Petermann has the largest floating ice shelf in the Northern Hemisphere so calving icebergs are not unusual, but ones of this size will have an impact. Floating ice shelves, or ice tongues as they are often called, are the ocean terminating ends of ice streams that move ice off the continent. The shelf serves as a control on the flow of the ice stream once it hits the water, through the buoyant force pushing back against the ice shelf front. The sudden reduction in shelf size changes the balance and can cause the glacier to accelerate.
The most dramatic pictures of the loss of ice show glaciers retreating up valleys, thinning as they go; because the whole glacial system is connected, thinning at the far end has a large impact on this process. Breaking off the tip changes the driving forces that control the flow of ice further upstream, and with continuing mass loss, the thinning and speeding up of ice are reaching further and further inland. This can affect a very large area, so it doesn’t take much thinning to add up to a significant volume of ice loss. For our flight that means extending our survey grid further inland, so we can record the present ice surface to be able to monitor any changes in the future. Today’s grid will be followed by another flight (weather cooperating!), and then matched with last year’s grid. The goal of the three missions is to complete a 10-km-grid over the entire catchment area of Petermann Glacier. Glaciers, like watersheds, are referred to with catchment areas, but glacier catchments with their powerful forces do not always follow watershed boundaries.