ash flow

Pyroclastic flows, also known as nuées ardentes or glowing avalanches, are a highly dangerous aspect of explosive volcanic eruptions. These flows are fluidized mixtures of hot rock fragments, gases, and air that travel at high speeds, hugging the ground. They can reach speeds of up to 160 km (100 miles) per hour and temperatures between 100 to 700 °C (212 to 1,300 °F), incinerating nearly everything in their path.12

Pyroclastic flows can form when an ash column becomes too dense to rise or when they pour over the lip of a vent. They are distinct from lava flows, which are composed of molten rock and move much more slowly. While ash falls from eruptions generally don't cause direct fatalities, they can lead to roof collapses and crop failures. The 2010 eruption of Iceland's Eyjafjallajökull volcano produced an ash cloud that significantly disrupted air travel across Europe.1234