Scientists Check 5 Sq Mile Calving From Jakobshavn Glacier; If Confirmed, Likely Largest On Record
While examining satellite images of Greenland’s massive Jakobshavn glacier over the weekend, members of the Arctic Sea Ice Forum noticed something odd: Between August 14 and August 16, it appeared as though a huge chunk of ice — which some guessed might be the largest ever observed — broke away from the glacier’s face. Members of the forum estimate that the total area of ice lost from the edge of the glacier (that is, the area lost when looking at the top surface of the glacier from above, using the satellite images) was around 12.5 square kilometers, or nearly five square miles, according to a post on the Arctic Sea Ice Blog, which is operated by ice enthusiast Neven Curlin. If correct, this would be one of the largest such chunks of ice ever to split from the glacier.
“Calving,” which is when ice breaks away from the edge of a glacier or ice sheet and tumbles into the water, is not unusual for this area in Greenland. A combination of rising air and sea temperatures in the Arctic have made calving events more severe in recent decades, and in fact, the Jakobshavn glacier is one of the fastest flowing glaciers in the world, meaning it bleeds ice into the ocean at one of the highest rates of any ice sheet on Earth. As of 2012, the glacier was pouring out ice at a speed of 150 feet per day, nearly three times its flow rate in the 1990s.
But last weekend’s event was big enough to turn heads, and the Arctic Sea Ice Blog post suggested that this incident might be the biggest calving event on record. However, some scientists aren’t so sure — and their doubt highlights some key uncertainties in human interpretations of ice calving events.
“Overall, I don’t think that they really can nail the ‘largest’ [calving event] or not,” wrote Richard Alley, a glaciologist at Pennsylvania State University, in an email to the Post. According to Alley, the time resolution on the satellite images, which are spaced by a full day, is poor enough that the ice loss could have occurred in several smaller events rather than one large one. Alley adds, “I wouldn’t get too excited on this, even though it is not good news.” However, Jason Box, a glaciologist with the Geological Survey of Denmark and Greenland, says he wouldn’t rule out the possibility that this calving event is the largest to occur. And Eric Rignot, a principal scientist and ice expert at NASA’s Jet Propulsion Laboratory, says that whether or not the event is the largest on record, he’s “struck by the sheer size of this calving event,” which he says is evidence that the glacier is continuing to retreat at “galloping speed.”
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http://www.washingtonpost.com/news/energy-environment/wp/2015/08/19/one-of-the-worlds-fastest-melting-glaciers-may-have-just-lost-its-biggest-chunk-of-ice-ever/