Rock On!

SCIENCE

Some scientists use GPS locations to keep track of wide-ranging sharks. Others attach GPS tags to observe the movements of reclusive snow leopards. And then there are the guys who use the technology to study the movements of rocks. Well, OK. (National Geographic Newswatch)

Use our resources to see how these stones sail!

Discussion Ideas

  • Read through the National Geographic Newswatch article. How do 272-kilogram (600-pound) boulders move across the flat plain of Death Valley’s Racetrack Playa? (What’s a playa? Click here to find out.)
    • Rain collects in a shallow pond in Racetrack Playa. It freezes, creating thin, tiny ice floes. Wind breaks up these ice floes and piles them against the rocks. “This creates enough friction to cause the rocks to skim across the muddy surface of a temporary pond. If you were there to see it, the rocks would look like ice-breaker ships plowing through sea ice—though in this instance, it’s the ice that’s moving the ships.”

 

  • Scientists call the conditions that allow Racetrack Playa’s stones to sail a “Goldilocks phenomenon.” What do they mean by this?
    • Goldilocks, the persnickety blond home invader, would not eat porridge unless the temperature was “just right.” Death Valley’s sailing stones stay put unless the weather conditions at Racetrack Playa are “just right.”
    • The “just right” weather conditions that allow Racetrack Playa’s stones to sail include:
      • precipitation: Death Valley, a desert, has to receive enough rain for a shallow pond to form. (This actually isn’t as unusual as it sounds—read more about deserts in our encyclopedic entry.)
      • temperature: The hottest place on Earth has to be cold enough for water to freeze. (Read about Death Valley and Earth’s other extremes in this GeoStory.)
      • wind: A mild wind needs to be present, to shift the tiny ice floes around the stones.
      • All conditions need to be “just right”: “If the ice is too thick, or the day is too sunny, or the wind isn’t steady enough, then nothing happens,” according to the NG Newswatch article.

 

  • Death Valley National Park warns visitors to Racetrack Playa “The surface of the playa is very fragile. Driving on it or anywhere off established roads is prohibited. Do not move or remove any of the rocks. When the playa is wet, avoid walking in muddy areas and leaving ugly footprints . . . Muddy footprints will disrupt the rocks’ movement and leave unsightly scars for years.” The experiment required fitting 15 rocks with custom-built, motion-activated GPS units and carefully studying their movement. Why do you think the National Park Service allowed scientists to break the rules—removing rocks and walking around the playa?
Scientists have discovered the secret behind the famous "sailing stones" of Death Valley's Racetrack Playa. Photograph by Ricardo Frantz, courtesy Wikimedia. This work has been released into the public domain.

Scientists have discovered the secret behind the famous “sailing stones” of Death Valley’s Racetrack Playa.
Photograph by Ricardo Frantz, courtesy Wikimedia. This work has been released into the public domain.

Note to NG-ineers—you’ve covered critters. This sounds like a job for QuarryCam!

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