What Is Mass Movement?
Mass movement (also known as mass wasting) is the downslope movement of material on a hillslope that is driven by gravity. This occurs when a geomorphic threshold, the point at which a landform loses its stability, is exceeded and the material on a hillslope is driven out of equilibrium. This is represented in the following equation, showing the relationship between resisting forces on a hillslope (shear strength) and the driving forces (shear stress).  |
| Image Source: Ritter, Dale F., Process Geomorphology. Waveland Press, Inc., 2011 |
F values larger than 1 indicate slope stability, as they show that shear strength is greater than shear stress. Likewise, an F value of 1 indicates when slope failure should theoretically occur, because it shows that shear strength has become equal to shear stress, and thus slope stability can no longer be maintained.