The ascending, vertical part of the mass of erupting debris and volcanic gas that rises directly above a volcanic vent
. Higher in the atmosphere, columns usually spread laterally into plumes or umbrella clouds.
A cloud of tephra
and gases that forms downwind of an erupting volcano is called an eruption cloud
. The vertical pillar of tephra and gases rising directly above a vent
is an eruption column
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 the Earth within days.
Eruption cloud is often used interchangeably with plume
or ash cloud