Ash flow refers to the movement of volcanic ash and other pyroclastic materials during an explosive volcanic eruption. This mixture of ash, pumice, and gas can travel rapidly down the slopes of a volcano, often reaching speeds of up to 700 kilometers per hour (about 435 miles per hour). These flows can cover large areas, burying landscapes and affecting ecosystems. The density and temperature of ash flows can cause them to behave like a fluid, allowing them to flow over and around obstacles. Understanding ash flows is crucial for assessing volcanic hazards and protecting communities near volcanoes.