A beautiful and somewhat rare phenomenon has graced the Grand Canyon for the second time this winter.

A sea of fog filled the canyon on Thursday, flowing through the rock formations that tower above the Colorado River. Battleship Rock on the South Rim (seen below) “truly looked like a ship today, cutting through the waves,” said the Interior Department.

The fog is formed by a total cloud inversion, which occurs when cold air is trapped in the canyon and topped by a layer of warm air. If the moisture in the cold pool is sufficient, condensation will occur and fog will form.

“While typically a rare event, this is the second cloud inversion at the Grand Canyon in six weeks,” said the Interior Department.

These total inversions are actually a rare event, according to the National Weather Service, who says that the phenomenon typically happens just once every several years. The previous total cloud inversion was in mid-December.