sentences:  In most cases we think of a trigger as an external stimulus that induces an immediate or near-immediate response in the slope, in this case in the form of the movement of the landslide.Generally this movement is induced either because the stresses in the slope are altered, perhaps by increasing shear stress or decreasing the effective normal stress, or by reducing the resistance to the movement perhaps by decreasing the shear strength of the materials within the landslide.Topography
  
  Geological Factors
  
  Tectonic Activity
  
  Physical Weathering
  
  Hydrogeological Factors
  
  
  In the majority of cases the main trigger of landslides is heavy or prolonged rainfall.