Pyroclastic flow. Illustration of a type of volcanic eruption known as a pyroclastic flow, or nuee ardente (glowing avalanche). This is a highly destructive phenomenon that consists of a very hot cloud of volcanic ash, dust and gases. The cloud cascades down the slopes of the volcano, supported by searingly hot volcanic gases that can exceed 800 degrees Celsius. The low friction of the gas allows the cloud to reach speeds of over 160 kilometres per hour. The cloud will incinerate trees and most objects in its path.