報告書番号

U98015

タイトル（和文）

湖沼堆積物を用いた手賀沼の環境変遷の検討（その１） -－手賀沼の特徴とその変遷および音波探査による地質構造－-

タイトル（英文）

Investigation of environmental change on the Tega Lake based on lake sediment analysis(Part 1)-Property of the Tega Lake, its transition and sedimentary structure based on sonic prospecting analysis-

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究では，湖沼堆積物の形成要因と手賀沼での環境変遷について整理した．手賀沼が現在のような閉鎖性の水域になったのは，縄文海進期以降の海水準の低下と河川の人為的な補修工による影響による．手賀沼の周辺環境の変化はごく近年に始まっており，昭和に入るまで，ほとんど開発がなされてなかった． 音響測深と音波探査によって，手賀沼の水深と湖底下の堆積構造を調べた．この結果，湖底に３層が確認された．上の層は，ごく近年に堆積した含水率の高い非常に軟弱な泥からなる層，真ん中の層は，縄文海進期以降に堆積したやや固結した泥質堆積物，下位の層は最終氷期以降，縄文海進期以前に堆積した砂質堆積物に相当する．

概要 （英文）

In this study, factors of forming lake sediment and environmental changes in the Tega Lake are discussed. The Tega Lake became an enclosed water area like present, because of influence of sea-level fall since the Jomon Transgression and also artificial repair of rivers. And circumference of the Tega Lake began to be developed in very recent years, until early in Showa period, there was almost undeveloped. Water depth of the Tega Lake and sedimentary structure under the lake bottom have been investigated by echo-sounding and sonic prospecting. The result of sonic prospecting indicates that 3 layers exist under the lake bottom. The upper layer consists of soft muddy sediment of high water content in very recent years, the middle layer is a little compacted muddy sediment that was deposited after the Jomon Transgression Period and the lower layer is sandy sediment that was deposited between the end of last glacial period and the Jomon Transgression Period.

報告者

キーワード