HALIFAX - At four times the size of Manhattan, it's easy to understand why a gargantuan island of ice drifting toward Canada's east coast is considered a looming threat to transatlantic shipping and offshore energy platforms.
But an ice expert says its sheer bulk, measured at 250 square kilometres, is not the real reason the lumbering hulk could play havoc with the shipping lanes off Newfoundland's Grand Banks.
Tony King, a senior project engineer with C-Core, a research firm that serves the offshore oil and gas sector, said the ice island — the largest of its kind in the northern hemisphere since 1962 — calved from a glacier that is notorious for producing icebergs with a deceptively low profile.
"They're easily lost in pack ice and they can sneak up on you," King said in an interview from his office in St. John's, N.L.
"Some fragments could well make it down into the shipping lanes and if you've got high seas, these things are very difficult to pick up on radar."
The flat-topped ice sheet has been dubbed Petermann Ice Island 2010, a reference to its origin: the Petermann Glacier in northwestern Greenland.
Trudy Wohlleben, senior ice forecaster with the Canadian Ice Service in Ottawa, was the first to confirm its birth as she scanned NASA satellite images last Thursday.
She also predicts the giant berg will break up.
"Smaller pieces are more of a threat to ships," she said. "But for the (oil and gas) platforms, they're not much of a threat because you can tow them out of the way. The big pieces are more of a threat to fixed platforms."
The frozen island has a long way to go before it poses a threat to anything, with some scientists saying the voyage could take between one and four years.
Along the way, the colossal slab could run aground or get trapped in a bay in the Arctic Ocean.
But even if it manages to avoid that fate, it will surely be eroded by salt water, pounded by waves and scraped by other icebergs.
"I've been tracking a number of ice islands over the years, and most of these end up drifting into places like Lancaster Sound and Ungava Bay," King said.
"The most you get is smaller fragments getting swept down ... (But) you're looking at a big enough mass that you could have tens of thousands of pieces coming off of it."
In 2008, the same Greenland glacier produced another ice island — about 25 square kilometres — that eventually drifted south of Baffin Island and broke up with little fanfare.
But some big fragments have made it much farther south.
In the late 1800s, a slab of ice measuring at least eight kilometres long made it as far as St. John's harbour, King said.
Today, an iceberg that large would be easily tracked by beacons, satellites and the International Ice Patrol, a branch of the U.S. Coast Guard that uses fixed-wing aircraft to warn mariners of icebergs.
The patrol was set up after another Greenland iceberg sank the Titanic in 1912.
As for the offshore energy sector, the only rig that can't be moved if an unusually large iceberg reached the Grand Banks is the 600,000-tonne Hibernia platform, owned by a consortium of energy companies.
King said the platform's concrete base, which sits in 80 metres of water, has been "over-engineered" to withstand an indirect strike from a six-million tonne iceberg.
"I really don't think Hibernia has anything to worry about," he said. "It would probably end up cutting through it like a cheese wire."
Margot Bruce-O'Connell, a spokeswoman for ExxonMobil Canada, said the iceberg wasn't an immediate concern.
"Given that it may develop into something in future years, it's not something that we would comment on at this stage," she said.
The rig has never been hit by an iceberg, though scores of them have been towed to a new course or blasted with water cannon.