History On Ice
New insights from reviewing 60 years of crevasse research
Deep in the bowels of the University of Colorado Boulder library, William “Liam” Colgan dug through dust-covered documents and long-forgotten papers. It was a big change from how the CIRES research associate normally does research, digging through snow and ice out on the Greenland Ice Sheet. The American Geophysical Union invited Colgan and six team members, including CIRES director Waleed Abdalati, to compile and synthesize decades worth of research on glacier crevasses to highlight overarching key concepts and new research directions. Their review paper has just been published in this month’s issue of Reviews of Geophysics.
In mining studies from the 1950s up to the modern day, the team found a couple of surprises. The analysis shows that crevasses can fracture in several different ways, not just one, which changes the way scientists think about the physics of crevasses and how they model the future of big ice sheets. Additionally, crevasses usually form 40 feet below the surface, not at top, as had been previously believed. That could mean “buried” crevasses––those not reaching the surface––should be interpreted as very young, rather than very old. These and other findings are critical for understanding ice sheets and glaciers, not to mention their effects on sea level rise in a warmer world, said Colgan. “Understanding how and why ice breaks apart is important.”
Colgan, who is also an assistant professor at the Lassonde School of Engineering at York University, hopes his team’s study will serve as the most authoritative source for information on the topic of crevasses. The team––comprised of four men and three women––surveyed as many crevasse studies as they could find from the last 60 years, far sites as remote as Greenland and Antarctica. “The earliest meaningful crevasse studies are from the U.S. Army,” says Colgan. “They went out on the Greenland Ice Sheet during the Cold War. They had completely different motivation for understanding glaciers, and they were engineers not glaciologists, but their observations were exceedingly detailed and unique.” The team also pulled from more recent research, up to the present day, including studies from just last year, which examine crevasses in floating ice shelves.
While the paper defines and distinguishes between many different types of crevasses, based on where and how they form, at the most basic level, a crevasse is a brittle fracture where the ice has opened up and the two sides of that fracture are no longer touching. Today, organizations like the Air National Guard and the National Science Foundation want to understand how and where crevasses form for operational reasons: If you’re out there on the ice, you want to make sure a crevasse isn’t going to open up underneath you or equipment.
Scientists also want to understand them in the context of climate change and in relation to something called glacier mass balance—the health of a glacier defined as the difference between how much mass the glacier gains each winter versus melts in summer. Crevasses have a big influence on glacier mass balance. For example, they can cause glaciers to absorb more solar radiation or they can warm up glacier by allowing warm water to get deeper into the ice,making it flow faster. For the first time, the review paper describes and illustrates all these crevasse processes that affect glacier mass balance. It includes detailed figures that remap historical records of crevasse behavior. “Virtually all the old studies were based on an assumption that crevasses formed in one particular way,” Colgan said. But he and his team showed that there were multiple ways in which crevasses fractured, that they weren’t as static or uniform as once thought.
That is due, in no small part, to more advanced technology, says Mahsa Moussavi, a post-doctoral fellow with CIRES and one of Colgan’s colleagues on this paper. “We can see crevasses in more detail, both spatially and temporally,” she points out. “We can see how they develop and change through time and how fast they’re moving. And we can we see them from multiple perspectives.”
When it comes to climate change, that level of detail helped Colgan and his team describe and illustrate a list of unique ways that crevasses influence glacier mass balance. Warming air temperatures mean that the areas of glacier runoff zones, where more ice melts each summer than is replenished by winter snowfall, will get bigger. With that, more crevasses are expected to be exposed on glaciers around the world, which can trigger a variety of feedbacks with mass balance, including the warming and weakening of glaciers and ice sheets. That, in turn, could lead to faster ice flow into the ocean. “Looking forward, crevasses are the ultimate control of icebergs going into ocean, so caring about sea level rise means caring about crevasses,” says Colgan.
This story written by Laura Krantz.