Glacier Calving

Terminus of Columbia Glacier in 2005, showing the 300 foot ice cliff standing above the water. The ice extends another 1500 feet below the water to the ocean floor. Alaska’s Columbia Glacier, which spills into Prince William Sound, continues to retreat at a rapid pace, as scientists strive to better understand the dynamics between iceberg calving, glacier sliding, and the ocean water that the glacier flows into. As the glacier moves into the water—at a current rate of about 16 meters per day—it loses mass by calving at a higher rate, causing a significant retreat that’s been documented since the late 1907s.

Columbia Glacier Terminus, June 2008.

The University of Colorado’s Dr. Tad Pfeffer and a research team are documenting the glacier’s activity through field work and a photogrammetric study as part of a comprehensive NSF-funded project while public outreach (via the Extreme Ice Survey) is supported by a variety of sponsors, including NSF, NASA, National Geographic, and Nikon. In addition to documenting the rates of retreat, the team is filming time lapse sequences, and using photogrammetry and seismology to delve into the relationships between oceanography, calving, and the role those two processes have in accelerating the glacier’s disappearance.

Helicopter pilot Jim Harvey (Air Logistics) moving sling loads at Columbia Glacier, June 2004

The Columbia Glacier isn’t shrinking just because the ice is melting, the cause of retreat in landlocked glaciers. Rather, the Columbia, and other ocean-ending glaciers around the world, are winnowing down because they dump (or calve) enormous quantities of ice into the ocean. To date, scientists have only a vague understanding of the complex dynamics that occur between calving glaciers and the saltwater that laps at their bases, said Pfeffer. Decoding that relationship could dramatically increase the accuracy of rising sea level predictions.

Heavy crevassing showing accelerated flow above the marine-grounded fiord, Columbia Glacier, June 2008

“We don’t have a really robust way of writing down how calving works in quantitive physical terms we can put into a numerical model,” said Pfeffer. “Calving is a very complicated process. We’re still at the point of trying to understand exactly what’s happening.”

So far scientists know that calving outlet glaciers act to drain glacier and ice sheet interiors when accelerated flow upstream accompanies increased calving and flow at the terminus. Calving and increased flow speed, both naturally-occurring processes, can accelerate if the ice at the tidewater melts, thins, and loses contact with the bed. Simultaneously, the ice higher on the glacier can also speed up and thin. Though scientists don’t understand exactly how and why this occurs, they know it results in a cycle of acceleration, thinning, and more acceleration.

“Something about how the glacier interacts with the ocean affects it higher up,” said Pfeffer. “That is one of the mysteries we would really like to solve.”

Evidence shows a history of retreat among the Alaskan tidewater glaciers. For instance, since it began retreating in 1982, the Columbia glacier has backtracked 11 miles, about half the length of the fjord it occupies. In addition the glacier has shrunk from its 1982 size of 1,000 square kilometers and 60 kilometers long to 750 square kilometers and 42 kilometers long, and has lost an average of about four cubic kilometers per year since 1982 through calving.

Pfeffer said this process, while a naturally-occurring phenomenon, is likely triggered by climate warming and then perpetuated by natural cycles. If he and other researchers can quantify the physics of what’s happening in a computer model, they would contribute a more effective and accurate way to predict sea level rise as calving retreat continues to increase, not only in Alaska, but elsewhere in the world, including the major glaciers draining Greenland and Antarctica.

“Calving has become something that people recognize as very important because it is a very effective way of reducing glacial volume, and one that can be triggered by climate change but not controlled by it,” said Pfeffer.

Extreme Ice Survey team members Michael Brown and Jeff Orlowski fiming for the NOVA/National Geographic program Extreme Ice, June 2008

To continue the search for an explanation, Pfeffer and his team will return to the Columbia Glacier in late August to continue the field work and photography. In addition to the measurements, the team will also employ airborne radar bed profiling, time-lapse photography and GPS to help elucidate the complicated tidewater/glacial dynamics.