TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 52 (No. 11), pp. 1015-1018, 2000


GPS and EDM monitoring of Unzen volcano ground deformation

Takeshi Matsushima1 and Akimichi Takagi2

1Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, Shimabara 855-0843, Japan
2Seismolgical and Volcanological Department, Japan Meteorological Agency, Tokyo 100-8122, Japan

(Received January 13, 2000; Revised June 14, 2000; Accepted July 14, 2000)

Abstract: Following 198 years of dormancy, an eruption started at Mt. Fugen, the main peak of Unzen volcano, in Kyushu, Japan, in November 1990. A dacite lava dome began to grow in May 1991. We installed the surveying points of GPS in 1992 around the lava dome in order to observe the ground deformation that accompanied the growth of the lava dome. In the winters of 1993 and 1994, we observed swift ground deformations that radiated from the vent of the volcano. It was presumed that rising magma accumulated and expanded the volcano body. After the lava effusion stopped in 1995, we also installed surveying points on the lava dome. EDM mirrors were permanently fixed to the large rocks with bolts. A GPS survey was carried out 2 or 3 times each year to estimate the 3-dimensional displacement. The result of the EDM survey showed that the baselines from the flank of the volcano were shortening 5 mm per day, and the result of the GPS survey showed that the displacement vector of the dome was parallel to the direction of the steepest slope of the old volcano body. This indicates that the inside of the lava dome is still very hot, and that deformation of the dome is viscous.

Corresponding author E-mail: mat@sevo.kyushu-u.ac.jp

[Full text] (PDF 1.7 MB)