An enormous iceberg half the size of Greater London that broke off an Antarctic glacier last year is headed for the open ocean, scientists said on Wednesday.

B31, which calved from Pine Island glacier last November, is large enough at 33km long and 20km wide to lead Nasa to monitor its movements via satellite. It is up to 500 metres thick.

Nasa glaciologist Kelly Brunt said: "It's one that's large enough that it warrants monitoring," noting that US agencies monitored several dozen icebergs at any one time.

B31 (top left) seen on 11 March, 2013. The iceberg, 33km long and 20km wide, is headed for the open ocean. Credits: MODIS/Terra/NASA Photograph: NASA

Brunt said the iceberg was not in a particularly busy shipping area at the moment. However, Dr Bethan Davies, a research scientist at the University of Reading, said it could head into areas with more ships.

"It's floating off into the sea and will get caught up in the current and flow around the Antarctica continent where there are ships," she told Sky News.

She said by itself the iceberg would not significantly contribute to sea level rises but that Pine Island Glacier itself had the potential to raise sea levels by 1.5m, although there is uncertainty over long it will take to melt. "[The iceberg itself] could take a very long time to melt, well over a year or even longer," said Davies.



Scientists are also able to track B31 via sensor-laden "javelins" that were dropped onto it in 2013 and have GPS trackers.