A Blanket of Ice
1,500 miles long, 680 miles wide and up to 3,200 metres thick, the ice sheet runs coast-to-coast, covering all but a narrow fringe of Greenland’s western edge. Totalling some 1.8 million km2 (695, 000 square miles, this vast, white desert contains around 10% of the earth’s freshwater. If the entire ice sheet melted, the world’s oceans would rise by almost 7 metres (23 feet). The ice sheet forms a frozen record of the past, giving us an insight into the climate of both Greenland and the whole Earth.
Ice sheets have covered Greenland for the last 18 million years, though the ice that exists today is probably only 100,000 years old. It is formed by layer, upon layer, of compressed snow. The layers pile up, growing thicker and denser as the weight of new layers compresses the old into ice. The result of this weight, is that the ice sheet is moving, sliding slowly downhill by the force of gravity to the edges of the land.
MELT-WATER & MOULINS
During the summer months the ice sheet experiences long days of 24-hour sunlight. Much of this is reflected back, a process known as the albedo effect, but the suns warmth has some melting effect too. The surface of the ice sheet turns azure blue as giant melt-water lakes appear in the blinding expanse of white. Melt-pools may exist for many weeks and then suddenly vanish – the water draining away through cracks in the ice sheet, flowing down to the bedrock and lubricating the movement of the ice sheet from below. Sometimes the melt water flows with gravity, cutting channels like rivers across the ice sheet, disappearing suddenly down a plughole called a ‘moulin’.
As it reaches the edge of the island, the ice sheet increases in speed until it meets the coast and forms outlets such as glaciers, ice shelves and ice streams. As the ice moves over irregular terrain it forms crevices – deep cracks that can penetrate many metres. The speed of the ice sheet increases in pulses called surges, that can result in icebergs being ‘calved’ off into the sea.