Regarded by many as one of the seven natural wonders of the world, tourists travel from around the globe to take in the breathtaking view from edge of the Grand Canyon. 
 
 Usually they can see for miles, gazing out across the 18miles-wide valley carved out by the Colorado River 17 million years ago - but not today. 
 
 A rare weather phenomenon has caused a thick sea of fog to rise from the foot of the canyon, sitting just yards from the top of the surface, creating an eerily beautiful effect. 
 
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 A thick blanket of fog rose from the foot of the Grand Canyon, creating an eerily beautiful effect for thousands of tourists visiting the breathtaking Arizona valley 
 
 Photographer gather to take a picture of the clouded view, caused by a unique phenomenon called a total 'temperature inversion' 
 
 Hikers and photographers gathered to take in the view, which was, if anything, even more spectacular than usual. 
 
 In scenes only usually seen when flying or from the top of world's tallest mountains, the Grand Canyon appears to be sitting on top of the clouds. 
 
 The rare weather system, which only happens about once every several years, has been caused by recent rains in northern Arizona. 
 
 Warm air at the top of the canyon stops the colder air at the bottom of the valley from rising, stopping the two masses of air from mixing. 
 
 As the chillier air cools, dew caused by earlier the rain, which has now turned into fog, rises to the rim of the canyon, where the warmer air stops it from escaping. 
 
 This is known as a 'total temperature inversion' and only takes place at the canyon once every several years. 
 
 In scenes usually seen when flying or from the top of world's tallest mountains, the Grand Canyon appears to be sitting on top of the clouds 
 
 A couple watch a sunset at the Grand Canyon, where the spectacular view was today blocked by a thick layer of cloud cause by a rare weather system 
 
 Despite the event only taking place around once a decade, tourists were treated to a similarly mesmerising sight at the Grand Canyon last year. 
 
 The thick clouds are expected to linger in the canyon today, eventually clearing over the weekend as warmer weather returns, according to the National Weather Service. 
 
 When the fog gathered this time last year, Grand Canyon park ranger Erin Whittaker told MailOnline that some of the tourists visiting the canyon were disappointed they couldn't see the Colorado River below, and just figured it was a normal weather pattern. 
 
 But she and the other rangers tried to explain just how lucky they were to see the cloud-covered canyon, as locals turned out photograph the stunning view. 
 
 'Word spread like wildfire and most ran to the rim to photograph it. What a fantastic treat for all!' Ranger Whittaker said. 

 GRAND CANYON NATIONAL PARK, Ariz. (AP) — A rare weather phenomenon at the Grand Canyon had visitors looking out on a sea of thick clouds just below the rim. 
 
 In this photo provided by the National Park Service, visitors to Mather Point on the South Rim of Grand Canyon National Park, in Ariz., view a rare weather phenomenon - a sea of thick clouds filling the... (Associated Press) 
 
 This photo provided by the National Park Service shows dense clouds at the south rim of the Grand Canyon on Thursday, Dec. 11, 2014 in Arizona. A rare weather phenomenon on Thursday had visitors looking... (Associated Press) 
 
 This photo provided by the National Park Service shows dense clouds at the south rim of the Grand Canyon on Thursday, Dec. 11, 2014 in Arizona. A rare weather phenomenon on Thursday had visitors looking... (Associated Press) 
 
 The total cloud inversion is expected to hang inside the canyon throughout Thursday. 
 
 Cory Mottice of the National Weather Service says the weather event happens about once every several years, though the landmark was treated to one last year. 
 
 The fog that has been shrouding parts of northern Arizona is courtesy of recent rains. Mottice says the fog is able to stick around and built up in the Grand Canyon overnight when there is no wind. 
 
 With an inversion, the clouds are forced down by warm air and unable to rise. 
 
 Mottice says the Grand Canyon gradually will clear up in the coming days.
– Yesterday's visitors to the Grand Canyon missed seeing its great depths, but perhaps witnessed something even more awe-inspiring. Due to a rare weather event known as a total cloud inversion, the canyon filled nearly to the brim with a sea of clouds—a result of warm air forcing clouds down into the canyon where wind can't whisk them away, the AP reports. The Daily Mail notes that as a result of the phenomenon, which occurs every few years, "the Grand Canyon appears to be sitting on top of the clouds." The National Weather Service expects the clouds to clear out over the weekend.