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I've just seen the LiveScience article 70-Mile-Long Crack Opens Up in Anatarctica. I'm not sure if the title is a bit sensational or not, the crack is in an ice shelf, not the continent of Antarctica.

An ominous crack in an Antarctic ice shelf as wide as a football field is long takes on an otherworldly beauty in a new aerial image.

Snapped by scientists on NASA's IceBridge mission, the shot shows a rift in Larsen C, an ice shelf that is floating off the Antarctic Peninsula. When the crack eventually spreads across the entire ice shelf, it will create an iceberg the size of the state of Delaware, according to IceBridge. That's around 2,491 square miles (6,451 square kilometers).

As of Nov. 10, when the IceBridge scientists observed this crack, it was 70 miles (112 km) long and more than 300 feet (91 meters) wide. The dark depths of the crack plunge down about a third of a mile (0.5 km), all the way through the ice to the ocean below.

[...] Larsen C is Antarctica's fourth-largest ice shelf, and it holds back the land-based glaciers just behind it: Once the ice shelf goes, those slow-flowing glaciers have one less barrier in their journey toward the sea.

My primary question: is this a remarkable event, or something that over time happens regularly? Isn't this just a natural part of "those slow-flowing glaciers... journey toward the sea." ?

I'm also wondering 1) Is an iceberg the size of Delaware actually remarkable, or something that just happens from time-to-time? And 2) how they (actually) know the crack goes all the way to the ocean - can they actually see the water in images, or is this a hypothesis based on understanding of cracks of this length and width? I can ask as a separate questions if it's too much to ask here.

enter image description here

above: Image from here. "A huge crack can be seen in the Antarctic Peninsula's Larsen C ice shelf in this aerial image snapped on Nov. 10, 2016, as part of NASA's IceBridge mission. Credit: NASA/John Sonntag"



update:

The rift continues to be tracked. If I understand correctly, it is now over 350 meters wide and growing:

enter image description here

above: From A growing rift on Larsen C at the Project MIDAS website.

More can be read about NASA's operation Ice Bridge program at its official website. These are a series of areal flights over antarctic regionss to collect images and data. The image above of the crack in the Larsen-C ice shelf was a featured photo and more can be read about it here. In the image gallery the caption states:

Rift in Antarctica's Larsen C Ice Shelf

On Nov. 10, 2016, scientists on NASA's IceBridge mission photographed an oblique view of a massive rift in the Antarctic Peninsula's Larsen C ice shelf. Icebridge, an airborne survey of polar ice, completed an eighth consecutive Antarctic deployment on Nov. 18.

The photo was also featured in @NASA_ICE.

A short video explaining the mission and showing details of the aircraft's science equipment can be seen below (and is linked here):

https://www.youtube.com/watch?v=v3yMHHzLTCc

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    $\begingroup$ Nice picture. Any idea what's the scale on that? $\endgroup$ – Gimelist Dec 8 '16 at 2:26
  • $\begingroup$ @Michael Thank you for your question! I've added additional information and links about Operation Ice Bridge, and found more information about the rift at the MIDAS website. If I understand correctly, the rift is currently over 350 meters wide. According to the quote it was about 90 meters wide in the photo. $\endgroup$ – uhoh Dec 9 '16 at 3:20
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    $\begingroup$ some info here. but they are ship-base observations, so they'll probably biased towards small sized icegergs $\endgroup$ – shamalaia Dec 9 '16 at 10:21
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    $\begingroup$ @uhoh still hanging on bbc.com/news/science-environment-39055524 $\endgroup$ – DavePhD Feb 22 '17 at 17:18
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    $\begingroup$ @uhoh the iceberg finally calved in the last couple days $\endgroup$ – DavePhD Jul 12 '17 at 12:45
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Is an iceberg the size of Delaware [6,451 square kilometers] actually remarkable, or something that just happens from time-to-time?

In March 2000 iceberg B-15 formed which was 11,000 sq. km. and 295 km long.

In October 1998 iceberg A-38 formed which was 6,900 sq. km.

A Delaware size iceberg would be the 3rd largest in the past 20 years.

The 1990 article The calving and drift of iceberg B-9 in the Ross Sea, Antarctica Antarctic Science Vol. 2 , pages 243-257 says:

The largest iceberg in recent times (95 km x 95 km) calved from the Larsen Ice Shelf in early 1986

So a 9000 sq. km. iceberg broke off in 1986.

Contribution of giant icebergs to the Southern Ocean freshwater flux says:

an iceberg of 10,000 km2 in area broke from the Amery ice shelf in 1964

According to Antarctica shed a 208-mile-long berg in 1956:

A record iceberg seen in Antarctic

Little America V, Antarctica, Nov. 17- The U.S.S. Glacier, the Navy's most powerful icebreaker, has sighted an iceberg more than twice the size of Connecticut.

The berg was sighted by the Glacier early this week about 150 miles west of Scott Island. The ship reported it was 60 miles wide and 208 miles long- or more than 12,000 square miles, as against Connecticut's 5,009.

So 12,000 sq. mi. or 31,000 sq. km. is the largest known iceberg.

