Pine Island Glacier in West Antarctica’s highly vulnerable Amundsen Sea Embayment a 2014 rift was under study by satellite with seismic data taken from instruments on the ice shelf when a massive rift was found to have “shattered like glass” for 6.5 miles at 80 mph. If other rifts are doing the same, sea level rise could occur much faster than anyone had thought possible. Ice shelves provide the critical ability to cork the inland ice streams from dumping land ice into the ocean and raising sea levels across the world’s coastlines.
From the 2014 fracture study:
Hannah Hickey from the University of Washington writes the presser:
A critical question is how warmer oceans might cause glaciers to break apart more quickly. University of Washington researchers have demonstrated the fastest-known large-scale breakage along an Antarctic ice shelf. Their study, recently published in AGU Advances, shows that a 6.5-mile (10.5 kilometer) crack formed in 2012 on Pine Island Glacier—a retreating ice shelf that holds back the larger West Antarctic ice sheet—in about five and a half minutes. That means the rift opened at about 115 feet (35 meters) per second, or about 80 miles per hour.
“This is to our knowledge the fastest rift-opening event that’s ever been observed,” said lead author Stephanie Olinger, who did the work as part of her doctoral research at the UW and Harvard University, and is now a postdoctoral researcher at Stanford University. “This shows that under certain circumstances, an ice shelf can shatter. It tells us we need to look out for this type of behavior in the future, and it informs how we might go about describing these fractures in large-scale ice sheet models.”
A rift is a crack that passes all the way through the roughly 1,000 feet (300 meters) of floating ice for a typical Antarctic ice shelf. These cracks are the precursor to ice shelf calving, in which large chunks of ice break off a glacier and fall into the sea. Such events happen often at Pine Island Glacier—the iceberg observed in the study has long since separated from the continent.
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In other parts of Antarctica, rifts often develop over months or years. But it can happen more quickly in a fast-evolving landscape like Pine Island Glacier, where researchers believe the West Antarctic Ice Sheet has already passed a tipping point on its collapse into the ocean.
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“Is rift formation more like glass breaking or like Silly Putty being pulled apart? That was the question,” Olinger said. “Our calculations for this event show that it’s a lot more like glass breaking.”
If the ice were a simple brittle material, it should have shattered even faster, Olinger said. Further investigation pointed to the role of seawater. Seawater in the rifts holds the space open against the inward forces of the glacier. And since seawater has viscosity, surface tension and mass, it can’t just instantly fill the void. Instead, the pace at which seawater fills the opening crack helps slow the rift’s spread.
From the surface to the ocean bed:
Some snippets from the British Antarctic Survey show how a 1940 El Nino event began glacial retreat at Pine Island Glacier, Thwaites Glacier, and the rest of West Antarctica. The Amundsen Sea Embayment holds eleven feet of sea level rise.
From the lead authors of the British Antarctic Survey Study:
James Smith, a marine geologist at British Antarctic Survey said:
“Our previous work in 2016 provided the first direct evidence that neighbouring Pine Island Glacier started to retreat in the 1940s. However, that was just one glacier draining into the huge Amundsen Sea Embayment. Now that we know Thwaites glacier also started to retreat around the same time is really significant. It demonstrates that glaciers in this area were responding synchronously to an external climatic driver.”
“A significant implication of our findings is that once an ice sheet retreat is set in motion it can continue for decades, even if what started it gets no worse. It is possible that the changes we see today on Thwaites and Pine Island glaciers – and potentially across the entire Amundsen Sea Embayment – were essentially set in motion in the 1940s.”
Rachel Clark, lead author, said:
“What is especially important about our study is that this change is not random nor specific to one glacier. It is part of a larger context of a changing climate. You just can’t ignore what’s happening on this glacier.”
The 1940 El Nino-Claus-Dieter Hillenbrand, U.K. lead investigator of THOR and study co-author at British Antarctic Survey said:
“It is significant that El Niño only lasted a couple of years, but the two glaciers, Thwaites and Pine Island, remain in significant retreat. Once the system is kicked out of balance, the retreat is ongoing,” said corresponding author Julia Wellner, U.S. lead investigator of the Thwaites Offshore Research project, or THOR, an international collaboration whose team members are authors of the study.
“The finding that both Thwaites Glacier and Pine Island Glacier share a common history of thinning and retreat corroborates the view that ice loss in the Amundsen Sea sector of the West Antarctic ice sheet is predominantly controlled by external factors, involving changes in ocean and atmosphere circulation, rather than internal glacier dynamics or local changes, such as melting at the glacier bed or snow accumulation on the glacier surface.”
The 2014 crack generated some incredible animations.
