The plan lane from where moving mass separates to rest mass is failure plane. The shape and position of failure plane surface governed by

(i) pore water pressure and

(ii) variations of shearing strength within the earth masses.

Generally, the surface of failure is circular. The shearing stress and shearing strength are assumed to to be uniformly distributed along the slip surface, Force on the sliding surface are driving force & resisting force. Driving force is the force resulted from the weight of the underlying material, such as rock, soil-vegetation and man-made structures that cause failure while resisting force is caused by the shearing strength of the material acting on the slip surface.

When driving force is greater than the resisting force, slide occurs. In rocks and soils as in other material, a failure flows the pattern of the least resistance. In more or less homogeneous cohesive soil like clays, a slope wood fails primarily by shear and the shear surface would be approximately circular. Thus, rotational slides are produced. The rotational slides take place first by little jerks and the later gradually destroying the bond along the slip surface and the separating mass slumps down. Hence, the term "slump" is used for this kind of slide. If the shearing strength of the earth material is less in horizontal direction than in the vertical direction, the circular arc may be flattening out. Conversely, cases of steeping of the circular arc may also be observed.

If the soil or rock deposit is stratified, the upper strata may Slide down with respect to the lower strata along the boundary, which in this case becomes the slip surface. Such movement of mass through the slip surface is called translational slide. Common cases of translational slides are slab slides in which the slip surface is roughly parallel to the ground surface.

Rotational slides occur on steeper slopes and are of relatively limited length but transnational slides occur on gentle slopes and are usually long. The removal of the lateral support (particularly the removal of the top of the slope for emplacement of building or a highway) is one of the very common causes of the slide. If the material homogeneous, rotational slide may occur where slide may occur if the material has tendency to slide along a plane. Rational slides usually develop from tension scars in the upper part of a slope. The tension cracks at the head of a rotational slide are generally concentric and parallel to the main scar.