
Scientists monitoring a rift in an Antarctic ice shelf where an iceberg the size of south Wales is poised to break off say the huge crack in the ice has spread.

Late last year a rift in the Larsen C Ice Shelf grew suddenly by around 18 kilometres (11 miles), leaving a vast iceberg more than 5,000 square kilometres (1,900 square miles) 'hanging by a thread'.

Just 20 kilometres (12 miles) of ice connects the iceberg to the rest of the ice shelf. The main rift continued to grow early this year and is currently 180 kilometres (110 miles) long.

Now satellite data has revealed a second branch of the rift, some 15 kilometres long (nine miles), is moving towards the edge of the ice, according to researchers at Swansea University.

Scientists monitoring a rift in an Antarctic ice shelf where an iceberg a quarter the size of Wales is poised to break off say the huge crack in the ice has spread. The rift is likely to lead to an iceberg breaking off, which will remove about 10 per cent of the ice shelf's area. Pictured is a graphic on how the rift has progressed over the years, including the formation of a new branch

WHAT HAPPENED TO LARSEN B? In 2002 a massive section of the Larsen B ice shelf disintegrated in just 32 days. The 656 feet (200m) thick ice sheet broke apart into thousands of ice bergs that gradually drifted away over several years In total 1,235 square miles of ice collapsed into the sea. It is thought increased ice flow from behind the ice shelf had weakened it and caused cracks to appear. Melt water flowing into these cracks acted as wedges that forced the ice shelf apart, causing it to shatter. About 1,620 square kilometres (625 square miles) of Larsen B remains - an area roughly the size of Lake Superior and Lake Michigan combined. Advertisement

When the ice breaks off it is likely to lead to one of the biggest icebergs ever recorded.

Professor Adrian Luckman, of Swansea University College of Science, said: 'While the previous rift tip has not advanced, a new branch of the rift has been initiated.

'This is approximately 10 kilometres (six miles) behind the previous tip, heading towards the ice-front.'

He said it was the first significant change to the rift since February, but added: 'Although the rift length has been static for several months, it has been steadily widening, at rates in excess of a metre per day.'

And he said: 'When it calves, the Larsen C Ice Shelf will lose more than 10 per cent 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.'

The researchers warned the ice shelf will be less stable after the iceberg calves, and could follow the example of its neighbouring ice shelf Larsen B, which disintegrated in 2002 after a similar event.

A team of researchers flew over the gigantic crack in the ice in December and calculated it to be about 112 kilometres (70 miles) long, more than 90 metres (300 feet) wide and about half a kilometre (0.3 miles) deep.

It has since grown to around 180 kilometres (110 miles) long.

'The crack completely cuts through the Ice Shelf but it does not go all the way across it – once it does, it will produce an iceberg roughly the size of the state of Delaware,' NASA said in a press release in December.

Satellite data has revealed a second branch of the rift, some 15km long (nine miles), is moving towards the edge of the ice, according to researchers at Swansea University. This graph shows the velocity of the ice surface in metres per day. White and pink indicate areas where the ice is separating at rapid speeds of more than two metres per day

Lead researcher Professor Luckman said the iceberg was 'hanging by a thread'.

When it calves off, the Larsen C Ice Shelf will lose more than 10 per cent of its area, fundamentally changing the landscape of the Antarctic Peninsula, and making the shelf less stable, the experts said.

The current event is not an ice shelf collapsing, but Larsen C may, in years or decades to come, follow the course of the Larsen B Ice Shelf which splintered and collapsed in the space of a month in 2002, they said.

Speaking to the BBC, Professor Luckman, said: 'If it doesn't go in the next few months, I'll be amazed.

Two radar images from April 7 and 14, 2017 were combined to create this so-called interferogram showing the growing crack in Antarctica’s Larsen-C ice shelf. The crack is seen to the right hand side of the image in red. The colored fringes show displacement on the surface of the ice shelf

Late last year a rift in the Larsen C Ice Shelf (pictured) grew suddenly by around 18 kilometres (11 miles), leaving a vast iceberg more than 5,000 square kilometres (1,900 square miles) 'hanging by a thread'

'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.'

Professor Luckman says that when the iceberg breaks off, it will be among the 10 biggest ever recorded.

The collapse of the Larsen B ice shelf on the east side of the Antarctic Peninsula in 2002 saw a 1,235 square miles (3,200 square km) section of ice break apart into thousands of icebergs in just 35 days.

The Larsen C Ice Shelf is primed to lose an area of more than 1,900 square miles (5,000 square kilometres), after a rift in the ice shelf grew suddenly by around 11 miles (18 km) in the second half of December. Pictured is the view of a recently discovered 300-ft wide rift in the Larsen C

Map of Antarctica showing the amount of melting of ice shelves from below. Blue shades represent melt rates of greater than 5 meters per year. Arrow points to Larsen C Ice Shelf

Larsen B was thought to have been stable for up to 12,000 years, according to studies on the collapse, but had become a hotspot of global warming.

Previous studies had suggested that the ice shelf began melting only a few years before it disintegrated in 2002.

Rising summertime temperatures are thought to have increased the water flow into cracks which then acted like wedges to lever the ice shelf apart.

It sparked widespread concern about the impact that climate change is having on the ice sheet balance in Antarctica, although a recent study showed ice mass on the continent has actually increased.

The current event is not an ice shelf collapsing, but Larsen C may, in years or decades to come, follow the course of the Larsen B Ice Shelf which splintered and collapsed in the space of a month in 2002, they said. Pictured is the Larsen B Ice Shelf before its breakup in 2002

Over the course of a couple of months, a huge section of the Larsen B Ice Shelf completely disappeared after breaking up

The Larsen B ice shelf is thought to be one of the largest collapses of sea ice to have been witnessed. It lies off the east coast of the Antarctic Peninsula, which is thought to be a warming hotspot

IS ANTARCTICA GAINING ICE? Antarctica is gaining more ice than it loses, research by Nasa last year found. It said Antarctica's ice sheet is thickening enough to outweigh losses caused by melting glaciers. The research challenges the conclusions of the Intergovernmental Panel on Climate Change's report, which says that Antarctica is losing land ice. But it also warns that losses could offset the gains in years to come. The increase in Antarctic snow began 10,000 years ago and continues in East Antarctica and the interior of West Antarctica by an average of 0.7 inches (1.7cm) per year, according to the space agency. Advertisement

The researchers say the acceleration of ice flow seen in the Larsen B ice shelf may be due to changes in the properties of the ice itself.

Melting may have caused the ice to become more plastic and increased the slipperiness of the ice behind the ice shelf, pushing it further out to sea.

The collapse of the Larsen Ice shelf in 2002, which is one of the biggest on record, is thought to have triggered further acceleration and thinning of the glaciers behind it.

There are now growing fears over the remaining section of the Larsen B ice shelf - which covers around 1,620 square kilometres (625 square miles), and the large Larsen C ice shelf further to the south.

A recent study revealed that on the opposite side of the Antarctic Peninsula, more than 1,000 square kilometres (386 square miles) of ice – an area the size of Berlin – has been lost in the past 40 years.

But elsewhere in the Antarctic, the ice sheet has been growing. Satellite data showed that the continent's vast ice sheet has showed a net gain of 112 billion tons of ice each year between 1992 and 2001.

However, between 2003 and 2008, that has slowed to 82 billion tons of ice per year.