Feature: Arctic Thaw

Measuring Change

Jakobshavn Glacier continues to provide surprises!

by | 4.7.2011 at 1:08pm
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Pallet of Equipment waiting to be loaded for move from Thule AFB to Kangerlussuaq AFB in Greenland. Photo credit J. Yungel, NASA

We have moved south! One of the many challenges of our Greenland survey is the need to switch bases in the midst of the season since Thule Air Force Base also serves as a staging location for a major resupply mission for many of the Arctic outposts.  The whole set up has to be packed up and redeployed to Kangerlussaq, a small town along southwestern Greenland of about 600 people located at the head of Sondre Stromfjord, a feature extending 90-100 miles out to the coast. The edge of the ice cap is about 10-15 miles to the east and glacially fed rivers run from the ice down to the fjord. Located on the site of a former cold-war era US Air Force base it serves as Greenland’s international airport.

The move involved packing up not only the personnel, but pallets of sensitive instruments and equipment, the base stations that were in place for calibration of the data etc.…a major effort!  However we have had a very successful first leg to the IceBridge mission while in Thule, with 8 successful sea ice flights (and 2 glacial flights), which was the main goal of the first part of the deployment. Moving south will also bring us closer to several of key glaciers we plan to monitor, including the Jakobshavn Glacier.

We should note that while we managed the relocation to Kangerlussuaq, we have had considerable delays in taking to the air again due to a series of propeller repairs needed on the P3.  The very cold temperatures, -28°C (-18°F) when we walked the 600 m over to the airport this morning, have been the cause of some of this.  Kangerlussuaq has no heated hanger so the plane sits outside in the cold, causing gaskets to contract and hydraulic fluid to leak out. However we are back flying and collecting impressive data!

Jakobshavn Glacier's heavily broken and crevassed surface as the rapidly moving ice deforms as it flows. Photo credit P. Spector

Our first return to the air was a survey of Jakobshavn Glacier, located about 250 km north of Kangerlussuaq on the west coast of Greenland.  Starting at the fjord where the glacier meets the sea, we worked inland for about 150 km with closely spaced lines near the coast and more widely spaced lines inland running an exact repeat of surveys done during the 2009 and 2010 IceBridge campaigns.  These repeat surveys are extremely important for some of the fast changing glaciers. For the Jakobshavn area once inland from the fjord and the coastal hills, the ice cap is flat with no obvious large-scale topography to show the location of the glacier that forms a fast flowing ice river though the ice cap.  However, once we cross over the glacier, the flat and somewhat featureless surface of the ice cap changes rapidly to a broken-up and crevassed surface as the rapidly moving ice deforms as it flows.

An image of the calving front of the Jakobshavn glacier using the Airborne Topographic Mapper (ATM), a laser used to determine changes in ice sheet elevation (the image shows a transition from the blue upper left area in the fjord back into the Greenland Ice Sheet). Image credit Rob Russell, NASA

Jakobshavn is a large and important glacier, draining over 6% of the Greenland ice cap and more potential sea level rise than any single source in the Northern Hemisphere. It is also one of the most rapidly changing glaciers in the world with thinning rates estimated at up to 15 meters per year. Jakobshavn over the last decade has followed a pattern of calving and retreating, and as recently as July 2010 suffered a significant retreat of ~1.5 km. This very active glacier is the subject of intense amounts of study, so flying the same survey lines several times allows us to determine the pattern of thinning over the entire glacier.  This is essential for understanding the processes at work.  A surprise result from first two years of IceBridge flights is that the thinning extends much further inland than had been suspected; in fact it extends beyond the limits of our survey.  As a result, a second mission to Jakobshavn is planned for this year to extend the survey inland an additional 75 km.  When those lines are reflown next year, we will have a more complete picture of the evolution of the glacier. It is findings such as this that have made IceBridge so key to helping us understand the changes in the polar regions.


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