In 2010, the remote Petermann Glacier in northwestern Greenland caught the public’s attention when a chunk of ice four times the size of Manhattan broke off into the ocean. Now, it has lost another big piece: on Monday, a chunk of ice about two times the size of Manhattan broke free and set sail.

NASA, via the University of Delaware

If a piece only twice as big as Manhattan doesn’t impress you, keep in mind that this ice island may be significantly thicker than the chunk set loose two years ago, so in total ice volume lost to sea, the event may be comparable, researchers say.

The fracture along which the latest piece of ice broke was first observed about eight years ago, so the event is not a big surprise. What is striking, scientists say, is that the two events happened in such quick succession; ice calving of this magnitude is usually seen only every 10 or 20 years.

“I think the glacier will be quiet now for a while,” said Andreas Münchow, an associate professor of physical ocean science and engineering at the University of Delaware’s College of Earth, Ocean and Environment. Dr. Münchow helped report the calving on Monday along with Trudy Wohlleben of the Canadian Ice Service.



Dr. Münchow points out that while the ice islands make for striking photography, the vast majority of ice loss from the Petermann glacier — some 80 percent to 90 percent — occurs from melting deep underwater, near what is known as the hinge line, or the point where Greenland’s bedrock meets the waters of Petermann’s Fjord and the ice sheet of Greenland.

The big question is therefore not so much how large the latest piece to break off is, but how a warming Atlantic, among other factors, is going to affect the position of the invisible hinge line. Its retreat could lead to greatly accelerated ice loss.

But figuring out exactly what’s going on deep underwater in a remote part of Greenland over many years isn’t exactly a straightforward exercise.

“Measuring the water temperature sounds easy enough, but not when you have to use a submarine to do it, or drill through 100 meters of ice,” Dr. Münchow said. “Not to mention just the expense of getting out there. I just bought a one-way ticket for $3,000.”

Dr. Münchow will travel to the region to retrieve monitoring instruments installed in 2009 in the Nares Strait between Greenland and Canada. The measurements recorded include salinity, current, temperature and ice-thickness data, including readings for the period when the 2010 ice island passed through.