Visitors and experts alike have long been puzzled by the sight of boulder tracks criss-crossing a dusty bowl known as the Racetrack Playa in Death Valley National Park, California.

Now two researchers say the rocks, which can sometimes be heavy and large, are propelled along by thin, clear sheets of ice on breezy, sunny days. They call it "ice shove".

In a place where rainfall are almost non-existent, rocks are being shoved around by mechanisms typically seen in arctic climes.

The findings are based on a lucky accident by the two researchers while they were studying the sliding rock phenomenon. They actually witnessed the boulders moving in December when they went to check their time-lapse cameras in the valley.