17th century poison cabinet designed to look like a book
RACETRACK PLAYA MYSTERY SOLVED!!!!!!!!!!!!
Today, a long-awaited paper was published in the open-access journal PLOS One. A team led by a scientist from Scripps institute of oceanography finally observed what no one has seen before; the rocks of Racetrack Playa sliding.
Racetrack playa is a dry lakebed in the northern part of Death Valley. It is distinguished by the features you see here; rocks from one side of the playa have left trails as they somehow slid across to the other side.
There have been a variety of theories for how this happens, including freezing the lake to an icy surface and strong winds, but until last winter no one had ever actually observed it in process, making it a truly great geologic mystery. Using a combination of time lapse cameras and GPS monitoring as seen on the rock in this photo, this team finally, successfully got it last year during winter.
The answer turns out to be that the rocks are actually pushed by ice sheets. Last year, the lake received ~5 cm of precipitation in the form of both rain and snow, enough to cause a thin layer of water above the muddy surface of the lake. During nights with sub-freezing temperatures, this layer of water would freeze. In the morning when it was sunny, the ice would break up into large sheets of ice, only a couple millimeters in thickness, which could be pushed by the wind. Apparently there is even audio of the cracking noises made when these sheets break apart.
Moderate winds on those mornings pushed these sheets of ice up against the rocks, in some cases piling up several ice sheets on the rock until finally there was enough force to make them move.
The ice sheets sometimes break apart against the rocks, explaining how different rocks can be pushed in different directions or why some rocks don’t move while other nearby rocks do.
Mystery solved. A wide, thin sheet of ice, created when the lake has a tiny bit of water in it, cracks apart when the sun reaches it in the morning, and is pushed by the wind, taking the rocks with it.
I put some of the time-lapse video up at our blog a moment ago here:http://the-earth-story.com/post/95927612061/this-is-legit-omg-video-right-here-the-rocks-of
Original paper and image credit:http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0105948
A previous post of ours about Racetrack: