May 2019, Pages 236-257.
Satou Y, Ishizuka T et al. (2014) Deformation Characteristics of Unzen Lava Dome based onLong Range Displacement Monitoring, INTERPREAVENT, Nara Japan.
Kuraoka, S., Nakashima, Y., et al. (2018) Monitoring ground deformation of eruption centerby ground-based interferometric synthetic aperture radar (GBInSAR): a case study
during the 2015 phreatic eruption of Hakone volcano. Earth Planets Space 70 (1), 181.