Earthflows are just one type of
mass movement that can occur on a hill slope. It has been recognized as its own type of movement since the early 20th century. Earthflows are one of the most
fluid types of mass movements. Earthflows occur on heavily saturated slopes like
mudflows or a
debris flow. Though earthflows are a lot like mudflows, overall they are slower and are covered with solid material carried along by flow from within. Earthflows are often made up of fine-grained materials so slopes consisting of
clay and
silt materials are more likely to create an earthflow. As earthflows are usually water-dependent, the risk of one occurring is much higher in humid areas especially after a period of heavy rainfall or
snowmelt. The high level of
precipitation, which saturates the ground and adds water to the slope content, increases the pore-water pressure and reduces the
shearing strength of the material. As the slope becomes wet, the earthflow may start as a
creep downslope due to the clay or silt having less friction. As the material is increasingly more saturated, the slope will fail, which depends on
slope stability. In earthflows, the slope does not fail along a clear shear plane and is instead more fluid as the material begins to move under the force of gravity as friction and slope stability is reduced. == Velocity ==