Figure 16.25(a) A debris avalanche is the fastest type of unconsolidated flow because of its high water content and movement down steep slopes. (b, c) In 1970, an earthquake-induced debris avalanche on Mount Huascarán, Peru, buried the towns of Yungay and Ranrahirca, killing some 18,000 people. The avalanche traveled 17 km at a speed of up to 280 km/hour and is estimated to have consisted of up to 50 million cubic meters of water, mud, and rocks.