In July last year, a lightning strike at the North Rim of the Grand Canyon, Arizona, US sparked the Dragon Bravo Fire, a major wildfire that was one of the largest in the state’s history. While helping fight the blaze, a friend of Andrew Brischke (Member 65,404) spotted this immense cloud towering above the canyon rim.

This is a pyrocumulus cloud, more formally a Cumulus congestus flammagenitus, with the flammagenitus term indicating a cloud generated by fire. Intense heat from fires like Dragon Bravo drives powerful convection currents upward. Combustion also releases water vapour as well as soot particles that act as seeds on which cloud droplets can form as the rising air cools. The result is a towering, smoke-laden, brownish cloud that few, even in the Cloud Appreciation Society, would welcome overhead.