COURTESY BOOTLEG FIRE INCIDENT COMMAND
In this photo taken with a drone, a pyrocumulus cloud, also known as a fire cloud, is seen over the Bootleg Fire in southern Oregon on Wednesday. Smoke and heat from a massive wildfire in southeastern Oregon are creating "fire clouds" over the blaze — dangerous columns of smoke and ash that can reach up to 30,000 feet (9,144 meters) and are visible for more than 100 miles (160 kilometers) away. Authorities have put these clouds at the top of the list of the extreme fire behavior they are seeing on the Bootleg Fire, the largest wildfire burning in the U.S.