Weird Arctic Rock Circles: At Last, an Explanation
By MICHAEL D. LEMONICK
Anyone who has traveled much through the Arctic has seen them:
astonishingly perfect circles, straight-sided polygons, even stripes
that crisscross the hillsides, all made out of stones, as though
some infant giant had been pushing pebbles into pleasing
arrangements. And while nobody has invoked aliens ” the
popular explanation for crop circles in temperate zones ” people
have wondered for centuries what strange force could have
assembled these supernatural-looking formations.
The answer, as two California geologists finally explained in a
paper that appeared in Science last week: it's nothing more
complicated than freezing and thawing ” the same process that
causes roads to buckle in developed parts of the world. According
to lead author Mark Kessler, it all starts with a field strewn
randomly with rocks lying on top of soil. No field is perfectly flat,
of course, and when the soil freezes in winter, any slight bump
expands, pushing the rocks up and to the side. When things thaw
out, though, the bump subsides straight down, so the rocks stay
where they are. Next winter, the bump expands again ” but since
it's wider than it was the first time around, it expands even more,
pushing the rocks further.
Over time, Kessler says ” and computer simulations prove it ”
the rocks, under pressure from expanding bumps on all sides, are
gradually forced into narrow strips that outline broad swaths of
pure soil. At the same time, irregularities in the thickness of the
rock lines are smoothed out by this continuous squeeze. Whether
the final result looks like a circle or a polygon depends on how
thick the initial stone layer is and how much the local soil expands
when it freezes. Stripes turn up when the process happens on a
hillside. No aliens necessary ” and knowing how these
remarkable shapes were formed doesn't take anything away from
their striking beauty.
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