地形開闊度分析之地形計測方法能突顯地形角度變化強烈處，是分析地形資訊的利器。本研究利用 1米空載光達測製數值高程模型，藉由地形開闊度計算得到正與負值兩種結果，其正值能反映山脊線、崩崖、階地，負值則為河谷、水系與蝕溝分布等構造地形，並進一步由紅色立體投影圖同時展現正負兩地形開闊度之凸凹特性，以判釋出草嶺地區之微地形特徵。最後，由負地形開闊度(灰階)搭配坡度分析 (紅階)細部判釋草嶺山崩之崩塌面蝕溝於不同岩層分布，並估算出 1999-2011年期間卓蘭層及錦水頁岩基岩下切侵蝕速率分別為平均每年下切 31-39公分、54- 89公分，顯示錦水頁岩抗蝕力較弱。

Openness methods can visualize the topographic character of angular measure between surface relief and horizontal distance; it is a useful tool for determining geomorphic fractures. We adopted the high-resolution Airborne LiDAR (Light Detection And Ranging) DEM to obtain the positive and negative values. Positive shows reflect ridge, scarp and terrace, whereas negative describe valley, river and gully. Red Relief Image Map (RRIM) can identify fine-scale geomorphic change when it is combines the positive and negative values. Many of the characteristics that obtained from the negative calculation (marked in gray-scale) and an analysis of stacked slope (marked in red-scale), to interpret the position of eroded gullies in the Tsaoling sliding area. In this study, we investigated the distribution of erosion gullies and calculated the bedrock incision rate for the Cholan Formation and Chishui Shale for 1999 and 2011, which were 31 to 39 cm/year and 54 to 89 cm/year on average, respectively. These results indicated that the Cholan Formation has a higher resistance to erosion than the Chishui Shale, where the erosion was more serious.