Akan Caldera

...Although it is a lake at the bottom of a caldera, the shoreline is very curved. The Akan Caldera was formed by collapse after violent volcanic activity in the middle of the Pleistocene, and the outer rim can be traced as an ellipse with a long axis of 20 km and a short axis of 13 km, excluding the southern part. The lake, which was initially formed at the bottom of the caldera, was filled in by the eruptions of the three volcanoes Furebetsu, Fuppushi, and Meakan as the lake surface dropped due to erosion by the Akan River. Then, in the early Alluvial Epoch, the central crater cone Mount Oakan became active and created a new dammed lake. However, subsequent activity caused Mount Oakan to grow and fill in most of the lake surface, forming the present Lake Akan, as well as Panketo on the northern foot and Penketo on the eastern foot.

*Some of the terms mentioned in "Akan Caldera" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…カルデラ底にある湖だが，湖岸線は屈曲が多い。阿寒カルデラは，洪積世中期の激烈な火山活動ののち陥没によって形成されたもので，南部を除けば，長径20km，短径13kmの長円形に外輪山をたどることができる。はじめカルデラ底に形成された湖は，阿寒川の浸食により湖面は低下し，フレベツ，フップシ，雌阿寒の3火山の噴火により埋め立てられ，次いで沖積世初期に中央火口丘雄阿寒岳が活動に入って新たに堰止湖を作ったが，その後の活動によって雄阿寒岳は成長するとともに湖面の大部分を埋めて，現在の阿寒湖のほか北麓にパンケトウ，東麓にペンケトウなどを作った。…

※「阿寒カルデラ」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報