BackgroundThe andesitic-dacitic volcano rises about 800m above the sea floor and consists of 2 somma volcanoes, the (probably older) Biro-yama forming the southern half of the island, and Naka-dake in the center and northern half.
Mi-take (Ontake) is a lava dome that had grown inside Naka-dake's caldera and forms the summit of the island.
Omune is the local name of gently sloping plateau on the top of the cliff at the northeastern end of the island. In this area, a ca. 100 m thick dacitic lava flow was sampled and dated recently a recently. The K-Ar ages was <80,000 yrs Before Present, but its youthful morphology and the absence of any tephra layers above suggest it could be as young as the Holocene (i.e. less than 10,000 years old).
The Omune lava flow, after the Kikai rhyolite the most SiO2-rich lava known in the Tokara islands, is the youngest product of Akuseki-jima volcano, forms a low-angle plateau overlying cliffs forming the northern coast.
Source: Furuyama K, Daishi M, Nagao K, Eguchi M (2002). "The discovery of young dacite lava in Akuseki-jima Island, Tokara Islands, Japan" Bull Volc Soc Japan (Kazan), v.47, pp 751-755
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