Larsen C – A giant in motion
The A68 iceberg has been making headlines again after calving from the Larsen-C in July 2017. What happened? It moved and shrunk minimally. And while that may not be unusual, it is still worth a blog post.
Close examination of satellite image sequences from the last two months reveals the striking events unfolding there. Remember, the 5800 square kilometre iceberg is seven times the size of Berlin and is permanently moving. The iceberg has collided repeatedly with the ice shelf, dislodging smaller pieces of ice.##markend##
Satellite images show the iceberg as it drifts away from the shelf. Its southern section is moving at a speed of around 330 metres per day, which has already carried it roughly 25 kilometres from the scarp. And that is very fast if you consider the sheer dimensions of the frozen giant. Nonetheless, it has lost barely any of its surface area in recent weeks. (Click here for the video with a GIF animation of the satellite images up to 20 September 2017.)
The 'Polar and Cold Regions' working group at the DLR Earth Observation Center will spend the coming years monitoring the fate of the iceberg and – above all – the Larsen-C ice shelf. Was A68 perhaps the start of a series of breaks, as observed several times in other areas of the Antarctic Peninsula? Will the ice shelf collapse or remain stable? How will the inland glaciers develop if the ice shelf does indeed disappear and the effect of its constriction lost?
Radar eyes see changes
Radar images acquired by the ESA satellite Sentinel-1 are particularly suitable for this kind of long-term observation, as they permit year-round monitoring through cloud cover and the polar night. What is more, Sentinel-1 is designed to map large expanses of terrain and is equipped with an extra wide swath mode – an 'imaging strip' with a width of 400 kilometres. However, the resolution does suffer under this additional imaging range. The German radar satellites TerraSAR-X and TanDEM-X are used for the highly accurate detection of individual cracks. We receive their data at our GARS O’Higgins station in the Antarctic.
Our satellite images provide a pin-point documentation of local changes over years, revealing the calving of icebergs, the speed of inland glaciers, and the development of the grounding line – the point at which the ice shelf detaches from the ground and the ice begins to float on the water. But despite this comprehensive data mapping from space, it will still take some time to obtain concluding answers. So we will have to be patient.