When a release of gas, or of gas and mist has occurred it disperses into the atmosphere. Dispersion is initially due to violent mixing, in a turbulent jet, if the release is through a hole, or in a "blow up" of gas (violent mixing). These phenomena often dilute the release by a factor of 10 or more, within a short distance from the origin of the release. After this point, further dispersion depends on whether the mixture of gas and air is heavy or not. If it is heavy it will disperse initially as a layer, close to the ground. If it is lighter than air the dispersion will take the form of a rising plume.