The imagery was acquired on 19th January by ESA’s Sentinel-1 satellites.  It shows a further 10 km of rift growth since January 1st, bringing its total length to 175 km.

Prof Adrian Luckman of Swansea University College of Science described the latest findings:

"We can report a further extension of the rift which threatens to calve an iceberg measuring more than 5,000 sq. km in area from the Larsen C Ice Shelf.

The rift has continued to grow parallel to the shelf edge, so the iceberg remains attached by around 20 km of ice.

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.

The MIDAS Project will continue to monitor the development of the rift and assess its ongoing impact on the ice shelf. Further updates will be available on this blog, and on our Twitter feed."

UPDATED MAP - showing the extra growth in the rift as at 19 January 2017

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.

Researchers based in Swansea University’s College of Science 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 approximately 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, following the collapse of the 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.

Project leader, Professor Adrian Luckman, said: "If it doesn't go in the next few months, I'll be amazed.

"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."

According to Professor Luckman, the area that will break off will be about 5,000 sq km, a size he said that would put the iceberg among the top ten biggest ever recorded.

Professor Luckman added that this is a geographical and not a climate event. Although it is believed that climate warming has brought forward the likely separation of the iceberg.

However, the researchers say they have no direct evidence to support this.

They are concerned, though, 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.

"We are convinced, although others are not, that the remaining ice shelf will be less stable than the present one," said Professor 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."

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.

"The eventual consequences might be the ice shelf collapsing in years to decades," said Professor 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."

New video footage of the Larsen C Ice Shelf

British Antarctic Survey (BAS) recently captured this footage of a huge crack in the Larsen C Ice Shelf, on the Antarctic Peninsula.

Currently a huge iceberg, roughly the size of Norfolk, looks set to break off Larsen C Ice Shelf, which is more than twice the size of Wales. Satellite observations from February 2017 show a growing crack in the ice shelf which suggests that an iceberg with an area of more than 5,000 km² is likely to calve soon.

Researchers from the UK-based MIDAS project, led by Swansea University, have reported several rapid elongations of the crack in recent years. BAS scientists are involved in a long-running research programme to monitor ice shelves to understand the causes and implications of the rapid changes observed in the region. They shot this footage as they flew over the ice shelf on their way to collect science equipment.

During the current Antarctic field season, a glaciology research team has been on Larsen C using seismic techniques to survey the seafloor beneath the ice shelf.  Because a break up looks likely the team did not set up camp on the ice as usual.  Instead they made one-off trips by twin otter aircraft supported from the UK’s Rothera Research Station.

Ice shelves in normal situations produce an iceberg every few decades. There is not enough information to know whether the expected calving event on Larsen C is an effect of climate change or not, although there is good scientific evidence that climate change has caused thinning of the ice shelf. Once the iceberg has calved, the big question is whether Larsen C will start to retreat.