The study in this research consists of a review of two case studies of landslides in natural terrain, parametric study, and a comparison of the computed and observed runout distances of a cluster of landslides. The study leads to the following conclusions. (1) The runout distance increases with the decrease of the angle of friction mobilized or with the increase in the natural terrain inclination. (2) When the natural terrain inclination is approaching the mobilized friction angle, the runout distance is independent of the initial landslide height and is dependent on the natural terrain inclination and debris characteristics. (3) The results of the parametric study have been compared to the observed runout distance of 28 debris flows and reasonable agreement has been obtained.