The ice tongue of the Jakobshavn Isbrae on Greenland’s west coast has retreated significantly in the last five years. At the same time, it has thinned and started to flow faster. These changes have been confirmed in processed SPOT 5 HRS imagery.

The town of Jakobshavn (Ilulíssat in Greenlandic) lies near the mouth of the eponymous fjord from where icebergs calve off the Jakobshavn Isbrae glacier into Disko Bay. A UNESCO world heritage site, this glacier is one of the largest on the Arctic ice sheet, discharging some 35 billion tonnes of ice into the sea every year, that is, 6 to 10 percent of the total mass of ice discharged into the Northern Hemisphere oceans. Jakobshavn Isbrae is now the world’s fastest-flowing glacier and is estimated to be responsible for 4 percent (0.06 mm) of the recent rise in sea level across the globe.
Since 2004, new ASTER and Landsat satellite data have revealed a clear break in the glacier’s advance. Its northern and southern sections are exhibiting different behaviour, with the ice streams driving the flow of ice to the calving front moving at different speeds. The rate of ice flow doubled between 1985 and 2006, from 17 metres to 35 metres per day. 
 
 
 

The main front, or ice tongue, where icebergs calve from the glacier has retreated 40 kilometres since 1850. But this process has not been constant. From 1850 to 1964, the tongue retreated about 0.3 km a year, speeding up slightly in 1929-1930. The front remained somewhat constant from 1964 to 2001 and then accelerated significantly, reaching a speed of 3 km per year from 2001 onwards. 
 
 

Spot 5, avec son instrument HRS a permis de cartographier précisément et en trois dimensions le glacier Jakobshavn. La comparaison effectuée au LEGOS du MNT, réalisé par l’Institut Géographique National à partir d’images Spot 5 HRS de 2007 avec un d’avril 2003, a fait apparaître une forte diminution de l’épaisseur du glacier entre les deux dates. De plus, la vélocité du glacier a pu être mesurée en comparant deux orthoimages HRS acquises à 10 jours d’intervalle. La vitesse d’écoulement du fleuve de glace principal a atteint au maximum 42.5 mètres par jour soit 15.5 km par an, ce qui fait bien du Jakobshavn Isbrae le glacier le plus rapide au monde.
 
 

CNES and Spot Image are currently building up a large archive of SPOT HRS imagery for the International Polar Year. An initial campaign in the Northern Hemisphere covered some 830,000 sq.km. of the polar regions. This project is funding production and distribution of DEMs to the international scientific community to support the study of changes in the polar ice sheets. 
 
The Antarctic campaign now underway is pursuing the ambitious objective of covering two million sq.km. of the ice sheet in an effort to give scientists a clearer picture of our changing planet.