式根島流絞岩質溶岩流にみられる二次火口と放出物

概要

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There are many small inlets ranging from 100 to 200 m in diameter at the marginal of Shikinejima rhyolitic lava flow, Izu-Mariana Arc. Many volcanoclastic dykes (spiracles) are widespread on the inlet-wall, and on the lava surface, some thin pyroclastic-current deposits composed of coarce ash and lava-fragments which range widely in size and vesicularity. The deposits contain water-quenched breccia. Total thickness of the deposits is thickest in the eastern part of the island and thins toward the eruptive center (western part) of this lava flow. The deposits are divided into the following two units: massive unit which resembles the pyroclastic-flow deposits, and laminated unit which resembles base-surge deposits. The flow texture of the sedimemts and the impact structure around the inlets indicate that the explosive events occurred at the inlets. All of these geological features can be explained by explosions due to the destmction of water-steam equilibrium in the steam reservoir fomed beneath the hot lava flow.
特定非営利活動法人日本火山学会の論文
1996-11-15