Sailing Stones
Sailing stones,
also known as moving rocks are a
geological phenomenon where rocks move and inscribe long tracks along a smooth
valley floor without human or animal invention. This moving rocks have been
observed and studied in various locations, including Little Bonnie Claire Playa
in Nevada and most famously at racetrack Playa, Death Valley National Park,
California. Where the number and length of tracks are notable
Stones with rough
bottoms leave straight striated tracks, while those with smooth bottoms tend to
wander. Stones sometimes turn over, exposing another edge to the ground and
leaving a different track in the stone’s wake.
Trails differ in
both direction and length. Rocks that start next to each other may travel
parallel for a time, before one abruptly changes direction to the left, right,
or even back to the direction from which it came. Trail length also varies two
similarly sized and shaped rocks may trafel uniformly, then one could move
ahead or stop in its track.
At racetrack
playa, these tracks have been studied since the early 1900s, yet the origins of
stone movement were non confirmed and remainded the subject of research fpr
which several hypotheses existed. However, as of august 2014, timelapse video
footage of rocks moving has been published, showing the rocks moving at hight
wind within the flow of thin melting sheets of ice. The scientists have thus
identified the cause of the moving stones to be ice chove.
News articles
reported the mystery solved when researchers observed rock movements using GPS
and time-lapse photography. The research team witnessed and documented rock
movement on December 20, 2013, that involved more than 60 rocks, with some
rocks moving up to 224 m between December 2013 and january 2014 in multiple
movements events. These observations contradicted earlier hypotheses of winds
of thick ice floating rocks off the surface. Instead, rocks move when large ice
sheets a few millimeters thick floating in a ephemeral winter ponf start to
break up during sunny days. These thin floating ice panels, frozen during cold
winter nights, are driven by light winds and shove rocks at up to 0,3 km/ h.
Some gps measured moves lasted up to 16 minutes, and a number of stones moved
more than five times during the existence of the playa pond in the winter.
The movement of
the rocks results when large ice sheets a few millimeters thick floating in a
ephemeral winter pond start to break up during sunny days. Frozen during cold
winter nights, these thin floating ice panels are driven by wind and shove
rocks at speeds up to 5 meters per minute.
A balance of very
specific conditions is throught to be needed for stones to move :
-a flooded
surface
-a thin layer of
clay
-ice floes
-warming
temperatures causing ice breakup
Sumber:
https://en.wikipedia.org/wiki/Sailing_stones-wind
