Bull. Volcanol. Soc. Japan
Vol. 58 (2013) No. 1, pp. 137-151

ArticleVertical Ground Deformation Associated with the Volcanic Activity ofSakurajima Volcano, Japan during 1996-2010 as Revealed by
Repeated Precise Leveling Surveys
Keigo YAMAMOTO＊, Tadaomi SONODA＊, Tetsuro TAKAYAMA＊, Nobuo ICHIKAWA＊, Takahiro OHKURA＊＊,Shin YOSHIKAWA＊＊, Hiroyuki INOUE＊＊, Takeshi MATSUSHIMA＊＊＊,
Kazunari UCHIDA＊＊＊ and Manami NAKAMOTO＊＊＊(Received October 5, 2011 ; Accepted March 2, 2012)
The recent vertical ground deformation in Sakurajima volcano and around Aira caldera associated with thevolcanic activity of this volcano is revealed by the repeated precise leveling surveys conducted in October-December
2007, November 2009 and April and November 2010. The ground uplifts are detected in Sakurajima volcano andaround Aira caldera to be centered in the caldera during the period from 1996 to 2010, as the previous results during theperiod from 1991 to 1996. From the analysis based on a spherical source (Mogiʼs) model, the inflation source is located
6 3
at 8.8 km - 10.8 km depth with the volume change rates of 6.5-8.2×10 m /year beneath the center of Aira caldera
generally through the period of 1996-2010. It is indicated that the magma storage at the inflation source inferred at 10km depth beneath Aira caldera is progressed during the period. In the period of 2007-2009, a shallow inflation source
63is located at 4.3 km depth with a volume change rate of about 0.6×10 m /year beneath the northern part of Sakurajima.
It suggests the magma movement towards shallow part of Sakurajima volcano from 10 km depth beneath Aira caldera,
6 3although the estimated amount of magma input is as small as about 2.0×10 m .The magma storage at the magma
reservoir beneath Aira caldera has continued since around 1991 when the eruptive activity of Sakurajima volcano wasgradually decayed. Explosive eruptions are increasing at Showa crater in Sakurajima volcano especially since 2009.
However continuing ground uplifts are observed until November 2010. It is suggested that the amount of suppliedmagma overcomes that of ejected magma at the magma supply system beneath Aira caldera in spite of the increasing
volcanic activity. Considering the estimated volume increase at the inflation sources and the volume of the ejected
8 3magma based on the observed amount of the ash-fall deposits, it is indicated that the total of about 1.2×10 m magma
is inferred to have additionally stored beneath Aira caldera during the period from 1991 to 2010. The ground upliftaround the northern part of Sakurajima caused by the progressing magma storage at the time of November 2010
recovers and further exceeds the height level in around 1973, when the intense summit eruptions during the 1970s andthe 1980s started. These results suggest the immanent potential of the next intensive eruptive activity of this volcano.
Key words : Sakurajima volcano, Aira caldera, precise leveling survey, vertical ground deformation

1．Introduction
Sakurajima volcano is an andesitic stratovolcano locatedin southern Kyushu, Japan (Fig. 1). It is situated on thesouthern rim of Aira caldera. At this volcano, the flank
eruptions with the lava flows and the summit eruptions
have been repeated during historic times, including thegreat eruption in 1914. The current eruptive activity at thesummit crater of Minamidake began in 1955, which ischaracterized by violent explosive eruptions of a Vulcanian＊

Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, SakurajimaYokoyama, Kagoshima 891-1419, Japan.
＊＊
Aso Volcanological Laboratory, Graduate School ofScience, Kyoto University, Kawayo, Minami-Aso, Aso,
Kumamoto 869-1404, Japan.

type, as well as the intermittent emissions of volcanic ash.
In addition, the eruptive activity at Showa crater on theeastern slope of the volcano started in June 2006 and theactivity has increased in recent years. The total number ofexplosive eruptions since 1955 exceeds 9500 in 2010.
Repeated precise leveling surveys have been conductedin and around Sakurajima volcano since 1957 (Eto, 1967;
Eto et al., 1997; Yoshikawa, 1961). The results suggested
that the ground deformation associated with the eruptive＊＊＊

Institute of Seismology and Volcanology, Faculty ofSciences, Kyushu University, 2-5643-29, Shinyama,Shimabara, Nagasaki 855-0843, Japan.
Corresponding author: Keigo Yamamoto
e-mail: yamamoto@svo.dpri.kyoto-u.ac.jp