What were you doing on Aug. 13, 2005? If you were a Canadian ice shelf, you were melting and breaking free. Yikes.

A giant ice shelf the size of 11,000 football fields has snapped free from Canada’s Arctic, scientists said. The mass of ice broke clear 16 months ago from the coast of Ellesmere Island, about 497 miles south of the North Pole, but no one was present to see it in Canada’s remote north. Scientists using satellite images later noticed that it became a newly formed ice island in just an hour and left a trail of icy boulders floating in its wake.

Warwick Vincent of Laval University, who studies Arctic conditions, traveled to the newly formed ice island and could not believe what he saw.

“This is a dramatic and disturbing event. It shows that we are loosing [sic] remarkable features of the Canadian North that have been in place for many thousands of years. We are crossing climate thresholds, and these may signal the onset of accelerated change ahead,” Vincent said Thursday…

Laurie Weir, who monitors ice conditions for the Canadian Ice Service, was poring over satellite images in 2005 when she noticed that the shelf had split and separated.

Weir notified Luke Copland, head of the new global ice lab at the University of Ottawa, who initiated an effort to find out what happened.

Using U.S. and Canadian satellite images, as well as data from seismic monitors, Copland discovered that the ice shelf collapsed in the early afternoon of Aug. 13, 2005.

“What surprised us was how quickly it happened,” Copland said. “It’s pretty alarming. Even 10 years ago scientists assumed that when global warming changes occur that it would happen gradually so that perhaps we expected these ice shelves just to melt away quite slowly, but the big surprise is that for one they are going, but secondly that when they do go, they just go suddenly, it’s all at once, in a span of an hour.”