Hazards

Eruptions pose direct and indirect volcano hazards to people and property, both on the ground and in the air. Direct hazards are pyroclastic flows, lava flows, falling ash, and debris flows. Pyroclastic flows are mixtures of hot ash, rock fragments, and gas. They are especially deadly because of their high temperatures of 850� C (1600� F) or higher and fast speeds of 250 km/h (160 mph) or greater. Lava flows, which move much more slowly than pyroclastic flows, are rarely life threatening but can produce massive property damage and economic loss. Heavy accumulations of volcanic ash, especially if they become wet from rainfall, can collapse roofs and damage crops. Debris flows called lahars are composed of wet concretelike mixtures of volcanic debris and water from melted snow or ice or heavy rainfall. Lahars can travel quickly through valleys, destroying everything in their paths.