浅間火山2004年噴火噴出物の岩石学的検討(<特集>2004年浅間山噴火(1))

概要

論文の詳細を見る
The 2004 eruption of Asama volcano, central Japan, was characterized by emergence of small amount of andesite lava in the summit crater, strombolian explosions and a series of vulcanian explosions. There is a good correlation between the degree of differentiation of glass in juvenile ash and repose times between successive explosions. Glass in ash erupted after a long repose time is high in SiO_2 content and crystallinity. In contrast, glass in ash from continuous strombolian explosions is less evolved chemically and is poorer in microlites. The chemical compositions of the evolved glasses in the Qz-Ab-Or diagram suggest that the magma was degassed at lower pressures. This is supported by low H_2O contents of the least vesicular rinds on bread crust bombs. In addition, complexly deformed fragments of white-colored volcanic sediment containing high SiO_2 glass and silica minerals, which probably originated from beneath the volcano, shows substantial heating evidenced by partial melting of the sediment and further modification by strong shearing along the conduit wall during magma ascent. The eruptive sequence can be modeled, as follows; 1) magma emerged continuously in the summit crater, accompanied by strombolian explosions (lava emergence and strombolian stage). 2) Magma became stagnant and crystallized at a shallow level in the conduit (repose period and crystallizing stage). 3) Vulcanian eruption occurred when crystallizing magma was pressurized by addition of new magma and/or gas accumulation sufficient to overcome the strength of a lava plug present below the crater (vulcanian stage). The 2004 eruption was marked by repetitions of this cycle and the conduit probably was choked when magma supply stopped. The deformed nature of volcanic sediment entrapped as xenoliths suggests significant shearing between viscous magma and the conduit wall.
特定非営利活動法人日本火山学会の論文
2005-10-31

浅間火山2004年噴火噴出物の岩石学的検討(<特集>2004年浅間山噴火(1))

スポンサーリンク

概要

著者

関連論文

スポンサーリンク