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.

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.

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