An iceberg the size of Norfolk is poised to break away from a vast ice shelf in the north-west area of Antarctica. 
 
 Only a threadlike sliver 12 miles wide is keeping the 1,900sq-mile chunk attached to the Larsen C ice shelf in the Weddell Sea. 
 
 Professor Adrian Luckman of Swansea University told the BBC: "If it doesn't go in the next few months, I'll be amazed." 
 
 When it eventually breaks away, a process known as calving, the iceberg is predicted to be one of the top ten largest ever on record. 
 
 A massive crack in the 1150ft-thick ice shelf first appeared decades ago, says the BBC, "but in December the speed of the rift went into overdrive, growing by a further 18km [11 miles] in just a couple of weeks". 
 
 A Nasa photograph of the fracture shows it measures around 70 miles long, is 300ft wide and runs a third of a mile deep. 
 
 Larsen C was the largest of three adjoining ice shelves, until Larsen A and B both broke up in 1995 and 2002 respectively. Larsen B "disintegrated" after developing a similar rift, Nasa says. 
 
 The collapse of the millennia-old shelves was partially attributed to the effects of climate change, as warmer waters lapped away at the edges of the ice. 
 
 Ice shelves act as a barrier between the glaciers which flow off of the Antarctic mainland and the open sea. If the last intact section of the Larsen ice shelf were to disintegrate, leaving the glaciers to float away from the polar continent, scientists estimate global sea levels would rise by 4ins. 
 
 However, any future collapse of Larsen C is likely to be well into the future, say researchers. 
 
 "We would expect in the ensuing months to years further calving events and maybe an eventual collapse," Professor Luckman said. "But it's a very hard thing to predict and our models say it will be less stable, not that it will immediately collapse or anything like that." 

 Image copyright Adrian Luckman Image caption A huge iceberg, a quarter the size of Wales, is poised to break off from the Larsen C ice shelf 
 
 An iceberg expected to be one of the 10 largest ever recorded is ready to break away from Antarctica, scientists say. 
 
 A long-running rift in the Larsen C ice shelf grew suddenly in December and now just 20km of ice is keeping the 5,000 sq km piece from floating away. 
 
 Larsen C is the most northern major ice shelf in Antarctica. 
 
 Researchers based in Swansea say the loss of a piece a quarter of the size of Wales will leave the whole shelf vulnerable to future break-up. 
 
 Larsen C is about 350m thick and floats on the seas at the edge of West Antarctica, holding back the flow of glaciers that feed into it. 
 
 Researchers have been tracking the rift in Larsen C for many years, watching it with some trepidation after the collapse of Larsen A ice shelf in 1995 and the sudden break-up of the Larsen B shelf in 2002. 
 
 Last year, researchers from the UK's Project Midas reported that the Larsen C rift was growing fast. 
 
 But in December the speed of the rift went into overdrive, growing by a further 18km in just a couple of weeks. What will become a massive iceberg now hangs on to the shelf by a thread just 20km long. 
 
 Image copyright NASA Image caption The rift is about 100m wide but is estimated to be half a kilometre deep 
 
 Image copyright NASA Image caption Images taken in November last year show the length of the rift 
 
 "If it doesn't go in the next few months, I'll be amazed," project leader Prof Adrian Luckman, from Swansea University, told BBC News. 
 
 "There hasn't been enough cloud-free Landsat images but we've managed to combine a pair of Esa Sentinel-1 radar images to notice this extension, and it's so close to calving that I think it's inevitable." 
 
 Prof Luckman says the area that will break off will be about 5,000 sq km, a size he says that would put the iceberg among the top 10 biggest that have been recorded. 
 
 The researchers say that this is a geographical and not a climate event. The rift has been present for decades, they say, but it has punched through at this particular time. 
 
 It is believed that climate warming has brought forward the likely separation of the iceberg but the scientists say they have no direct evidence to support this. 
 
