June 01, 2017
The Siberian craters are small in comparison to these giant methane
"monsters" that have been discovered on the Arctic Sea floor.
Methane, a potent greenhouse gas is
still leaking in large amounts from the enormous craters that formed
about 12,000 years ago.
The Barents Sea,
the team found and studied the craters.
"The crater area was
covered by a thick ice sheet during the last ice age, much as
West Antarctica is today. As climate warmed, and the ice sheet
collapsed, enormous amounts of methane were abruptly released.
This created massive
craters that are still actively seeping methane" says Karin
Andreassen, first author of the study (Massive
Blow-Out Craters formed by Hydrate-controlled Methane expulsion
from the Arctic Seafloor) and professor at
CAGE 'Centre for Arctic Gas
Hydrate, Environment and Climate.'
Over 100 of the
Methane Craters Are Up To One Kilometer Wide
A few of these craters were first observed in the 90-ties.
However, using new
researchers were able to discover that the craters cover a much
larger area than previously thought. Over one hundred of the methane
craters are up to one kilometer wide.
In comparison, the huge blow-out craters on land on the Siberian
Gydan are 50-90 meters wide, but
similar processes may have been involved in their formation.
sinkhole in Siberia
The new Yamal crater is in the area's Taz district
the village of Antipayuta and has
diameter of about 49ft (15 meters).
The Arctic ocean floor hosts vast amounts of methane trapped as
hydrates, which are ice-like, solid
mixtures of gas and water.
These hydrates are stable under high pressure and cold temperatures.
The ice sheet provides perfect conditions for subglacial gas hydrate
formation, in the past as well as today.
Today more than 600 gas flares are identified in and around these
craters, releasing the greenhouse gas steadily into the water
column. Researchers say it's nothing compared to the blow-outs of
the greenhouse gas that followed the deglaciation.
The amounts of methane
that were released must have been quite impressive.
There are several hundred craters
area the study looked at.
one hundred of them
to 1,000 meters wide.
Some 2000 meters of ice loaded what now is ocean floor with heavy
weight. Under the ice, methane gas from deeper hydrocarbon
reservoirs moved upward, but could not escape.
It was stored as gas
hydrate in the sediment, constantly fed by gas from below, creating
"As the ice sheet
rapidly retreated, the hydrates concentrated in mounds, and
eventually started to melt, expand and cause over-pressure.
The principle is the
same as in a pressure cooker:
if you do not
control the release of the pressure, it will continue to
build up until there is a disaster in your kitchen.
These mounds were
over-pressured for thousands of years, and then the lid came
They just collapsed
releasing methane into the water column" says Andreassen.
Processes Are Ongoing Under Ice Sheets Today
Major methane venting events such as this appear to be rare, and may
therefore easily be overlooked.
The massive craters were formed around 12,000 years ago,
still seeping methane and other gases.
Andreia Plaza Faverola/CAGE
infrequency, the impact of such blow-outs may still be greater
than impact from slow and gradual seepage.
It remains to be seen
whether such abrupt and massive methane release could have
reached the atmosphere. We do estimate that an area of
hydrocarbon reserves twice the size of Russia was directly
influenced by ice sheets during past glaciation.
This means that a
much larger area may have had similar abrupt gas releases in the
overlapping time period" says Andreassen
Another fact to consider
is that there are reserves of hydrocarbons beneath the load of West
Antarctica and Greenland ice sheets today.
"Our study provides
the scientific community with a good past analogue for what may
happen to future methane releases in front of contemporary,
retreating ice sheets" concludes Andreassen.