A huge collision expected to occur between the world's biggest iceberg and an Antarctic promontory may not happen.
The B-15A iceberg (right) heads for the Drygalski Ice Tongue (top left)
The 160km-long (99-mile) B-15A iceberg was heading toward a floating glacier known as the Drygalski Ice Tongue.
But the European Space Agency (Esa) said B-15A's progress had slowed in recent days and it may have run aground in shallow waters off McMurdo Sound.
The 3,000 sq km monster was supposed to have smashed into the tongue by last Saturday at the latest, experts said.
"The iceberg may have run aground just before colliding," said Mark Drinkwater of Esa's Ice/Oceans Unit, which has been monitoring the situation via the agency's Envisat satellite.
"This supports the hypothesis that the seabed around the Drygalski Ice Tongue is shallow, and surrounded by deposits of glacial material that may have helped preserve it from past collisions, despite its apparent fragility."
However, he warned, even if B-15A had stalled, it might not be for long.
Surface currents could turn the iceberg - which is about the same size as Luxembourg - towards the wind. If this happened, the wind, tides and bottom melting could float it off its perch.
Some scientists had dubbed the predicted meeting between the two giant ice slabs "the collision of the century".
Robert Binshadler, a researcher at the US space agency's (Nasa) Goddard Flight Center in Maryland, US, had said that the Drygalski Ice Tongue could even break off if the iceberg ploughed into it.
But it was more likely that their edges would crumple and ice would pile off or drift into the Ross Sea.
B-15A has a history of trouble-making. It is the largest fragment of a much larger iceberg that broke off from the Ross Ice Shelf in 2000.
This year, it trapped sea ice in McMurdo Sound. The currents that normally break the ice into pieces and sweep it out into the Ross Sea have not been able to clean out the Sound.
So winter's thick ice remains intact - causing problems for Antarctic residents.
Penguins, for example, have to swim greater distances to reach open waters and food.
As a result, there is a danger many chicks could starve, according to Antarctica New Zealand, the government organisation that oversees the country's research.