 However, they are concerned about how any break-off will impact the rest of the ice shelf, given that its neighbour, Larsen B, disintegrated spectacularly in 2002 following a similar large calving event. 
 
 Image copyright SPL Image caption The collapse of the Larsen B ice shelf which occurred in 2002 followed on from a large rift calving event 
 
 "We are convinced, although others are not, that the remaining ice shelf will be less stable than the present one," said Prof Luckman. 
 
 "We would expect in the ensuing months to years further calving events, and maybe an eventual collapse - but it's a very hard thing to predict, and our models say it will be less stable; not that it will immediately collapse or anything like that." 
 
 As it floats on the sea, the resulting iceberg from the shelf will not raise sea levels. But if the shelf breaks up even more, it could result in glaciers that flow off the land behind it to speed up their passage towards the ocean. This non-floating ice would have an impact on sea levels. 
 
 According to estimates, if all the ice that the Larsen C shelf currently holds back entered the sea, global waters would rise by 10cm. 
 
 All that is very much in the future. There are few certainties right now apart from an imminent change to the outline of Antarctica's icy coast. 
 
 "The eventual consequences might be the ice shelf collapsing in years to decades," said Prof Luckman, 
 
 "Even the sea level contribution of this area is not on anybody's radar; it's just a big geographical event that will change the landscape there." 
 
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 The Larsen C Ice shelf in Antarctica is primed to shed an area of more than 5000 sq. km following further substantial rift growth. After a few months of steady, incremental advance since the last event, the rift grew suddenly by a further 18 km during the second half of December 2016. Only a final 20 km of ice now connects an iceberg one quarter the size of Wales to its parent ice shelf. 
 
 The current location of the rift on Larsen C, as of January 2017. Labels highlight significant jumps. Tip positions are derived from Landsat (USGS) and Sentinel-1 InSAR (ESA) data. Background image blends BEDMAP2 Elevation (BAS) with MODIS MOA2009 Image mosaic (NSIDC). Other data from SCAR ADD and OSM. 
 
 When it calves, the Larsen C Ice Shelf will lose more than 10% of its area to leave the ice front at its most retreated position ever recorded; this event will fundamentally change the landscape of the Antarctic Peninsula. We have previously shown that the new configuration will be less stable than it was prior to the rift, and that Larsen C may eventually follow the example of its neighbour Larsen B, which disintegrated in 2002 following a similar rift-induced calving event. 
 
 For more details, see the coverage of this event at the BBC. 
 
 The development of the rift length and width, up to January 2017 
 
 The MIDAS Project will continue to monitor the development of the rift and assess its ongoing impact on the ice shelf.
– A chunk of ice the size of Delaware is clinging to an Antarctic ice shelf by "a thread" that could snap at any moment and create one of the 10 largest icebergs ever recorded, researchers say. Following the collapse of the nearby Larsen A ice shelf in the Weddell Sea in 1995 and Larsen B shelf in 2002, scientists noticed a rift in Larsen C, which is more than 1,100 feet thick. The rift has been extending across the ice shelf ever since, but over two weeks in December, it stretched an additional 11 miles in length, per the BBC. As of mid-December, it measured 70 miles long, the length of a football field in width, and a third of a mile deep, and had left a 2,000-square-mile chunk of ice attached to the shelf only by a 12-mile "thread" of ice, reports the Week, via NASA. "It's so close to calving that I think it's inevitable," says researcher Adrian Luckman. "If it doesn't go in the next few months, I'll be amazed." The break will cause Larsen C to lose more than 10% of its area, leaving it "at its most retreated position ever recorded," researchers say on a project website. They believe it will also make Larsen C less stable. "We would expect in the ensuing months to years further calving events, and maybe an eventual collapse" in years or decades, Luckman says, though other scientists aren't convinced. If the entire ice shelf were to enter the sea, global sea levels could rise by 4 inches, according to estimates. For now, though, this is "just a big geographical event," Luckman says. (Scientists are searching Antarctica for 1.5-million-year-old ice.)