A flowing, often somewhat conical, trail of emissions from a continuous point source, for example the plume of smoke from a chimney. As a plume spreads, its constituents are diluted into the surrounding medium. When plumes disperse in media with high turbulence, they can take on more complex shapes with loops and meanders. This somewhat chaotic nature has lead to probabilistic descriptions of the concentration of materials in plumes; for example, calculations concerning the downstream impact of pollutants released from pipes and chimneys will be couched in terms of average concentrations. Typically plumes are found in air or water, but plumes of trace contaminants may also be found in less-mobile media such as soils.