The Kuju Volcanic Group consists of over twenty lava domes and small stratovolcanoes. It has effused 22.3 km3 of magma, consisting of lavas (15.5 km3), pyroclastic flows/surges and debris avalanches (4.4 km3 and fallout tephra (2.5 km3). The average magma discharge rate is 0.15 km3/ky. Most lavas formed hornblende andesitic and dacitic lava domes except for the Hiijidake which is a basaltic stratovolcano. Based on eruption types and rate, the eruptive history of the Kuju Volcanic Group can be divided into four stages: K1, K2, K3 and K4. The K1 stage (150 to 110 ka) is characterized by hornblende dacitic ignimbrite eruptions that formed the Miyagi and Shimosakata ignimbrite. The activity of K2 stage (110 ka to 60 ka) occurred in the western part of the group. More than eight lava domes of two-pyroxene hornblende andesite were formed, some with associated explosive activities that generated sub-plinian eruptions forming Hotokenoharu pumice-fall and Miyakono scoria-fall deposits. The K3 (ca. 54 kBP) is the most catastrophic and voluminous eruptive stage. The stage began with Kuju D ash-falls. Large-scale plinian eruptions formed the Kj-P1 pumice-fall deposit with a volume of 6.2 km3. During the plinian eruptions, the northern and southern portions of the eruption column collapsed, and generated the Handa ignimbrite. The Handa ignimbrite attained a volume of 5 km3. Some parts of the Kj-P1 pumice-fallout deposit were deposited atop the Handa ignimbrite, which makes this eruption a typical intraplinian type with a DRE volume of approximately 4.1 km3. A small-scale caldera might be formed during the K1 and K3 stages. The K4, a post-caldera stage can be divided into three sub-stages. During 49 cal kBP to 35 cal kBP, Hosshozan and Ogigahana hornblende-andesite domes emerged, and Kan’nojigoku and Shirani block-and-ash flow deposits had originated from them. Sub-plinian eruptions at Shirakuchidake volcano formed Itakiri lapilli fallout. The period during 32 to 7.3 cal kBP emplaced various magmas of basaltic to dacitic composition. A basaltic activity in this sub-stage formed Hiijidake stratovolcano (lava flows, Nagayu and Hiijidake scoria-fallouts and debris avalanches). During this period, many lava domes were also formed such as Hizengajo, Kujusan, Dainoyama, Mimatayama and Inaboshiyama volcanoes. Sector collapse of Kujusan and Dainoyama lava domes produced the Azamidai and Dainoyama block-andash flow deposits, respectively. Mimatayama eruption started with phreatomagmatic eruption forming Sugamorigoe pyroclastic surges. This is followed by the growth of the Older Mimatayama lava dome with the associated Sugamorigoe block-and-ash flows. The lava domes collapsed generating the Matsunodai debris avalanches. After the collapse, Younger Mimatayama lava domes grew inside the horseshoe shaped crater. After 7.3 cal kBP, the eruption centers moved to the east and the magma rate increased from 0.07 km3/ky to 0.51 km3/ky. The large andesite to dacitic lava domes of Yuzawayama, Tacchusan, Taisenzan, Kurodake were formed. Taisenzan is a complex andesitic stratovolcano. Later vulcanian eruptions formed Danbaru crater and Kj-A1 ash falls. The sub-plinian eruption deposited the Danbaru scoria-fallout. The vulcanian and sub-plinian eruptions generated the Komekubo ash and scoria fallout. The largest eruption at 1.6 cal kBP formed the Kurodake lava dome with a volume of 1.6 km3.
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