Debris-avalanche definition is - a mass of rock fragments and soil that has moved rapidly down a steep mountain slope or hillside and because of its high water content has behaved like an avalanche of snow. A landslide scarp on the island of Hawaii left by a debris avalanche that occurred less than https://www.thoughtco.com/mass-wasting-and-landslides-1434984 The movement of debris or rocks down a slope in a similar manner is also known as avalanches. Flows are further subcategorized depending upon the geological material, for example, earth, debris, and bedrock. (See avalanche.) There are two general types of debris avalanches, cold and hot. Numerous human activities like skiing can also trigger an avalanche. Avalanches tend to grow in volume and mass as they accelerate down the slope. A typical landslide travels at 10 miler per hour, but can exceed 35 miles per hour. Such causes can arise from a number of happenings. Triggered by earthquake shock or torrential rain in mountainous relief with steep gradients, a huge volume of avalanching rock or debris (of up to millions of metric tons) can reach a velocity of more than 50 metres (160 feet) per second and leave a long trail of destruction. This type of landslide is categorized into five; earth flows, debris avalanche, debris flow, mudflows, and creep, which include seasonal, continuous and progressive. Worldwide, landslides occur and cause thousands of casualties and billions in monetary losses annually. [Debris avalanches are not confined to strato-volcanoes, they also occur on shield volcanoes] Map showing debris avalanches (brown) associated with all of the Hawaiian volcanic islands (green). Large-scale avalanches normally occur on very steep volcanoes. On steep hillsides, debris flows begin as shallow landslides that liquefy and accelerate. As avalanches were not unusual in the area, it was common knowledge that there was usually a 20 to 30 minute gap between the sound of the ice cracking off and an avalanche… Casualties in the United States are primarily caused by rockfalls, rock slides, and debris flows. Landslides in the United States cause approximately $3.5 billion (year 2001 dollars) in damage, and kill between 25 and 50 people annually. What Causes Debris Avalanches and Debris Flows? For example; (a) Increase in the mass of weak rocks, clay and other debris likely to slide; The most common cause of debris avalanches and debris flows is the combination of heavy rainfall, steep slopes, and loose soil. The danger of relying on triggers to ascertain the probability of failure is exemplified by the Guinsaugon event; in the lag time between the end of the period of heavy rainfall and the occurrence of the rockslide-debris avalanche, evacuated residents had returned to their homes. 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