Both of the two previous references also mention a 1927 Antarctic iceberg that was 170 km long, but area is not given. American Practical Navigator, says the 1927 iceberg was 100 mile long and 100 miles wide, so 25,000 sq. km.

In summary, an iceberg the size of that contemplated in the OP can be expected on the once every 5-20 years time scale.

update 7/12/2017:

according to the MIDAS project:

The calving occurred sometime between Monday 10th July and Wednesday 12th July 2017, when a 5,800 square km section of Larsen C finally broke away. The iceberg, which is likely to be named A68

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    $\begingroup$ OK, that certainly puts it into perspective - thanks! $\endgroup$ – uhoh Jan 18 '17 at 15:06
  • $\begingroup$ I am not sure that you can say the last statement. It seems to me you have only listed a few occurrences in the last century. Do you have a reference that shows that? $\endgroup$ – Isopycnal Oscillation Jan 20 '17 at 7:30
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    $\begingroup$ @IsopycnalOscillation I'm just saying that based upon the 3 icebergs (2000, 1998, 1986) larger than Delaware in the satellite observation era. There were also icebergs in 1987 and 2002 that were just slightly smaller than Delaware (en.wikipedia.org/wiki/Iceberg_B-9 and en.wikipedia.org/wiki/Iceberg_C-19) $\endgroup$ – DavePhD Jan 20 '17 at 12:13
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    $\begingroup$ @IsopycnalOscillation and this article says the new iceberg would be 5000 sq km, in which case it would be the 6th largest since 1986: bbc.com/news/science-environment-38686626 and I might be missing some examples because "An iceberg the size of Jamaica" 2001 says: "On the other side of the continent, two immense icebergs calved from the Ronne Ice Shelf: A43 (250 km by 34 km)" antarctica.gov.au/magazine/2001-2005/issue-1-autumn-2001/… so I should add A43. I added a 1964 iceberg to my answer also. $\endgroup$ – DavePhD Jan 20 '17 at 16:04
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    $\begingroup$ @IsopycnalOscillation and the book "Ice in the Oceans" says that in 1986, in addition to the 95X95 km2 iceberg that broke off the Larsen ice shelf in Jan-Mar, a 90X210 km2 area of the Filchner self broke off in June. books.google.com/… $\endgroup$ – DavePhD Jan 20 '17 at 16:28
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Developing since 2014, the crack was projected in 2015 to lead to "the largest calving event since the 1980s," according to this report in The Cryosphere journal by glaciologists studying the region.

From 2010, "Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years" says that the largest break-up event in that period was the crack-up of Larsen B in 2002, which totalled 3,250 square kilometers -- approximately half the size of the area projected to break off from Larson C as a result of the current crack.

"Growing Crack in Antarctica's Larsen C Ice Shelf Spotted by NASA's MISR" explains that the Multiangle Imaging SpectroRadiometer (MISR) instrument aboard NASA's Terra satellite examine's Earth's surface with nine cameras pointed at different angles, which provides information about the texture of the surface. In composite images, the crack is clearly distinct from the surrounding ice shelf -- it is explained that the texture of the ice shelf is smooth and the texture of the sea ice on the ocean surface within the crack is rough.These images from NASA's Terra satellite show a large crack in the Larsen C shelf.

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    $\begingroup$ Excellent, thank you! I'll give those a read today. Would you be able to address "...:*is this a remarkable event, or something that over time happens regularly*?" For example over the last few thousand years, are these shelves breaking off in large chunks and being replenished regularly? $\endgroup$ – uhoh Jan 18 '17 at 1:11
  • $\begingroup$ @uhoh Hmm, that's a more challenging, since ice shelves by their nature fragment as the glaciers behind them push them out to sea, and then the resulting icebergs melt. (Unrelated: There are studies about the ecosystems floating bergs create and carry with them.) But I do know of research that has tried to tackle the long-term presence or absence of ice cover; ice affects what gets deposited in the sediments below, ranging from pollen to rocks conveyed by glacial action. I think those are mostly Arctic; I'll poke around. $\endgroup$ – jeffronicus Jan 18 '17 at 15:47
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    $\begingroup$ @uhoh Skimming the literature, it doesn't look like there is any analysis of historic calving events, that is, big individual chunks of the ice shelf breaking off. Most of the research on the topic addresses the broader extent of ice shelves through proxies such as sediment -- for example, a 100km retreat of the Ross Ice Shelf (about 10x bigger than Larsen C) over a 1000-year period ending about 1,500 years ago: pnas.org/content/113/9/2354.abstract $\endgroup$ – jeffronicus Jan 20 '17 at 17:45
  • $\begingroup$ thanks - I will take a look this weekend. When you say historic calving events, does a reliable history of events even exist that could be studied? $\endgroup$ – uhoh Jan 20 '17 at 18:52
  • $\begingroup$ @jeffronicus The US National Ice Center has tracked all icebergs larger than 10 nautical miles in at least one dimension since 1978, so there should be complete data since then. natice.noaa.gov/doc/Notice_Iceberg_Tracking_Criteria.pdf It's just a matter of getting access to the data. This is the current list of icebergs being tracked. natice.noaa.gov/pub/icebergs/Iceberg_Tabular.pdf $\endgroup$ – DavePhD Jan 21 '17 at 14:00

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