Aogashima volcanoAogashima is a beautiful lonely island, 300km south of Tokyo, and is surrounded by sea cliff. The last eruption is AD1783-1785.
Quaternary volcanoes DB in Japan (Aogashima)
Geological map (Takada, 1992, 1994)
Geology of Aogashima Volcano
The edifice volume: about 30 km3 // The relative height from the sea bottom: 1100 m // The highest peak: Otonbu, 423m // The population: a villege of 200 people on the northernwest slope.
The history of Aogashima Volcano (about 3 km3 in volume) (Takada et al., 1992; 1994).
(1) [Pre Main stratocone] The growth of Kurosaki Volcano (0.3 km3) in the northwestern area of Aogashima island.
(2) [before 3000 y.B.P.] The construction of the main edifice of Main stratocone in the southeastern area.
(3) [~3,500 y.B.P.] Fissure eruptions of Aphyric basalts (<0.1 km3) on the northwestern flank.
(4) [~3,000 y.B.P.] A surge activity (Ojiroike Surge Deposits) .
(5) [3,000-2,400 y.B.P.] The eruptions of Kintagaura Lavas (0.15 km3) filling the southeasern basin, and airfalls (Yasundogo Aairfalls Tephras) (0.4 km3) on the east and north flanks.
(6) the occurrence of a debris avalanche (Nagashizaka Debris Avalanche Deposits) associated with the formation of the Ikenosawa Crater (1.7 km x 1.5 km in size).
(7) [A.D. 1781-1785] the Tenmei eruption (0.08 km3) (an ash fall in 1781; an scoria fall in 1783; intermittent ash falls in 1785; lava flows in the Ikenosawa Crater) (SiO2=61%).
// Aogashima Volcano is composed mainly of tholeiitic basalt (SiO2= 49-63%). During the development of Aogashima volcano, magma paths were shifted over a distance of about 4 km. The chemical composition of magma changed with the shift in magma path. The magma-supply rate of Aogashima volcano was fluctuating in time and space with the growth of each geological unit, which may have led to the generation of andesite magma.