Assessment of geomorphic threshold is a significant parameter in landslide studies. The present study dealt with critical slope angle (c φ ), critical rainfall (c r ) and critical height (c h ) of the Paglajhora Sinking Zone. This sinking zone is located in the representative mountain watershed, the Shiv-khola of Darjiling Himalaya, West Bengal. To estimate critical slope angle (c φ ), a Mohr stress Diagram was developed using triaxial compression test parameters such as cohesion (c), major

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... cipal stress (σ 1 ) and minor principal stress (σ 3 ). Thickness of total soil (h), thickness of saturated soil (z), wet soil density (Ps), density of water (Pw) angle of repose () and slope on scar face () were assessed study the stability condition of the hill slope. The directional slope length and effective contour length were taken into account to determine upslope contributing area and critical rainfall (c r ) of major landslide locations. The critical height (c h ) was derived for the initiation of landslips incorporating cohesion (c), angle of internal friction (), unit weight of materials (γ) and slope angle (). Keywords: Paglajhora Sinking Zone, Critical slope, critical height and critical rainfall and geomorphic thresholds. I=73.90D -0.79 ........................... (1). Where, I is the hourly rainfall intensity in millimeters (mm hr-1) and D is duration in hours. Dahal et al. 2006a , while other works, such as Caine and Mool (1983 ), and Dhakal et al. (1999 focused mainly on landslide risk assessment in Himalayan terrains by analyzing physical properties of landslides and debris flows, effects of regional and local geological settings, and recommendations for environmental-friendly preventive measures.