The term landslide refers to a rapid displacement of a mass of rock, residual soil, or sediments adjoining a slope, in which the center of gravity of the moving mass advances in a downward and outward direction. A similar movement proceeding at an imperceptible rate is called creep. The velocity of the masses involved in a typical landslide increases more or less rapidly from almost zero to at least 1 foot per hour. Then i t again decreases to a small value. By contrast, typical creep is a continuous movement which proceeds at an average rate of less than 1 foot per decade. Higher rates of creep movements are rather uncommon.