Sortebræ and its tributary glaciers form an icy Pi symbol 

Today’s Image of the Day from NASA Earth Observatory features Sortebræ, a large tidewater-terminating glacier complex in East Greenland.

The image, captured in 1986 by the Thematic Mapper on Landsat 5, shows Sortebræ and several of its tributary glaciers creating a shape that resembles a pi symbol.

“Scientists consider about one percent of Earth’s 200,000 glaciers to be surging. This type of glacier goes through prolonged periods of quiescence and slow ice flow, when extra ice builds up at high elevations, followed by periods when ice lurches forward in a burst, in some cases flowing 10 to 100 times faster than normal for periods of months to years,” said NASA.

“Surges typically begin when excess meltwater builds up along the bottom of a glacier, lubricating the contact area between the glacier and ground and making it easier for the glacier to slide. Though it varies by glacier, surges usually last fewer than two years and occur every 15 to 100 years.”

“Changes during surges can be dramatic, especially when glaciers flow into the ocean. When this happens, extra water infiltrates the land-ice interface, allowing the glacier to slide even faster, sometimes by tens of meters per day.”

According to NASA, when surges subside and marine-terminating glaciers enter the inactive part of the cycle, waves and tides can beat back the glaciers more quickly than they advanced. That’s what has happened in recent decades at Sortebræ, said NASA.

This glacier complex is known for undergoing significant surges, with major events recorded in the 1950s and again between 1992 and 1995. The glacier complex includes Sortebræ and Sortebræ West, two confluent valley glaciers, with Sortebræ West joining Sortebræ at an almost perpendicular angle approximately 18 kilometers inland from Kap Savary.

The area around Sortebræ features a variety of glacier types, from small cirque glaciers to large transection and valley glaciers, all deeply incised into Tertiary plateau basalts. Historical aerial photographs from as early as 1933 show the glacier with few surface crevasses and elongated moraine loops, indicative of its surge-type nature.

Image Credit: NASA Earth Observatory 

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