An eruption cloud is a cloud of tephra and gases that forms downwind of an erupting volcano. The vertical pillar of tephra and gases rising directly above a vent is an eruption column.

 

Eruption clouds are often dark colored – brown to gray – but they can also be white, very similar to weather clouds. Eruption clouds may drift for thousands of kilometers downwind and often become increasingly spread out over a larger area with increasing distance from an erupting vent (note fan-shaped eruption cloud in photographs at left). Large eruption clouds can encircle Earth within days.

 

Eruption cloud is often used interchangeably with plume or ash cloud.