Ice researchers use data from the DLR-operated TerraSAR-X Earth observation satellite
Two gigantic cracks have formed in Pine Island Glacier, the longest and fastest-flowing glacier in the Antarctic. A new iceberg with an area of over 720 square kilometres and its smaller 'brother' separated from the glacier on 8 July 2013 and have 'calved' into the Amundsen Sea, off the west coast of Antarctica. Images acquired by the TerraSAR-X Earth observation satellite, operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), documented the gradual propagation of the first crack over a period of several months. On 11 May 2012, a second crack was discovered. Glaciologists can use this data to better understand the processes involved in the calving of icebergs.
A large iceberg, and a 'little brother'
NASA researchers discovered the crack in the glacier during an aircraft overflight on 14 October 2011. At that time, the crack was about 24 kilometres long and 50 metres wide. "The main iceberg that calved from the flowing part of the glacier is almost as big as Hamburg," says Angelika Humbert, an ice researcher at the Alfred Wegener Institute in Bremerhaven. The glaciologist and her team have used high-resolution radar images obtained with the TerraSAR-X Earth observation satellite operated by DLR to monitor the propagation of the crack and gain a better understanding of what was happening. Dana Floricioiu, from the DLR Remote Sensing Technology Institute, has been monitoring this crack on the Pine Island Glacier since the very beginning, and has derived valuable data such as the velocity field of the glacier. "Above this crack, the glacier was most recently flowing at a rate of 12 metres per day," reports Floricioiu. "The second crack was discovered in May, and this gave rise to an additional, 30-square-kilometre iceberg that has moved into the polar ocean along with its 'big brother'," continues Humbert.
Glaciers are constantly moving, flowing and cracking
Because glaciers are constantly in motion and have their own flow dynamics and highly complex geometry that is subject to continuous stress, the calving process is to a large extent still unexplored. "We are dealing with a material that is capable of both flowing and cracking. The interaction of these processes ultimately caused the floating icebergs to break loose," explains Humbert. The researchers have fed data from TerraSAR-X into computer simulations in which the flow and fracture mechanics of ice sheets can be modelled using numerical techniques. "We are incorporating the crack into our virtual ice shelf and then calculating the flow characteristics of the glacier. We pass these results to our partners at the Technical University of Kaiserslautern, who then simulate the crack propagation," explains Humbert.
A comparison with the latest satellite imagery shows researchers the extent to which their simulation reflects the real situation. Shortly before the 'birth' of the new iceberg, the crack on Pine Island Glacier was 28 kilometres long and 540 metres wide.
Ice shelves develop where glaciers flow into the sea. Glaciers are fast-moving masses of ice. An ice shelf is still connected to its ice sheet, but floats on the surface of the sea. With a thickness of several hundred metres, an ice shelf is much 'thinner' than the ice sheet that formed it, large sections of which are frozen to the rocky ground and can be up to four kilometres thick. The unusual feature of western Antarctica is that large areas of this ground lie below sea level.
Warm ocean water moves under the ice shelf
Angelika Humbert does not see a direct link to global warming. Instead, she believes that the formation of cracks in ice shelves and the resulting creation of new icebergs are natural processes. Pine Island Glacier is the fastest flowing glacier in the western Antarctic, but the polar researcher believes that this is due not so much to rising air temperatures as to changes in prevailing wind directions over the Amundsen Sea. These winds cause warm ocean water to move under the shelf ice which, in time, causes melting of the critical transition point between floating and grounded ice. "It is therefore possible that the western Antarctic could become unstable," suggests Humbert.
On 14 December 1911 a team led by the Norwegian Roald Amundsen was the first to reach the geographic South Pole. The Amundsen Sea, part of the South Polar Sea, bears the name of this pioneer of polar exploration. Pine Island Glacier flows from the Hudson Mountains into the Amundsen Sea; it calved for the first time in 2007.