階地邊坡演育過程的研究，有助於釐清邊坡形態與邊坡地形作用之關係，實乃利 用邊坡形態進行階地定年的基礎。本研究以宜蘭縣蘭陽溪中游夫布爾階地鄰主流沿岸階崖為 研究對象，根據邊坡坡面的組成物質、坡度、沖蝕狀況以及植生情形將階地邊坡劃分成均質 的坡單元，並詳細記錄相關的組成勺形貌和地形作用情況，再將所蒐集到的資料根據此等因 子的特徵進行分類，然後進行統計分析，歸納出各類坡單元與環境因子之間的關係。結果發 現，邊坡組成物質對坡度的影響最具顯著性。野外的觀測發現，階地的自由崖面是以落石或 淺層滑落為改變邊坡形態的主要地形作用，邊坡採間斷後退的方式，其坡度並未與演育時間 有明確的相關。階崖下方的崩積坡則會受到蠕移、雨水濺蝕、土壤沖蝕等作用的影響，而逐 漸減緩坡度，但是一旦上方自由崖面發生崩塌，則會因為堆積物質的增添而再度增高坡度， 因此以目前階崖邊坡尚未被崩積坡完全覆蓋的階段而言，崩積坡的坡度也不會隨著時間穩定 變緩，此時以擴散模式為基礎所發展的邊坡演育模式，顯然不適於用來推估邊坡的演育時間 。

　　　　　Research on terrace slope evolution helps to clarity the relationship between slope form and geomorphological processes, and is essential to geomorphological dating of terraces. The Fu-Bu-Er terrace located in the Lang-Yang stream is the chosen study site. The terrace slopes are delineated into homogeneous units, and the geology, surfacial gradient, erosion and vegetation conditions of each unit are carefully observed and recorded. The collected data are then classified according to material type, morphological characteristics and working processes. Further statistical analyses are performed in order to postulate the relationships between slope form and environmental factors. The author concludes that the geology of terrace slopes is the most significant factor in controlling slope gradient. Field observations reveal that the free scarp slope retreats by periodic rockfalls and debris slumps, thus, no definite relationship exists between slope gradient and the age of the slope. Debris slopes beneath free scarp faces are subject to creeping, rain splash, and soil erosion, and thus start to experience reduction of their gradients. However, when the free scarp face above any debris slope fails, new material accumulates to increase the height and gradient of the debris slope. As long as the free scarp face exists, the gradient of the debris slope will fluctuate but will not diminish with time. As a result, the diffusion-based slope evolution model is not apt for simulating slope change or estimating the age of the slope.