Atmosphere And Weather
Pyrocumulus cloud

Overview of Pyrocumulus Clouds and their Formation

Pyrocumulus cloud
Jose Juan Gutierrez's image for:
"Overview of Pyrocumulus Clouds and their Formation"
Caption: Pyrocumulus cloud
Image by: Jaimito Cartero
© CC-BY-2.0

Pyrocumulus clouds, also known as fire clouds, are formed due to intense heating of atmospheric air on the surface of the ground. The formation of pyrocumulus clouds most commonly occurs during volcanic eruptions or wildfires, but they also can be formed due to industrial pollution. Pyrocumulus clouds are usually formed from between 600 and 900 meters (2,000-3,000 ft.) above the surface of the Earth. This type of cloud can trigger a thunderstorm, producing lightning and increasing the chances of starting a new fire.

What are clouds?

Clouds are dense masses of water droplets and ice crystals suspended in the air. The water droplets and ice crystals condense around small particles of dust, salt, pollen, ice and ashes from volcanic eruptions. Clouds are classified according to the shape they take and their height in the atmosphere. Clouds can be divided into high, middle and low clouds. The basic types of clouds are the heaped cumulus, layered stratus, violent rain nimbus and the wispy cirrus. Different clouds can be described by combining these basic types; for example, cumulonimbus is the term given to clouds that are accompanied by rain, whereas pyrocumulus is the name given to clouds that are formed due to intense heating on the surface of the Earth.

What do they look like?

Pyrocumulus clouds are generally of a grayish or brownish tinge. This is due to the particles of ash and smoke that originate from a fire. Due to the great quantity of ash involved in their formation, pyrocumulus clouds tend to spread out horizontally. The increased condensation of moisture around nuclei particles can induce the formation of a lightning thunderstorm, increasing the danger of starting another fire, especially in forested lanscapes, where the incidences of fire are very common.

How are pyrocumulus clouds formed?

A pyrocumulus cloud can be formed by the transfer of surface heat by convection, causing an air mass to rise up in the presence of moisture in the atmosphere. Forest fires, volcanic eruptions and industrial activity can induce the formation of pyrocumulus clouds. The detonation of a nuclear bomb may produce a pyrocumulus cloud in the form of a mushroom in the sky. The ash from volcanic eruptions, along with ash particles released during combustion and pollution from industrial activity, serve as nuclei around which moisture condenses, forming a pyrocumulus cloud.


Pyrocumulus clouds can start or extinguish a wildfire. On occasion, the moisture that has been condensing around small nuclei particles reaches the dew point and precipitates down as rain. When this occurs, the rain helps extinguish the same fire that created it. On the other hand, if the fire is large enough, the fire may continue to grow, developing into a cumulonimbus cloud or thunderstorm cloud. At the base, a cumulonimbus cloud can be no more than 2,000 ft. above the surface, whereas its top may extend over 39,000 ft. into the tropopause. The great amounts of energy released by cumulonimbus clouds can produce heavy showers and tornadoes.

Clouds have a great influence in the climate of the world. They affect Earth's climate in two ways: The low and middle clouds cool the Earth by reflecting the sun's short-wavelength radiation back into space, whereas high clouds warm the Earth by preventing the longer-wave radiation from escaping from the Earth, producing a greenhouse effect. According to, the smoke from a wildfire, from which pyrocumulus clouds form, can make the sunsets appear redder. This is caused by the diffraction of shorter wavelengths of visible light, such as blue light, and the infiltration of longer wavelengths of visible light, such as red and orange.

More about this author: Jose Juan Gutierrez

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