One of the most breathtaking views in North America got a bit more breathtaking last week.
The Grand Canyon in Colorado was slowly filled with a thick layer of cloud last Thursday after warm air at the top of the deep ravine prevented the colder air at the bottom from rising.
Such a "weather event" is known as a "total temperature inversion" and it usually only occurs at the Canyon, which receives around five million visitors a year, once every several years. It last happened in December 2013.
As the air at the bottom cools, dew caused by rain turns into fog rises to the rim of the Canyon, which stops the air from escaping.
A time-lapse video from the Grand Canyon National Park shows thick fog and cloud rolling across the top of the Canyon, at times making it impossible to see anything, before a breeze blows a top layer away to reveal the spectacular sight.
Because the Grand Canyon is so huge (277 miles and 6,000 feet deep at its deepest point), it could take days for the clouds to clear from the ravines, according to the National Park Service.
Watch another video time-lapse of the event below:Reuse content