“The iceberg may have run aground just before colliding. 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.

“What may be needed to release it from its present stalled location is for the surface currents to turn it into the wind, combined with help from a mixture of wind, tides and bottom melting to float it off its perch.”

The plodding course of the Long Island-sized iceberg, which scientists predicted would crash into an Antarctic glacier by 15 January, has been halted indefinitely.

The iceberg, called B-15A, has run aground about four kilometres from the Drygalski Ice Tongue and is "just jiggling back and forth", says Julie Palais, a glaciologist who works at McMurdo Station, a US Antarctic research base. It will probably stay like this for some time, she adds.

The threat of sea access being blocked to US and New Zealand bases in Antarctica may have receded after the world's largest iceberg broke free from the McMurdo Sound sea bed last month, New Zealand Antarctic officials said.

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The previous position of the iceberg had caused a build up of sea ice in McMurdo Sound, threatening access by US ice-breaking ships to New Zealand's Scott Base and the nearby US McMurdo Sound base.

The giant B-15A iceberg has menaced the Drygalski Ice Tongue since December 2004. At 122 kilometers (76 miles) in length by 28 kilometers (17 miles) in width, the bullying iceberg charged with great momentum towards the ice tongue, threatening to shatter the floating extension of the Davis Glacier.

A scant five kilometers from Drygalski, B-15A ground to a stop, most likely grounded in the shallower waters near the shore. In the weeks that followed, the iceberg rotated free, until finally it began to drift past the ice tongue into the Ross Sea. Just when it looked as if Drygalski might escape a collision, B-15A delivered a glancing blow, knocking the end of the ice tongue loose.

Measuring around 115 kilometres in length with an area exceeding 2500 square kilometres, the B-15A iceberg is the world's largest free-floating object. It is the largest remaining section of the even larger B-15 iceberg that calved from the Ross Ice Shelf in March 2000 before breaking up into smaller sections.

Since then its B-15A section has drifted into McMurdo Sound, where its presence blocked ocean currents and led to a build-up of sea ice that decimated local penguin colonies, deprived of open waters for feeding. During the spring of this year prevailing currents took B-15A slowly past the Drygalski ice tongue. A full-fledged collision failed to take place, but a glancing blow broke the end off Drygalski in mid-April.

The stretch of Victoria Land coast parallel to B-15A's current position is unusually rich in wildlife, noted for colonies of Adelie penguins as well as Weddell seals and Skuas. If B-15A were to remain in its current position for any prolonged length of time, the danger is that the iceberg could pin sea-ice behind it, blocking the easy access to open water that local animal inhabitants currently enjoy.