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Friday, June 12, 2020

Malin Waage et al. (2020) -- Giant, methane gushing craters on floor of Barents Sea

Malin Waage et al, 

Geological controls 
of giant crater development 
on the Arctic seafloor.

2020

Scientific Reports

DOI: 10.1038/s41598-020-65018-9



SUMMARY:
The craters are up to 
one kilometer wide 
and 35 meters deep. 

They are leaking methane. 

Exploration of petroleum
resources in the Barents Sea 
is a hot topic in Norway.

The area is a part of 
a vulnerable Arctic 
ecosystem. 

But the area's geological 
system is poorly understood.

A recent study 
in Scientific Reports 
looked beneath these 
craters in the ocean floor 
and revealed the 
geological structures.

"It turns out that this area 
has a very old fault system—
essentially, cracks in bedrock 
that likely formed 250 million 
years ago," says Malin Waage, 
a postdoc at CAGE, Centre for 
Arctic Gas Hydrate, Environment 
and Climate, and the first author 
of the study. 

The deep origin of craters 
and mounds was discovered 
using cutting edge 3-D 
seismic technology that can 
penetrate deep into the
ocean floor and help scientists 
visualize the structures 
in the hard bedrock 
underneath.

250-million-year-old cracks 
in the seafloor feed greenhouse 
gas methane into giant craters 
in the Barents Sea. 

More than 100 craters 
are found in the area. 

"Our 3-D survey covered 
approximately 20 percent 
of the entire crater area. 

We believe that it is important 
to understand if similar fault 
systems exist in the larger 
context of the Barents Sea, 
because they potentially 
could pose a threat 
to marine operations."

"There is still very much 
that we don't know about 
this system. 

But we are currently 
collecting and 
analyzing 
new data in the 
Barents Sea, 
which is 
dominated 
by similar 
crater structures. 

This can help us map 
in greater detail the 
fault systems and 
associated 
weakness," 
says Waage.



The oil industry 
needs to know:
(1)
Will these weak structures 
lead to unpredictable and 
explosive methane release ? 

(2)
Can such a release 
be triggered by
drilling for oil. ?

(3)
Will the methane gas 
reach the atmosphere 
and cause greenhouse 
warming ?



DETAILS:
A 2017 study, in  PNAS, 
mapped several methane 
mounds, some 500 meters 
wide, in the Barents Sea. 

The mounds 
were considered 
to be signs of 
impending methane 
expulsions that 
created the craters.

Another 2017 study, 
published in Science, 
described hundreds
of massive, kilometer-
wide craters on the 
ocean floor in the 
Barents Sea. 


Now, more than 600 
gas flares were identified 
in and around these craters, 
releasing the greenhouse 
gas steadily into the water.


Malin Waage also said: 
"Craters and mounds appear 
along different fault structures 
in this system. 

These structures control 
the size, placement and 
shape of the craters. 

The methane that is leaking 
through the seafloor originates 
from these deep structures 
and is coming up through t
hese cracks."

"Our previous studies 
in the area hypothesized
that climate warming 
and the retreat of 
the ice sheet some 
20,000 years ago caused 
the gas hydrates beneath 
the ice to melt, leading to 
abrupt methane release 
and creating craters," 
said Waage.

Gas hydrates are a 
solid form of methane 
that is stable in 
the cold temperatures 
and high pressure 
that an enormous 
ice sheet provides. 

As the ocean warmed up, 
and the pressure of the ice 
sheet lifted, the methane ice 
in the seafloor melted, 
and the craters formed.

"This study, however, 
adds several layers 
to that picture, 
as we now see 
that there has been 
a structural weakness 
beneath these giant 
craters for much longer 
than the last 20,000 years. 

Deep below the seafloor, 
the expansion of gas 
and release of water 
built up a muddy slurry 
that eventually erupted 
through the fractures 
and caused seafloor 
collapses and craters 
in the hard bedrock. 

Think of it as a building: 
The roof of a building 
can cave in if the ground 
structure is weak. 

We believe that this 
is what happened 
in the crater area after 
the last glaciation,"  
says Waage.