Jakobshavn Glacier (), also known as Ilulissat Glacier (), is a large outlet glacier in West Greenland. It is located near the Greenlandic town of Ilulissat (colonial name in ) and ends at the sea in the Ilulissat Icefjord.
Jakobshavn Glacier drains 6.5% of the Greenland ice sheet and produces around 10% of all Greenland icebergs. Some 35 billion tonnes of icebergs calve off and pass out of the fjord every year. Icebergs breaking from the glacier are often so large (up to 1 km in height) that they are too tall to float down the fjord and lie stuck on the bottom of its shallower areas, sometimes for years, until they are broken up by the force of the glacier and icebergs further up the fjord. Studied for over 250 years, the Jakobshavn Glacier has helped develop modern understanding of climate change and icecap glaciology.
Ilulissat Icefjord () was declared a UNESCO World Heritage Site in 2004, in part because of the importance of the Jakobshavn Glacier in contributing to the current scientific understanding of anthropogenic climate change.
Name
Jakobshavn has been a name used for this glacier in scientific literature since 1853 when Danish geologist Hinrich Johannes Rink referred to it as Jakobshavn Isstrøm (Danish for Jakobshavn Ice Stream). It is sometimes referred to in the international scientific literature (by glaciologists) as Jakobshavn Isbræ glacier. Isbræ is Danish for glacier. It is also commonly known by the anglicised version, Jakobshavn Glacier.
The local name for this glacier is Sermeq Kujalleq, where "sermeq" is Greenlandic for 'glacier' and "kujalleq" means 'southern'. It lies south of the town Ilulissat (colonial name Jakobshavn). UNESCO's World Heritage Site website uses this name, in connection with mention of the Ilulissat Icefjord world heritage site, which includes the downstream end of the glacier.
There is evidence that people have inhabited the area around the glacier for up to 4000 years. The recently abandoned settlement of Sermermiut (which means 'place of the glacier people') lies just to the north of the glacier, much nearer than Ilulissat.
The glacier is sometimes referred to as Ilulissat Glacier. This form simply replaces Jakobshavn with Ilulissat because of the change in the name of the town.
Acceleration and retreat
Jakobshavn is one of the fastest moving glaciers, flowing at its terminus at speeds that used to be around per day but are over 45 metres (150 ft) per day when averaged annually, with summer speeds even higher (as measured 2012–2013). The speed of Jakobshavn Glacier varied between per year between 1992 and 2003. The ice stream's speed-up and near-doubling of ice flow from land into the ocean has increased the rate of sea level rise by about per year, or roughly 4 percent of the 20th century rate of sea level rise. Jakobshavn Isbrae retreated from 1850 to 1964, followed by a stationary front for 35 years. Jakobshavn has the highest mass flux of any glacier draining the Greenland Ice Sheet. The glacier terminus region also had a consistent velocity of per day (maximum of per day in the glacier center), from season to season and year to year, the glacier seemed to be in balance from 1955 to 1985. The position of this terminus fluctuated by around its annual mean position between 1950 and 1996. After 1997 the glacier began to accelerate and thin rapidly, reaching an average velocity of per day in the terminus region. On Jakobshavn, the acceleration began at the calving front and spread up-glacier in 1997 and up to inland by 2003. In 2012 a significant acceleration of Jakobshavn was observed, with summer speeds up to 4 times its speed in the 1990s, and average annual speeds of 3 times its 1990s speed. Movement reached more than 17,000 metres per year. Jakobshavn has afterwards slowed to near its pre-1997 speed, with the terminus retreat still occurring until 2015. In 2016, researchers found the water temperatures in its fjord had dropped to levels as cool as those in the 1980s. Airborne altimetry and satellite imagery show that until early 2019, this temperature drop likely caused the glacier to re-advance, slow down, and thicken (by over 100 feet from 2016 to 2018).