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Ever since last July, when a Russian YouTube user uploaded “Giant Hole in the Ground,”
a thirty-four-second video of, well, a giant hole in the ground—about
two hundred and fifty feet across and more than a hundred and fifty feet
deep—the world has been fascinated by a group of mysterious craters in
the tundra of the Russian Arctic. On Thursday, Vasily Bogoyavlensky, the
deputy director of the Oil and Gas Research Institute, at the Russian
Academy of Sciences, told Agence France-Presse that
he and his colleagues have now identified seven of these “holes at the
end of the world,” including one that is more than half a mile across.
“But, in fact, there are plenty more,” Bogoyavlensky said.
Theories
about the mystery craters have variously attributed them to meteorite
impacts, missile strikes, explosions from nearby gas fields, and the
melting of soil-covered ice mounds, known as pingos. The most likely
explanation for the phenomenon, however, seems to be climate change.
Underground temperatures in parts of Siberia have risen by nearly four degrees in
the past fifteen years. As the ground there—mostly permafrost—warms, it
releases methane. The methane builds up until there’s an explosion,
which leaves behind a hole. “The phenomenon is similar to the eruption
of a volcano,” Bogoyavlensky said.
Whether or not
they end in explosions, these methane releases are a serious concern.
Methane is a greenhouse gas, and on a molecule-by-molecule basis it is a
far more potent warming agent than carbon dioxide (although it doesn’t
last as long in the atmosphere). If the permafrost is leaking methane
because of rising temperatures, a positive-feedback loop could be taking
effect: more methane leads to further warming, which leads to further
thawing, and so on.
But the holes in Siberia
also point to another, stranger phenomenon. Global warming and geology
turn out to be connected in unexpected ways. Consider, for example,
earthquakes. Generally, earthquakes occur because of the movements of
Earth’s tectonic plates; they tend to take place along plate boundaries.
But recently Greenland has been experiencing an unusually large number of quakes. One
widely discussed theory attributes this to the shrinking of the
Greenland ice sheet. As the ice sheet melts, its weight declines,
allowing the land underneath it to rise. The process, which is known as
isostatic rebound, may well be responsible for the increase in seismic
activity.
Iceland, too, is rising, and for
similar reasons. As the country’s glaciers melt, the land is rebounding.
A recent study showed that some parts of the country are gaining
elevation at the astonishing rate of 1.4 inches a year. “What we’re
observing is a climatically induced change in the earth’s surface,”
Richard Bennett, one of the authors of the study and a geoscientist at
the University of Arizona, told the Web site Live Science last
month. In the case of Iceland, that change may lead to an increase in
volcanic activity. As the land rises, the pressure on the rock beneath
it changes. Lower pressure translates into a lower melting temperature,
which could, in turn, translate into more (or at least more destructive)
volcanic eruptions. The past five years have been packed with
“interesting volcanic activity,” Sigrún Hreinsdóttir, Bennett’s
fellow-researcher and a geophysicist at the University of Iceland, told the Washington Post. “You
can’t make any statistics from those few data points, of course, but
you do notice there might be a connection with the uplift,” And there’s a
precedent: during the deglaciation that occurred at the end of the last
ice age, some twelve thousand years ago, volcanic activity in Iceland
is estimated to have increased by as much as a factor of thirty.
In
Siberia, the enormous craters are rapidly filling with water. Soon,
they’ll probably be lakes. Of course, by then, new craters may well have
opened up, and with them new mysteries to investigate in a warming
world.
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