10.3.5 Earthflows are downslope, viscous flows of saturated, fine-grained materials, which move at any speed from slow to fast (figure 13). Typically, they can move at speeds from 0.17 to 20 km/h. Clay, fine sand and silt, and fine-grained, pyroclastic material are all susceptible to earthflows. The velocity of the earthflow is dependent on water content in the flow itself.  Earthflows occur much more during periods of high precipitation, which saturates the ground and adds water to the slope content. Water then increases the pore-water pressure and reduces the shearing strength of the material.

 

 

         

        Figure 13: example of Earthflows  that damage the city