Pyroclastic flows can originate in a number of ways, including the collapse of a vertical
eruption column of ash, lateral or inclined blasts from the volcano, and the collapse of part of the volcanic edifice. They may move at very high velocities, up to 300m s1, and can have temperatures of over 10008C: a pyroclastic flow made up of a hot mixture of gas and tephra is sometimes referred to as a nue ´e ardente, a ‘glowing cloud’ (Cas & Wright 1987).