Landslides comprising soil, rock, water and organic material are termed debris slides or debris flows, with the distinction between the two made largely to recognize the form of movement along the event path as it progresses downslope. Where initial movement occurs as a slide, it often progresses quickly to a flow as a consequence of strength loss that occurs with movement. Debris flows represent a natural hazard in mountainous terrain around the world. Numerous catastrophic events have occurred in recent years. In contrast to other types of landslide activity, debris flows may be considered to be a ‘low-magnitude highfrequency' hazard. They result in damage to property and, in some circumstances, may also result in loss of life.