磐梯火山1888年噴火の噴石落下孔  [in Japanese] The impact craters from the eruption of Bandai volcano in AD1888, Northeast Japan  [in Japanese]

磐梯火山は磐梯山・櫛ヶ峰・赤埴山の三峰から成る.1888年7月15日,磐梯火山の頂部で水蒸気爆発が発生し,小磐梯山が崩壊した.岩屑なだれは主に北麓に一部が南東麓に流下した.著者は、1985年,磐梯火山頂部の鏡沼に凹地形を発見した.著者はこれらの凹地形について,現地調査を行い,分布図・断面図を得た.以下の点から,鏡沼に存在する凹地形について1888年噴火で生じた噴石落下孔と結論した.(1)磐梯山1888年噴火の論文に噴石落下および噴石落下孔の記載があること,(2)鏡沼の凹地形の垂直断面が逆円錐形で,開口方向が1888年爆裂火口方向であること,(3)鏡沼の凹地形に噴砂の特徴が見られないこと,(4)1888年噴火のひとつ前の噴火が約1200年前であり,その時の噴石落下孔が現存する可能性が少ないこと,(5)沼底の小石の分布の状態から凹地形が比較的新しい地形であること.また,同様の1888年噴火の噴石落下孔は,沼ノ平や赤埴山にも存在する.

Bandai volcano consists of three peaks of the Bandaisan, Kushigamine and Akahaniyama. On July 15^<th> 1888, a phreatic eruption occurred on the north side of the Bandai volcano. After this eruption, Kobandaisan collapsed. The debris flow went down mostly in the north-eastward direction, however some traveled down on the south-eastward side. In 1985, Chiba discovered concave geographical features in the Kagami-numa, the top of the Bandai volcano. Chiba did field investigations, and created a map detailing position, and created a cross section. From the following points, I reached the conclusion that the concave geographical features of Kagami-numa were impact craters which formed by an eruption of 1888. (1) Some theses at 1888 eruption of Bandai volcano discuss the cinder falls and the resultant impact craters. (2) A perpendicular section of these concave geographical features of the Kagami-numa has the shape of a reverse cone and opens in the direction of the explosion in 1888. (3) The features of the sand boil isn't seen in these concave geographical features in the Kagami-numa. (4) The previous eruption occurred 1200 years before the one in 1888. It is very unlikely that the impact craters of an eruption that occurred 1200 years before still exist. (5) Stones are distributed over the marsh bottom, but stones are not found in these concave geographical features, suggesting that these concave geographical features are new. The impact craters from the eruption of 1888 also exists on Numanotaira and Akahani-yama.