南アルプス仙丈ケ岳・藪沢の最終氷期の氷河作用と堆積段丘 Glaciation and Accumulation Terracing in the Yabusawa Valley, Mt.Senjogatake in the Southern Japanese Alps, since the Last Glacial Stage
南アルプス・仙丈ヶ岳緬の薮沢では,氷河地形と鞭物薩づけば最終糊の三っの異なる氷河前進期ないしは停滞期が認められた.氷河は最も古い薮沢1期に,最前進し,その末端高度はおよそ標高2,250m. であった.薮沢II期の氷河は標高2,550m付近まで再前進した.薮沢皿期の氷河の末端高度は標高2,890mで,カール内に留まった.i薮沢1期は最終氷期の初期～中期を,薮沢II期,i薮沢皿期は後期を不すと考えられる.<br> 泥質の厚い薮沢礫層の堆積は,完新世初頭頃,急激に生じた.その形成は氷河作用とは無関係で,山岳永久凍土の融解に関連した山地崩壊による可能性がある.
The chronological formation of glacial landforms and accumulation terracing were examined in the Yabusawa Valley on the north slope of Mt. Senjogatake, Southern Japanese Alps. Glacial land-forms such as glacial troughs, truncated spurs, lateral and terminal moraines, and roches mouton-nees represent three distinct glacial advances and/or standstill called Yabusawa I, Yabusawa II, and Yabusawa III. Yabusawa I is the oldest and Yabusawa III is the youngest. During the Yabu-sawa I substage we determined that the glacier advanced down to an altitude of 2, 250m above sea level based on the glacial trough and its associated trimline. During the Yabusawa II substage the glacier advanced down to an altitude of 2, 550m above sea level as indicated by lateral and terminal moraines (Mu moraine). The bottom of the Yabusawa I glacial trough was shaped by meltwater into a narrow V-shaped valley during the retreat of the Yabusawa I glacier and the advance of the Yabusawa II glacier. During the Yabusawa III substage the glacier remained within the cirque to form a typical terminal moraine (Ms moraine) at 2, 900 m above sea level. Con-sidering the geomorphological development of glacial landforms and the glaciation of the Central Japanese Alps, situated ca. 50 km west of Mt. Senjogatake, the Yabusawa I substage probably repre-sents the early stadial of the Last Glaciation. Both the Yabusawa II and III substages seem to indicate the late stadial of the Last Glaciation. The accumulation of thick gravels within a very muddy matrix, the Yabusawa terrace gravel, occurred rapidly about 9, 000 years BP and was pro-bably associated with slope failure in the surrounding mountains, not with glaciation. This failure was possibly influenced by the melting of mountain permafrost that probably remained in this area during the early Holocene.
- 地理学評論. Ser. A
地理学評論. Ser. A 73(2), 124-136, 2000-02-01
The Association of Japanese Geographers