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A deep crack on on Antarctica's Larsen C ice shelf has nearly severed off one of the largest icebergs ever recorded:
One of the largest icebergs ever recorded — 2,500 square miles, about the size of Delaware — is about to break off Antarctica, according to the European Space Agency. The iceberg could speed up the break-off of other ice chunks, eventually eating away at a barrier that prevents ice from flowing to the sea.
The impending iceberg is being carved from one of the continent's major ice shelves, called Larsen C. Scientists have been monitoring Larsen C for months now, as a deep crack has slowly extended over the course of 120 miles. Only about three miles of ice are keeping the iceberg attached to the shelf, ESA says. No one knows when it will break off — it could be any moment — but when it does, the iceberg will likely be 620 feet thick (about the height of the Waldorf Astoria hotel in New York) and contain roughly 1 trillion tons of ice. It'll be drifting north toward South America, and could even reach the Falkland Islands. "If so it could pose a hazard for ships in Drake Passage," Anna Hogg from the University of Leeds, said in a statement.
Also at BBC.
(Score: 3, Informative) by MrGuy on Thursday July 06 2017, @04:49PM (1 child)
It will shrink exactly to occupy the volume it currently displaces.
A floating object displaces exactly enough water to exactly balance the object's weight. i.e. an object floats at a height where the volume of the submerged portion would, if completely filled with water, have the same weight as the whole floating object.
The "trick" here is that the weight of the water IN THE ICEBERG doesn't change when it melts. If you measured the weight of the iceberg before it melted, and measured the resulting water after it melted, they'd weigh the same. Which means that the pre-melted iceberg and the post-melted iceberg displace the exact same amount of water. So the melting of the iceberg won't affect the sea level any.
Now, if the iceberg shelf was NOT currently floating (e.g. it was a kind of ice bridge over the ocean that was sitting ABOVE where it would "naturally float"), then you'd be correct that the calving off of the iceberg WOULD raise sea levels when the iceberg entered the water for the first time. My understanding is that's not how the antarctic ice shelves work (which makes sense - a 125-mile long chunk of ice being held higher than gravity would tell it to my a 3-mile frozen section would be fighting TREMENDOUS leverage at the narrow attachment point, and would certainly have broken off by now).
(Note for nitpickers - Yes, I'm ignoring some factors that technically come into play here, for example of the salinity of the iceberg and the salinity of the water it floats in aren't equal, the difference in density WOULD have an impact. Also, as the water warms post-melting, it actually shrinks slightly (up to 4 degrees C), then starts expanding. Those are things that can be factored in once we're clear on the general principals.)
(Score: 2) by c0lo on Thursday July 06 2017, @06:10PM
(imagination running amok,'ey?)
How about a piece of ice sustained by the sea bottom all the size? Like sea frozen there, then snow piling on top until the weight is too much to allow the ice to float?
In the extreme case, make the initial sea depth being zero and have only snow piling on top and compacting as ice?
Sounds familiar? Those are glaciers. When they melt, the sea level rises. Like the Greenland icesheet meltdown [sciencemag.org]
(yes, one can imagine glaciers that are actually advancing in the sea without calving icebergs - too thick to start with when pushed by the ice sheet behind. Or just surface melting until lightweight to stat floating. In both cases, the sea level will grow because of the water displaced or the result of melting)
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford