Researchers have found more than 100 craters in the seafloor near Bjørnøya, the southernmost island in the island archipelago of Svalbard. Some of these craters have a diameter of 1000 metres. The craters formed when pockets of gas hydrates exploded out of the seafloor (Illustration: Andreassen et al. 2017).
The
otherwise flat sea floor between the island archipelago of Svalbard
and Finnmark, Norway’s northernmost county, is pocked by massive
craters that were only discovered in the 1990s.
Now,
scientists at the Centre for Arctic Gas Hydrates, Environment and
Climate (CAGE) at UiT - The Arctic University of Norway, have
collected new geophysical data on the craters in the area.
But
instead of finding just a few craters, researchers found hundreds of
them. They range in size from 300 to 1000 metres in diameter. And
they have been blown out of solid bedrock.
Methane
gas blow-outs
The
craters are what remain after a methane gas explosion. Or more
correctly: gas blow-outs.
Methane
gas chambers formed under the seabed during the last ice age. Up
until the end of the ice age they were capped by a kilometres-thick
layer of ice. They have also been kept in place by frozen methane
gas, known as gas hydrates.
When
the ice melted, the gas chambers collapsed one by one. The blow-outs
may have occurred over a couple of days.
But
these blow-outs must have involved enormous forces at the bottom of
the Barents Sea, since the holes have been blasted out of solid
bedrock.
The
researchers in Tromsø expect further blow-outs, as some gas chambers
have not yet blown, and others are slowly building up pressure again.
Mysterious
giant holes in Siberia
Only
a few years ago, reindeer hunters on the Jamal peninsula in
northernmost Siberia also discovered several mysterious giant holes
in the ground.
Russian
scientists eventually determined that the cavities had been filled
with methane gas and subsequently collapsed.
Karin
Andreassen, a professor at UiT, thinks the Russians were correct in
their assessment.
“Methane
gas in Siberia is locked inside the permafrost. And there are frozen
gas hydrates in the Barents Sea that ensure the gas is kept buried in
the seabed,” she says.
Otherwise,
the process is more or less the same, she said. When the permafrost
or gas hydrates thaw, the methane can be released explosively in a
gas blow-out.
Media reports described mysterious giant holes that were found in the tundra several years ago on the Jamal Peninsula in northern Siberia. Additional holes like these have appeared recently. We now know that the holes are likely from methane gas blow-outs, just like the craters that researchers have discovered in the Barents Sea. (Photo: Vasily Bogoyavlensky / AFP / NTB scanpix)
Andreassen
and her colleagues published their results in scientific article in
the journal Science last year that describes the craters in the
seabed north of Norway and how they developed. The picture at the top
of this article is from the article in Science.
Large
blow-outs possible
Andreassen
thinks there will be more large blow-outs in the ocean floor south of
Svalbard, as the seabed becomes warmer and gas-hydrate reservoirs
thaw.
But
she can’t promise that researchers will catch the actual blow-out.
“The
biggest blow-outs in the Barents Sea occurred when the ice melted,
12,000 to 15,000 years ago,” she said.
Andreassen
says there is probably even more methane gas locked in the seabed
around Greenland and in the Arctic Ocean than is found in the Barents
Sea.
That
could lead to some extremely large craters.
Pingos
preceded blow-outs
Researchers
have now examined satellite images of northern Siberian from a few
years back and looked at the area where the explosions occurred. They
found that the year before the huge crater appeared, there were large
pingos in the same place.
Pingos
are found in the arctic and are usually raised hills, like a giant
pimple, with a core of ice.
In
this case, however, the pingos must have been filled with gas in the
form of ice, bound up with water in gas hydrates and permafrost.
Russian
scientists have now mapped 7,000 gas-filled pingos that are poking
through the thawing permafrost, visible in satellite images that
illustrate how the pingos form and grow, published in The Siberian
Times.
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