One of the biggest icebergs in history has snapped off the West Antarctic ice shelf, according to scientists who have been monitoring a growing crack for months.

Satellite images confirmed that the trillion-tonne iceberg had broken away and was adrift at sea.

"The calving occurred some time between Monday, July 10 and Wednesday, July 12, when a 5,800-square kilometre section of the ice shelf finally broke away," Swansea University said in a statement on Wednesday.

The massive sheet of ice with an area nearly as large as the size of the US state of Delaware had been developing a crack across the Larsen C ice shelf over the past few years.

The Larsen-C rift opening over the last 2 years from #Sentinel1 pic.twitter.com/MT9d3HAw1M — Adrian Luckman (@adrian_luckman) January 31, 2017

Ice shelves are floating masses of ice, hundreds of metres thick, that are fed by slow-flowing glaciers from the land.

Several ice shelves have cracked around northern parts of Antarctica in recent years.

By itself, the massive iceberg will not add to sea levels when it melts, but scientists worry about the effects it will have on inland glaciers.

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The ice shelves act as giant brakes, preventing glaciers from flowing directly into the ocean.

If the glaciers held in check by Larsen C spilt into the Antarctic Ocean, it would lift the global water mark by about 10 centimetres, researchers have said.



The calving of ice shelves occurs naturally, though global warming is believed to have accelerated the process.

Warming ocean water erodes the underbelly of the ice shelves while rising air temperatures weaken them from above.

Man-made global warming has already lifted average global air temperatures by about one degree Celsius since pre-industrial levels.

Antarctica is one of the world's fastest-warming regions.