Glowing cloud / Nuee Ardente
Nuee Ardente literally means "Glowing cloud" in French and the term was first used to describe the fast moving clouds of hot,ash and dust which devastated the twon of St.Pierre during the eruption of 1902 on Martinique.The term is an alternative for the volcanic hazard pyroclastic flow.
A pyroclastic flow is a fast moving ground hugging surge or avalanche of hot ash,dust aand rocks released from a volcano. The flow appears as a billowing grey cloud moving at great speed down the slopes of a volcano. They consist of hot ash,rocks,dust and gas at a temperature of 100OC and can move at speeds of up to 100km/hour. The grey cloud is the cooled exterior of the cloud and thermam imaging equipment would show them to be very hot. Dome collapse and eruption colomn collapse are the main causes. They can even travel across water. Vesuvius, Soufriere Hills.Mt.Pelee and Mt.St.Helens all produce Pyroclastic flows.