It is certainly large but significance may be another matter. A mile
deep is impressive, yet is only five thousand feet which describes
every mountain range anyway. Besides the weight of ice has driven
the floor downward. Nothing is said regarding how long the structure
may be, nor if there is related volcanism. Both have a huge impact
on importance geologically.
Otherwise we are slowly mapping the real surface of the Antarctic and
that is interesting anyway.
This is part of a long process that is clearly well underway.
Antarctic: Grand
Canyon-sized rift 'speeding ice melt'
By Richard Black
Environment
correspondent, BBC
25 July 2012 Last
updated at 13:11 ET
A rift in the Antarctic rock as deep as the Grand Canyon is
increasing ice melt from the continent, researchers say.
A UK team found the
Ferrigno rift using ice-penetrating radar, and showed it to be about
1.5km (1 mile) deep.
Antarctica is home to
a geological rift system where new crust is being formed, meaning the
eastern and western halves of the continent are slowly separating.
The team writes in
Nature journal that the canyon is bringing more warm sea water to the
ice sheet, hastening melt.
The Ferrigno rift lies
close to the Pine Island Glacier where Nasa scientists found a giant
crack last year; but the newly discovered feature is not thought to
be influencing the "Pig", as it is known.
The rift lies beneath
the Ferrigno Ice Stream on a stretch of coast so remote that it has
only been visited once previously.
The British Antarctic Survey (BAS) project revisited the area two
years ago in the person of Aberdeen University glaciologist Robert
Bingham.
The plan was to make
ground observations that could link to the satellite data showing
unexpectedly pronounced ice loss from the area.
The team towed
ice-penetrating radar kit behind a snowmobile, traversing a total of
about 2,500km (1,500 miles).
"What we found is
that lying beneath the ice there is a large valley, parts of which
are approximately a mile deeper than the surrounding landscape,"
said Dr Bingham.
\
"If you stripped
away all of the ice here today, you'd see a feature every bit as
dramatic as the huge rift valleys you see in Africa and in size as
significant as the [US] Grand Canyon.
"This is at odds
with the flat ice surface that we were driving across - without these
measurements we would never have known it was there."
###
The shape of the rift
is shown in a radar cross-section of ice and underlying rock
The Ferrigno rift
extends into a seabed trough, called Belgica.
The scientists suggest
that during Ice Ages, when sea levels were much lower than at
present, the rift would have channelled a major ice stream through
the trough.
Now, they suggest, the
roles are reversed, with the walls of the Belgica trough channelling
relatively warm sea water back to the ice edge.
Penetrating between
the Antarctic bedrock and the ice that lies on it and lubricating the
join, the water allows ice to flow faster into the sea.
"We know that the
ice loss from the West Antarctic Ice Sheet is governed by delivery of
warm water, and that the warm water is coming along channels that
were previously scoured by glaciers," said Prof David Vaughan of
BAS.
"So the geology
and the present rate of ice loss are intricately linked, and they
feed back - if you have fast-flowing ice, that delivers ice to the
edge where it can be impacted by warm water, and warm water makes the
ice flow faster," he told BBC News.
Prof Vaughan doubted
there would be more such features around the West Antarctic coast,
though in the remoter still regions of the east, it was a
possibility.
Ice loss from West
Antarctica is believed to contribute about 10% to global sea level
rise.
But how the West
Antarctic and Greenland ice sheets respond to warmer temperatures is
the biggest unknown by far in trying to predict how fast the waters
will rise over the coming century and beyond.
A total melt of either
sheet would raise sea levels globally by several metres.
East Antarctica, by
contrast, is so cold that the ice is projected to remain solid for
centuries.
"Since the last
Intergovernmental Panel on Climate Change report [in 2007], which
highlighted uncertainties connected with ice sheets, almost every
significant piece of research we've produced has increased the
significance of the ocean for West Antarctica and Greenland,"
said Prof Vaughan.
"There are
changes in precipitation now and in future; but the really big,
potentially fast, changes are connected to the oceans, and the goal
for us is to model that system."
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