A pyroclastic flow is a fast-moving current of hot gas and volcanic matter that flows down the slopes of a volcano during an eruption. These flows can reach speeds of up to 700 kilometers per hour (about 435 miles per hour) and can be extremely dangerous due to their high temperatures, which can exceed 1,000 degrees Celsius (1,832 degrees Fahrenheit). Pyroclastic flows are formed when volcanic material, such as ash and rock fragments, becomes too heavy to remain airborne and collapses. They can travel along the ground, following the contours of the landscape, and can destroy everything in their path, making them one of the most hazardous volcanic phenomena.