fire clouds
Fire clouds over CaliforniaJames Haseltine/Nasa

Photos of a huge 'fire cloud' above California, where wildfires have been burning for days, have been captured by an F-15C fighter jet.

Earlier this week, California declared a state of emergency following one of the "most severe droughts on record".

Wildfires broke out at the start of the month, with fires spreading across forests and grasslands, leaving over 100,000 acres charred in just a few days.

Capturing the extent of the damage, satellite images from Nasa's Terra satellite show the evolution and rapid expansion of the fires: "Many areas of active burning expanded significantly between the satellite overpasses, as smoke plumes blossomed into towering pyrocumulus clouds," Nasa said.

fire clouds
California declared a state of emergency earlier this week as the state experiences one of the worst droughts on recordJames Haseltine/Nasa

Pyrocumulus clouds are often referred to as fire clouds. They are tall, cauliflower-shaped clouds and appear as opaque white patches hovering over darker smoke.

"Pyrocumulus clouds are similar to cumulus clouds, but the heat that forces the air to rise (which leads to cooling and condensation of water vapor) comes from fire instead of sun-warmed ground. Under certain circumstances, pyrocumulus clouds can produce full-fledged thunderstorms, making them pyrocumulonimbus clouds."

fire clouds
Fire clouds and wildfires seen from spaceNasa

Close up images of the huge fire clouds were captured from an F-15C Eagle fighter and show developing fire clouds above the Oregon Gulch fire, which is one part of the Beaver Complex fire.

Experts monitor the fire clouds closely, as they can inject smoke and pollutants into the atmosphere, affecting air quality over a large area: "In this case, the outburst of pyrocumulus activity lofted a large amount of smoke high into the atmosphere, and winds pushed it north and east over Oregon.

"On 3 August 2014, the Ozone Mapping Profiler Suite, on the Suomi NPP satellite, detected the smoke as it passed over Oregon and drifted toward Idaho and Montana."