A nuee ardent, or "glowing cloud," is a type of explosive volcanic eruption characterized by a dense, very hot mass of ash, gasses, and volcanic material traveling down a volcanic slope at high velocity. A nuee ardent, also called a pyroclastic flow, can reach speeds of 450 mi/hr (720 km/hr) and temperatures of 1,500°F (830°C). They can travel as much as 124 mi (200 km) from the source and cover areas as large as 12,000 mi² (20,000 km²). The volume of transported material can be as large as 250 mi³ (1,000 km³) or more.

Nuees ardentes can be destructive and deadly. An eruption of Mount Pelee, Martinique, in 1920 produced a nuee ardent that, within minutes, killed 30,000 inhabitants of a nearby town. In 1982, eruptions and pyroclastic flows from El Chichòn Volcano, southeastern Mexico, killed 2000 people, in villages as far as 5 mi (8 km) from the source.

Nuees ardentes are typically composed of two...