For decades, scientists have been unable to explain what caused 'sailing stones' on Racetrack Playa in Death Valley National Park to move up to hundreds of metres - until now.
Located in California, the phenomenon sees rocks weighing more than 300 kilograms move along the park's flat desert basin and leaving long trails.
Without an explanation for the mysterious movements, theories such strong winter winds of up to 144 kmph coupled rain causing the clay to become slippery were citied as possible reasons for the 'sailing stones'.
Other theories included ice sheets carrying the rocks or even ice forming around the stones helping them move with the wind.
Yet after years of speculation, scientists claim to have conclusively solved the puzzle, with research results published this week, reported GrindTV.
- New invention creates Kickstarter record
- Shaun the sheep shorn, but fleece fails to break world's woolliest record
A research team, led by paleobiologist Richard Norris of Scripps Institution of Oceanography, University of California, San Diego, concluded the trails left by the stones are a result of thick sheets of ice forcing the rocks across the desert basin under certain conditions.
While the theory was dismissed following tests in 1976, researchers were able to prove it using custom built motion-activated GPS units.
The units were put into 15 rocks placed on the playa in the winter of 2011, with permission from the National Park Service.
As part of the Slithering Stones Research Initiative, the team expected it would take between five and 10 years before there was any movement.
While Ralph Lorenz, one of the paper’s authors, called it "the most boring experiment ever", on December 21, 2013, the team got a major breakthrough.
"Science sometimes has an element of luck," Richard Norris said. "Only two years into the project, we just happened to be there at the right time to see it happen in person."
"(The) ice breakup happened just around noon, with popping and cracking sounds coming from all over the frozen pond surface," he said.
Shortly after the team had arrived at the playa, three inches of water fell and the rocks started to move.
This helped the researchers determine the rare combination of events required to enable the rocks to move across the basin.
In order for the stones to 'sail' the playa needs to fill with water deep enough to create floating ice but shallow enough for the rocks to protrude during cold winter nights.
As the temperatures fall over night, the water in the basin freezes to create thick sheets of ice known as 'windowpanes'.
At sunrise, as the ice starts melting, it fragments into big floating sections and light winds allow these panes of ice to push the rocks in front of them.
As a result, the stones leave trails in the mud below and these become evident when the basin dries in warmer months.
The rocks in the playa were pushed a few inches per second by quarter-inch sections of ice in winds of about 16 kmph.
Lorenz said a previous movement was believed to have happened in 2006, meaning the rocks move about one millionth of the time.
He added that evidence indicates that due to climate change, the frequency the rock movement has fallen since the '70s.
Richard Norris' cousin Jim Norris works with an engineering firm and said it is possible tourists have seen the rocks being pushed without realising it. "It is really tough to gauge that a rock is in motion if all the rocks around it are also moving," Jim Norris said.
While documenting hundreds of rocks moving in five separate events over two-and-a-half months, Richard Norris said it showed the power of ice in rock motion.
"But we have not seen the really big boys move out there... Does that work the same way?," he said.
Morning news break – August 29