倒鉤狀流路必然是襲奪灣嗎？－花蓮鯉魚潭地區的地形演育

Do All Elbows Mean Capture?-The Landscape Evolution of Leeyutan Area

齊士崢(Shyh-Jeng Chyi)

《環境與世界》 1期 (1997/11) Pp. 123-135

https://doi.org/10.6304/EAW.1997.1.7

摘要

因為花蓮鯉魚潭地區具倒鉤狀流路、通谷、風口、失能河和堰塞湖等地形特徵，所以被認為曾以發生河川襲奪。由區域地形特徵的調查、分析，本地區的確曾經發生河川轉向，不過這應是由木瓜溪和支流文蘭溪，及曾屬木瓜溪支流的荖溪、白鮑溪發育沖積扇，加積幷堰塞通谷，形成沖積堰塞湖，滿溢的湖水或洪水越過低矮分水嶺再下切造成的河川轉向，而不是河川襲奪。至於沖積扇的形成，推測是全新世中、晚期，全球海水面大規模上升，造成木瓜溪下游加積後，又因氣候變動與持續的地盤上昇運動，使各流域回春幷集中發生大量崩山所致。

關鍵字

地形演育 ； 河川轉向 ； 河川襲奪 ； 河階地 ； 沖積扇

並列摘要

The stream capture model has been proposed to explain the landscape evolution of Leeyutan area for more than forty years; due to those barbed drainages, underfit rivers, through valley, wind gap and dammed lake. Instead of this model, this study suggests divide breaching, a type of stream diversion, is more appropriate. The major mechanism of river overtopping lower divide is the development of alluvial fans. The principal river valley had been first aggradated during the period of late Pleistocene's eustatic sea level rising. Then alluvial fans were formed because of rejuvenating of rivers and climate fluctuation during mid to late Holocene, when eustatic sea level has been relative stable.

並列關鍵字

landscape evolution ； river diversion ； river capture ； river terrace alluvial fan