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. The first picture below provided by Richard Hodgkins to the PAGES project shows a century of change. Below that is the 2009 terminus view in Google Earth. The terminus is quite crevassed indicating considerable velocity. It is currently at the top of a steep slope that it has retreated up in the last five years. 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, data is not in for the 2006-2010 period but the retreat is in excess of 200 meters. The retreat has been triggered by sustained negative mass balance. A mass balance program on d’Argentiere was begun in 2004, the glacier lost 1.3 m in 2004, 1.9 m in 2005, 1.4 m in 2006, 0.7 m in 2007, 1.3 m in 2008 and 2.6 in 2009. That is a cumulative mass balance loss of 9.2 meters of water equivalent lost from the glacier in six years, and that is a 10-11 m loss in average ice thickness from the glacier. The recent rapid retreat and mass balances losses parallel those of the other glaciers in the Alps from which data is reported to the WGMS. 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. This will foster continued retreat. A view across the glacier in August 2008 from Jürg Alean indicates the meager snowcover on the south facing glaciers and the main glacier tongue.
Pingback: After a galcier retreated | See0800