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The giant ice wall is moving slowly from Antarctica and could collide with South Georgia, an important breeding ground for wildlife.
Satellite images show that unlike previous "megabergs", this ice is not breaking up into smaller pieces as it moves through the Southern Ocean, said Andrew Majors, a physical oceanographer at the British Antarctic Survey.
He said its exact course is difficult to predict, but prevailing currents suggest the colossus will reach the shallow continental shelf around South Georgia in two to four weeks.
But what will happen after that can only be guessed, he said.
The giant iceberg could avoid the shelf and drift into open waters beyond South Georgia, a British overseas territory about 1,400 km east of the Falkland Islands.
Or it could hit the sloping seabed, run aground for months or break into pieces.
Majors said that scenario could seriously disrupt the seals and penguins that try to feed and raise their young on the island.
"In the past, icebergs have gotten stuck out there and it's caused significant mortality to baby penguins and seals," he said.
The world's largest and oldest iceberg, known as A23a, is about 3,500 square kilometres in diameter and separated from the Antarctic shelf in 1986.
It remained stuck for more than 30 years until finally breaking free in 2020, its northward journey sometimes slowed by ocean forces that held it in place.
Myers, who came face-to-face with the iceberg while leading a science mission in late 2023, described "a huge white rock 40 or 50 meters high that stretched from horizon to horizon."
"It's just like a white wall. It's actually very similar to the one in Game of Thrones," he said, describing that he had "the feeling that the wall would never end."
A23a has followed roughly the same path as previous giant icebergs, passing along the eastern side of the Antarctic Peninsula through the Weddell Sea along a route called "iceberg lane".
Weighing just under 1 trillion tonnes, this monstrous block of fresh water was carried by the world's most powerful ocean 'jet stream' - the Antarctic Circumpolar Current.
Myers said it moved "more or less in a straight line from where it is now to South Georgia," where the waters quickly became shallow and the current bent sharply.
He said the iceberg could follow the current out to sea or become stuck on the shelf.
It's summertime in South Georgia, and the penguins and seals that live along the southern coast undertake foraging expeditions into the frigid waters to bring in enough food to feed their young.
"If an iceberg parks there, it will either physically block where they feed or they will have to go around it. That burns a tremendous amount of extra energy for them, so that's less energy for the hatchlings and chicks, which leads to increased mortality," Majors says.
South Georgia's seal and penguin populations are already having a "bad season" with the bird flu epidemic, "and this (iceberg) is going to make it significantly worse. That would be pretty tragic, but not unprecedented," he added.
When A23a melts, it could flood the ocean with small but still dangerous chunks of ice that fishermen would have a hard time navigating, Majors added.
It would also load the water with nutrients that promote phytoplankton growth, giving food to whales and other species and allowing scientists to study how such blooms absorb carbon dioxide from the atmosphere.
Although icebergs are a very natural phenomenon, Majors said the rate at which they are being lost from Antarctica is increasing, possibly due to human-induced climate change. | BGNES
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