|Region:||Japan, Taiwan, Marianas|
|Measurement method(s):||InSAR, GPS - continuous, GPS - campaign, Levelling, Strainmeter, Tiltmeter|
|Duration of observation:||1892 - present (levelling), 1996 - present (GPS), 2006 - 2012 (InSAR), 1987 - present (tilt), 1990 - present (strain)|
|Inferred cause of deformation:||Magmatic|
|Characteristics of deformation:|
Aira caldera is located within Kagoshima Bay at the southern end of Kyushu in Japan. Sakurajima, an active andesitic stratovolcano, sits on the southern rim of the caldera. It is Japan’s most active volcano, often experiencing daily Vulcanian eruptions.
Aira caldera, and Sakurajima in particular, are closely monitored by the Sakurajima Volcano Research Centre – part of the University of Kyoto and Disaster Prevention Research Institute. Deformation has been recorded at Aira caldera since 1892 with campaign levelling surveys. This captured the 1m of subsidence associated with the 1914 Plinian eruption of Sakurajima. More recently, the volcano is continuously monitored with GPS, tiltmeters and strainmeters. These are supplemented with campaign GPS and levelling surveys, and sporadic InSAR acquisitions.
The recent deformation patterns show a large-scale radial outwards bulge with continual inflation, centred within the caldera. Between 1996 and 2007, GPS results indicated a maximum inflation rate of ~1.5 cm/yr (Iguchi, 2013; Hickey et al., 2015). This has generally been interpreted as magma supply to a deep reservoir beneath the caldera, with an average magma supply rate of ~107 m3/yr (Iguchi, 2013; Hickey et al., 2015). The location of the deformation source is somewhat undefined. ‘Mogi’ model results place it directly beneath the centre of the caldera at 8 – 11 km depth (Iguchi, 2013; Pepe et al., 2013), or alternatively slightly south of this beneath the northern edge of Sakurajima (Yokoyama, 2013). Finite Element model inversions accounting for topography and three-dimensional crustal mechanics as well as thermal effects indicate a large oblate shaped reservoir beneath the north-eastern quadrant of the caldera at a depth of 13 km (Hickey et al., 2015).
Alterations to the general large scale inflation pattern are thought to be caused by a second, shallower (3 – 6 km) deformation source inferred as a short-term magma reservoir (Iguchi, 2013; Pepe et al., 2013), and/or magma flowing between the two sources (Hidayati et al., 2007; Iguchi, 2013; Hickey et al., 2015).
|Reference:||Iguchi, M. (2013), Magma movement from the deep to shallow Sakurajima volcano as revealed by geophysical observations, Bulletin of the Volcanological Society of Japan, 58(1), 1–18.|
|Reference:||Hickey, J., J. Gottsmann, M. Iguchi, and H. Nakamichi (2015), Persistent inflation at Aira caldera accompanying explosive activity at Skurajima volcano: Constraining deformation source parameters from Finite Element inversions, in EGU General Assembly, Vienna, Austria.|
|Reference:||Pepe, S., D. Trippanera, F. Casu, P. Tizzani, A. Nobile, Y. Aoki, S. Zoffoli, V. Acocella, and E. Sansosti (2013), The 2006-2012 deformation at Sakurajima stratovolcano (Japan) detected via spaceborne multisensor SAR Interferometry, in EGU General Assembly, Vienna, Austria.|
|Reference:||Yokoyama, I. (2013), An interpretation on secular changes in deformation caused by the 1914 eruption of Sakurajima volcano, Bulletin of the Volcanological Society of Japan, 58(1), 77–90.|
|Reference:||Hidayati, S., K. Ishihara, and M. Iguchi (2007), Volcano-tectonic earthquakes during the stage of magma accumulation at the Aira caldera, southern Kyushu, Japan, Bulletin of the Volcanological Society of Japan, 52(6), 289–309.|
A view of Sakurajima from the east during a Vulcanian eruption in July 2013. (Photo credit: James Hickey)
Timeseries of levelling data showing the vertical displacement of a benchmark close to the inferred centre of deformation. The 1 m of subsidence associated with the 1914 eruption is abundantly clear. Insets show the most eruptive activity and weight of erupted ash. (Image credit: James Hickey, PhD Thesis, University of Bristol, 2015)