A new study has found that a mix of sea ice and icebergs bonded together (ice mélange) in the front of the tidewater Jakobshavn Isbræ, commonly known as Iluissiatt glacier (which literally means icebergs,) weakens before a major calving event at the earth’s largest and fastest-moving ice stream.
The icebergs that flow as one semi-rigid unit in the fjord are disrupted and break apart within minutes due to the buckling of the melange that is close to four miles wide and extends 20 miles to Disko Bay. The abrupt warming of the climate in the Arctic damages and melts sea ice making this phenomenon even more worrying for the world’s coastlines.
The failure of this iceberg dam allows more ice to calve into Ilulissat Ice Fjord than otherwise would have, and the icebergs eventually flow into the Atlantic. Of all the melting of Greenland contributing to sea-level rise, Ilulissat contributes 6.5 percent.
It is believed that “changes in ocean tides, the subglacial discharge of meltwater, and winds may help explain the sudden relaxation of the thick aggregate of icebergs pushing back against the glacier.”
The icebergs from Ilulissat are believed to have sunk the Titanic over 100 years ago in the North Atlantic.
A moulin is a portal where meltwater rivers plunge to the vast depths at the base of the Greenland ice sheet.
Shortly before Jakobshavn Isbræ, a tidewater glacier in Greenland, calves massive chunks of ice into the ocean, there’s a sudden change in the slushy collection of icebergs floating along the glacier’s terminus, according to a new paper led by authors at the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder, Emory University, and University of Alaska Southeast. The work, published in Nature Geoscience, shows that a relaxation in the thick aggregate of icebergs floating at the glacier-ocean boundary occurs up to an hour before calving events. This finding may help scientists better understand future sea-level rise scenarios and could also help them predict when major episodes of calving are about to occur.
In winter months, icebergs and sea ice accumulate within the fjord in front of Jakobshavn Isbræ, forming a frozen plug that prevents calving. The glacier can continue to flow into the fjord, intact, and advance dozens of meters each day. This accumulation of icy material, which scientists refer to as ice mélange, persists into the summer, but its shelf-like structure loses rigidity in the relative warmth, and it behaves more like individual icebergs jammed together in the fjord. Until now, no study has shown whether this type of late summer ice mélange can influence iceberg calving.
“It only takes a small bit of strain for the mélange to stretch or relax a little bit, and so it’s no longer an ice jam,” said Ryan Cassotto, a researcher in CIRES’ Earth Science and Observation Center and lead author of the new study.
To understand what was happening during these calving events, Cassotto and his colleagues took ground-based radar interferometers to Greenland in 2012 and set them up in Jakobshavn Isbræ’s proglacial fjord to record iceberg interactions every three minutes. They found that in between calving events, icebergs within the ice mélange moved together, flowing down the fjord as a single, cohesive unit.
But the movement of individual icebergs changed just before each of the 14 calving events that they observed––instead of flowing as a single, coherent unit, the ice mélange relaxed and icebergs began to move independently of each other.
“When the ice mélange relaxes, individual icebergs begin to rotate around, and when they begin to rotate around, the mélange loses its structure,” said Cassotto. “And when it loses its structure, it loses its ability to impede calving.”
Calving event at Jakobshavn Isbræ with tsunami.
Richard Heinberg writes an opinion piece on sapiens life-ending science experiment — The Most Colossal Planning Failure in Human History
Here’s the essence of our planning failure: we have built up civilization to a scale that can temporarily be supported by finite and polluting energy sources, and we have simply assumed that this scale of activity can continue to be supported by other energy sources that haven’t yet been developed or substantially deployed. Further, we have incorporated limitless growth into the requirements for civilization’s success and maintenance—despite the overwhelming likelihood that growth can occur for only a historically brief interval.
Failing to plan is often the equivalent of planning to fail. Planning is a function of language and reason—of which we humans are certainly capable. We plan all sorts of things, from weddings to the construction of giant hydroelectric dams. Yet we are also subject to cognitive dysfunctions—denial and delusion—which seem to plague our thinking when it comes to issues of population and consumption, and their implications for the future. In effect, we have collectively bet our fate on the vague hope that “somebody will come up with something.”
Heinberg, in his conclusion, writes:
It’s gob-smacking to think that such a planning process actually could have started as early as 70 years ago, and that, at this late date, it has still barely begun. Instead, today’s policy makers mostly just extrapolate PV price trends, hope for further technological improvements, and assume that huge systems for supplying society’s needs using renewable energy rather than fossil fuels will somehow self-assemble in an optimum way and at full scale—all in just a couple of decades.
Without planning, it just won’t happen.
Tsunami from calving icebergs is becoming an increasing threat to the Arctic’s coastal communities.
Those who have not seen the film Chasing Ice, which centers on the largest iceberg calving ever caught on video, should take a few minutes to watch this clip from 2012. It is jaw-dropping in its intensity coupled with a primal fear for our near-term future.
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