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Zao
"The Zao volcano group, the most active of northern Honshu, consists of a complex cluster of stratovolcanoes straddling the Pacific Ocean-Japan Sea divide. The Pleistocene Ryuzan volcano forms the western Zao group (Nishi-Zao), and Byobu and Fubo volcanoes form the southern Zao group (Minami-Zao). The complex was constructed over granitic basement rocks as high as 1500 m and thus has a relatively small volume. The 7 cu km Zao volcano proper forms the central ao group (Chuo-Zao), a volcanic complex topped by several lava domes and the Goshiki-dake tuff cone, aligned along a NW-SE trend. Several episodes of edifice collapse produced debris avalanches during the Pleistocene. Goshiki-dake contains the active Okama crater, filled with a colorful, strongly acidic crater lake (pH 1.3). It has been the source of most of the frequent historical eruptions of Zao volcano, which date back to the 8th century AD."  -Smithsonian Volcano Archive
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