An Iceberg swarm at the mouth of the Ilulissat Icefjord World Heritage Site. Six miles wide, it drains one seventh of the Greenland Ice Sheet. Its source is the Jakobshavn Glacier that set a new world speed record for any glacier on Earth at 160 feet per day in 2013. But glacier is hardly a term for it today. Throughout recorded history the Jakobshavn has always flowed from the ice sheet into the 25 mile long, over half mile deep fjord, at least until the last several years. Since 1850 the glacier has been retreating up the icefjord towards the ice sheet. About the turn of the 21st century the retreat rate radically increased until 2006 when it completed its retreat to the edge of the ice sheet and stalled. The stall lasted until about 2011 and we know now that it was stuck on a sill, or high point where the icefjord meets the ice sheet. We also know now that the icefjord trench gets a lot deeper just inland of the sill and the retreat, if it can be called such, has started again. Only now, ice flows into the icefjord channel from three sides instead of one via multiple flow streams, and the calving front has widened by 30 percent to eight miles across.
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The average discharge of the Icefjord is 300 million tons per day and has quadrupled (average) in the last 20 years. It calves bergs that are a mile or more across and up to 3,000 feet deep. The icefjord is over 3,000 feet deep. Icebergs jam at its mouth where it meets Disko Bay, a small bay off of Baffin Bay. There is another sill at the mouth of the icefjord, just a mile outside of Ilulissat. The icebergs jam there unto pressure builds up from behind and then a massive swarm of bergs bursts through in a tumultuous cataclysm of smashing icebergs.
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The over-deepened fjord beyond the sill on the interior of the ice sheet is 4,600 feet deep and extends to the center of Greenland where the 11,000 foot-tall ice sheet has depressed land to up to 1500 feet deep all across central Greenland. The speculation in academia is that (what’s left of) the Jakobshavn will triple its retreat of the last ten twenty years in the next ten, moving into the interior of the ice sheet 30 miles. The amount of discharge with this fundamental shift in the way ice moves into the Icefjord, is still fairly poorly understood, but the simple fact that the Icefjord can be fed from there different directions instead, is concerning.