A fierce blaze that has burned along the Grand Canyon's North Rim since being sparked by lightning on July 4 has exploded in size in recent days, reaching "megafire" status and becoming the largest wildfire in the U.S. this year, according to the Arizona Republic.

A wildfire in northern Arizona has grown thousands of acres in just a few days as firefighters continue to work to regain containment.

Both it and the Monroe Fire, burning further north near Monroe, Utah, are generating pyrocumulus clouds — sometimes called "fire clouds" — that form when air over a fire becomes superheated and rises in large, smoky columns. The massive clouds are visible for hundreds of miles and resemble the shape of an anvil.