Several kilometres of ice have broken off the Erebus glacier ice tongue, which sticks out into McMurdo Sound in Antarctica.

The long thin tongue is thought to have calved three times in the 20th century, with the first of those occasions witnessed by Members of Robert F Scott's Terra Nova expedition during a gale in 1911.

It was thought to have calved again in the 1940s, and was recorded calving again in 1990, meaning the latest break has come some years earlier than had been expected.

Antarctic scientist Dr Tim Haskell said he had noticed the latest calving a few days ago by chance while looking at some satellite imagery.

There was no particular reason for it to have happened this summer.

"The sea ice conditions have probably worked out to make it easier for it to calve," Haskell said.

"There's open water all around it now and there's the odd [ice]berg floating around so it could have got hit by something."

It was difficult to work out the size of the tongue but it had probably been around 16km long before the calving, and probably around 3km had broken off.

Each kilometre that came off probably contained about five million tonnes of ice. If 5km had come off that would keep Auckland in water for about 150 years.

"That gives you some perspective of the size," Haskell said.

"It's interesting because it's a historical area. I guess it's interesting to see something happen now that happened when Scott was there."

The iceberg that had broken off would probably drift across to the other side of McMurdo Sound and go aground there, based on what had happened previously.

Work had been done on the tongue in the 1980s.

"We had a little bit of bad luck because at the end of '89 we took some of the equipment out to refurbish it. It had been there for six years and we took the risk that it (the tongue) wouldn't break that year but it did. So we got a lot of data on it's normal state but we didn't get the thing we really wanted," Haskell said.

"There's all sorts of stuff calving off Antarctica all the time. This ice tongue is a little bit different because it's very long and thin. That's probably because it's in a relatively sheltered area, it's in a sort of a bay and there are islands around. Once it grows out beyond the islands then it's exposed to the waves a lot more, and that might trigger it's calving."

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