Mysterious Siberian crater attributed to methane
Build-up and release of gas from thawing permafrost most
probable explanation, says Russian team.
By Katia Moskvitch in Nature Magazine
The crater in the Yamal peninsula in
Siberia is 30-metres wide.
A mystery crater spotted in the
frozen Yamal peninsula in Siberia earlier this month was probably caused by
methane released as permafrost thawed, researchers in Russia say.
Air near the bottom of the crater
contained unusually high concentrations of methane — up to 9.6% — in tests
conducted at the site on 16 July, says Andrei Plekhanov, an archaeologist at
the Scientific Centre of Arctic Studies in Salekhard, Russia. Plekhanov, who
led an expedition to the crater, says that air normally contains just 0.000179%
methane.
Since the hole was spotted in
mid-July by a helicopter pilot, conjecture has abounded about how the
30-metre-wide crater was formed — a gas or missile explosion, a meteorite
impact and alien involvement have all been suggested.
But Plekhanov and his team believe
that it is linked to the abnormally hot Yamal summers of 2012 and 2013, which
were warmer than usual by an average of about 5°C. As temperatures rose, the
researchers suggest, permafrost thawed and collapsed, releasing methane that had
been trapped in the icy ground.
Other researchers argue that
long-term global warming might be to blame — and that a slow and steady thaw in
the region could have been enough to free a burst of methane and create such a
big crater. Over the past 20 years, permafrost at a depth of 20 metres has
warmed by about 2°C, driven by rising air temperatures1, notes
Hans-Wolfgang Hubberten, a geochemist at the Alfred Wegener Institute in
Potsdam, Germany.
Hubberten speculates that a thick
layer of ice on top of the soil at the Yamal crater site trapped methane released
by thawing permafrost. “Gas pressure increased until it was high enough to
push away the overlying layers in a powerful injection, forming the crater,” he
says. Hubberten says that he has never before seen a crater similar to the
Yamal crater in the Arctic.
Larry Hinzman, a permafrost
hydrologist at the University of Alaska in Fairbanks and director of the
International Arctic Research Center, says that such craters could become more
common in permafrost areas as the region heats up.
In Siberian permafrost, large
deposits of methane gas are trapped in ice, forming what is called a gas
hydrate. Methane remains stable and frozen at certain temperatures, but as the
permafrost warms, and its internal strength decreases, it may be less able to
withhold the build-up of sub-surface gases, he says, leading to a release.
But such gas hydrates normally occur
at depths of at least 100 metres, says Carolyn Ruppel, a geophysicist in charge
of the gas hydrates project at the US Geological Survey in Woods Hole, Massachusetts.
The depth of the Siberian crater is not known. When Plekhanov and his team
tried to measure its depth with a video camera tied to a 50-metre rope, the
camera did not reach the bottom. But the video footage suggests that the depth
to a pool of water at the bottom of the crater is around 70 metres, Plekhanov
says. The water could add considerably to that dry depth, he adds.
To confirm what caused the crater,
Plekhanov says that another visit is needed to check the methane concentration
in air trapped in its walls. That will be difficult, however: “Its rims are
slowly melting and falling into the crater,” Plekhanov says. “You can hear the
ground falling, you can hear the water running, it’s rather spooky.”
Since the crater was reported, local
reindeer herders have noted a similar but smaller hole nearby. Although the
hole is yet to be confirmed, scientists worry that the release of trapped
methane could threaten local industry and communities. “If [a release] happens
at the Bovanenkovskoye gas field that is only 30 km away, it could lead to an
accident, and the same if it happens in a village,” says Plekhanov.
To avoid such an event, researchers
have now suggested drilling holes into the permafrost. “If one knew where the
build-up was, it might be possible to release the pressure, and maybe even use
the gas,” says Hinzman.
- Romanovsky, V. E., Smith, S. L. & Christiansen, H.
H. Permafrost Periglac. 21, 106–116 (2010).
The original article with an image of the crater can be
found at: http://www.nature.com/news/mysterious-siberian-crater-attributed-to-methane-1.15649
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