January 17, 2011
Glacier d’Argentiere (A) in Landsat images from 1990 at left and 2015 at right. The red arrow is the 1990 terminus and the yellow arrow the 2015 terminus. The purple arrow indicates a tributary that has detached. The black arrow in 2015 indicates the current icefall terminus. Mer de Glace is Point M.
Glacier d’Argentiere flows 9 km northwest towards the valley of Chamonix, France just north of Mont Blanc and one valley north of the Mer de Glace. The glacier retreated 1000 meters from 1870-1967. From 1968-1985 the glacier advanced 300 m. Since 1985 the glacier has been retreating at an increasing rate: 80 meters from 1991-1995, 187 meters from 1996-2000, 199 meters from 2001-2005, and 162 m from 2006-2010 (WGMS). The retreat has been triggered by sustained negative mass balance. A mass balance program on d’Argentiere indicates the glacier had a cumulative mass balance loss of 9.2 meters of water equivalent lost from the glacier from 2004-2009, that is a 10-11 m loss in average ice thickness from the glacier. Berthier et al (2014) mapped ice thickness changes in this region from 2003 to 2012 using the Pléiades satellites. They identify a negative region wide mass balance of glaciers in the Mont-Blanc area of -1.04 m/year for the 2003-2012 period, with thinning on Argentiere limited above the icefall and large below the icefall for the lower 1.5 km of the glacier, bottom image. The reason for the mass balance loss is evident from the Google Earth imagery of August, 2009. The snowline, shown in lime green, is at 3300 meters on south facing slopes and at 2900 meters on north facing slopes and the main valley of the glacier, this is one month left in the melt season. At this point the glacier is 35-40% snowcovered and will be less by the end of the melt season.To be in equilibrium a glacier must have 60% snowcover at the end of the summer. From 2004-2009 the average snowcovered area at the end of the melt season was 30%. The tributary glaciers draining the south facing slopes of the valley have lost all their snowcover in 2005, 2006 and 2009. This is leading to a diminished contribution to the mainstem of the Argentiere. The mainstem of the glacier has detached from the terminus tongue at the icefall at 2175 m, with the stagnant ice below extending 1.5 km to 1650 m. This detached tongue will now waste away. The retreat of the icefall terminus will likely be slow. In the short term the glacier will retreat faster than Mer De Glace as the stagnant tongue is lost. In the longer run terminus retreat should be less.
2009 Google Earth image of glacier and snowline in green
2009 Google Earth image of icefall terminus black arrows and stagnant ice blue arrows.
2009 Google Earth image indicating the 1.5 km stagnant ice tongue extending from the icefall terminus at the black arrow to the end of current ice, red arrow.
Figure illustrating thinning from 2003 to 2012 on Mer de Glace (M), Argentiere (A) and Pre de Bar (P). All have thinning p to the highest elevations. Mer de Glace has a much more extensive zone of high thinning more than 15 m.