小値賀島単成火山群における噴石丘の形成発達過程

概要

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Ojika-Jima monogenetic volcano group (OMVG), northwestern Kyushu islands, contains over 41 monogenetic volcanoes of Quaternary age. These volcanoes could be divided into three types in terms of evolution: 1) Single volcanoes subdivided into scoria cone and hybrid cone (maar or tuff-ring+scoria cone+lava flow), 2) Multiple cone which consists of several contemporary cones on branched off vent system, 3) Composite cone, complex of several cinder cones of the different age. These traces of eruption record a four-stage eruptive cycle that was largely or wholly repeated at many cinder cones in OMVG. Stage I were the first phenomenon at many cones whose initial erupted products were exposed as deposits of base surge and pyroclastic fall. Stage I only occurred during the opening stages of eruption at any vent. Stage II began with a lava fountain which produced densely welded layers due to sufficiently high magma ascent rate after bubble growth was sufficiently high. After magma incubation period, the eruption style changed to Strombolian explosions (stage III). Fall back of tephra into the crater and inner-wall collapse, partially blocking the vent, caused vent-cleaning eruption. Finally lava flow emitted from cinder cone (stage IV).
特定非営利活動法人日本火山学会の論文
2001-11-20