Landslides pose significant risk to the communities and infrastructure, particularly in mountainous regions. Accurate estimation of landslide slip surface depth/geometry and volume of displaced material is crucial for hazard assessment, borehole planning and mitigation strategy. This study presents a novel, cost-effective method based on spline interpolation to estimate the depth of slip surface using Digital Elevation Model (DEM) data, especially in areas with limited field data. The method relies on exposed boundary scarps, making it particularly useful for failed slopes with debris cover or well-developed slow-moving landslides where the slip surface is underneath the sliding material. The approach is validated through two case studies in Western Canada, the Hope Slide and the Downie Slide. The results demonstrate that the interpolated slip surface geometry, provided depth estimates and volume distributions that align closely with existing data, with a maximum volume of about 61 million m3 for the Hope Slide and 0.9 billion m3 for the Downie Slide. As the method is iterative, the stopping criteria can be decided on meeting a certain slope angle, depth or volume depending on the requirements. Further, the algorithm is flexible to include any additional data related to the slip surface in form of 3D exposure planes or 1D borehole depths. This was tested on the case studies by providing additional data and showing improved results on estimating the final slip surface geometry. Beyond landslides analysis the method can be applied for topographic corrections and removing deposited material from other surface processes.
