A giant iceberg double the size of Sydney Harbour is on a slow but steady collision course with Australia, scientists have said.

The mammoth chunk of ice, which measures 12 miles long and five miles wide, was spotted floating surprisingly close to the mainland by scientists at the Australian Antarctic Division (ADD).

Known as B17B, it is currently drifting 1,000 miles from Australia’s west coast and is moving gradually north with the ocean current and prevailing wind.

Dr Neal Young, a glaciologist working for the ADD, said that if the iceberg eventually reached Australia waters, it would crash into the continental shelf causing a magnitude three to to four tremor.

However, Dr Young said the iceberg was unlikely to hit the Australian mainland. If it continued on its path north, it would eventually break up into hundreds of smaller icebergs, he said.

“As the waters warm, the iceberg will thin out, so it is not going to get to Australia, the further north it goes, the more it break up,” he said.

The smaller icebergs created when the larger berg broke up could become shipping hazards if they float closer to shore.

Dr Young said an iceberg the size of B17B had not been seen so far north since the days when 19th century clipper ships plied the trade route between Britain and Australia.

“Icebergs do come from time to time and they can be very big, but it can be a long time before we spot one – so it’s really a once-in-a-lifetime sighting.”

Originally three times its current size, the iceberg broke off Antarctica’s Ross Ice Shelf in 2000 along with several others.

B17B has since travelled thousands of miles and a third of the way around Antarctica thanks to ocean currents and winds.

It stayed completely still in one spot for about five years, but is now on the move again.

Dr Young originally spotted the iceberg using satellite images from Nasa and the European Space Agency.

It has an area equating to 87 square miles – roughly double the size of Sydney Harbour.

Several large icebergs have been sighted off Australia and New Zealand in recent weeks, but none rival B17B in size.

Last month a giant iceberg the length of seven football pitches was spotted off Australia’s Macquarie Island, about 930 miles southeast of Tasmania.

Dr Young said sightings of large icebergs could become more frequent if sea temperatures rise through global warming.

Icebergs are formed as the ice shelf develops. Snow falls on the ice sheet and forms more ice, which flows to the edges, onto the floating ice shelves.

Eventually, pieces around the edge break off.

[via: telegraph.co.uk]

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