Have you heard of the sailing stones?
One of the strangest natural phenomena ever identified, these are dolomite and syenite rocks around 8-17 kg that rest on the flat, barren lakebed known as the “racetrack” in Death Valley. And move. Yes, that’s right. They move. And they leave skidmarks behind them.
Different rocks even move in different ways. Lighter ones move more. Rough-bottomed rocks move in straight lines, whilst smooth ones wander.
The mystery has bewitched researchers and the public alike since the early 1900s. The movements are rare, and no one had been able to observe them and so identify the cause – until December 2013.
One of the strangest natural phenomena ever identified, these are dolomite and syenite rocks around 8-17 kg that rest on the flat, barren lakebed known as the “racetrack” in Death Valley. And move. Yes, that’s right. They move. And they leave skidmarks behind them.
Different rocks even move in different ways. Lighter ones move more. Rough-bottomed rocks move in straight lines, whilst smooth ones wander.
The mystery has bewitched researchers and the public alike since the early 1900s. The movements are rare, and no one had been able to observe them and so identify the cause – until December 2013.
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| A sailing stone in Death Valley. By Lgcharlot - via Wikipedia Commons. |
Dubbed “the most boring experiment ever”, the team of US researchers strapped video and timelapse cameras and GPS trackers to a bunch of rocks... and waited.
And in December 2013, they watched as over a dozen rocks travelled[1]. At the start of the month, over 16 minutes, some moved around 70 m, and just before Christmas, another moved 40 m in 12 minutes – leaving their trails behind them. The speed was estimated at 2-6 cm/s.
How did it happen?
It turns out the sailing stones only sail under the specific conditions of this environment. The racetrack is exceptionally flat, and exceptionally dry (with temperatures as high as 56.7oC). But when it does get cold and wet – but not too cold and wet – a thin layer of water forms on the hard surface, unable to penetrate, and, overnight, freezes into a thin layer of ice. And this ice is instrumental to the movement of the sailing stones.
Why?
In the morning, the ice breaks into sheets. And, if the wind is at just the right speed (around 7-10 mph), it shoves the ice sheets and sailing stones around before they melt completely, leaving trails in the earth. As the ice fractures and thins, some rocks stop moving, and that’s why some of them move whilst others do not.
It’s a fascinating phenomenon to watch (and you can do so in various places!) – and a satisfying conclusion to a scientific mystery. Which will be next?
Check out our site for more Things We Don’t Know that haven’t been solved, and look out for updates from researchers working on these mysteries now!
And in December 2013, they watched as over a dozen rocks travelled[1]. At the start of the month, over 16 minutes, some moved around 70 m, and just before Christmas, another moved 40 m in 12 minutes – leaving their trails behind them. The speed was estimated at 2-6 cm/s.
How did it happen?
It turns out the sailing stones only sail under the specific conditions of this environment. The racetrack is exceptionally flat, and exceptionally dry (with temperatures as high as 56.7oC). But when it does get cold and wet – but not too cold and wet – a thin layer of water forms on the hard surface, unable to penetrate, and, overnight, freezes into a thin layer of ice. And this ice is instrumental to the movement of the sailing stones.
Why?
In the morning, the ice breaks into sheets. And, if the wind is at just the right speed (around 7-10 mph), it shoves the ice sheets and sailing stones around before they melt completely, leaving trails in the earth. As the ice fractures and thins, some rocks stop moving, and that’s why some of them move whilst others do not.
It’s a fascinating phenomenon to watch (and you can do so in various places!) – and a satisfying conclusion to a scientific mystery. Which will be next?
Check out our site for more Things We Don’t Know that haven’t been solved, and look out for updates from researchers working on these mysteries now!
why don't all references have links?
[1] Lorenz, R. D., Norris, J. M., Jackson, B. K., Norris, R. D., Chadbourne, J. W., and Ray, J.: Trail formation by ice-shoved "sailing stones" observed at Racetrack Playa, Death Valley National Park, Earth Surf. Dynam. Discuss., 2, 1005–1022, https://doi.org/10.5194/esurfd-2-1005-2014, 2014.
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