September 24, 2015

Bionnassay Glacier Terminus Tongue Detaches, Mont Blanc, France

Posted by Mauri Pelto

Bionnassay Glacier drains west from Dôme du Goûter and Aiguille de Bionnassay of the Mont Blanc Massif in France. The glacier has a heavily debris covered terminus and has experienced less retreat from 1980-2010 then other Mont Blance glaciers. Bionnassay retreated 200 m (Moreau et al , 2012), while Mer de Glace retreated 500 m in the interval 1998 to 2008. Gardent et al (2014) observed a 25% decline in the area of glaciers in the French Alps from 1970 to 2009, with the rate increasing significantly recently.  Bionnassay is now in rapid retreat as the stagnant terminus tongue is detached from the active glacier tongue.

bionnassay overview

Bionnassay Glacier.  Red arrow indicates terminus of stagnant region.  Yellow arrow indicates bedrock emerging that is separating stagnant terminus tongue.  Green arrow indicates lower limit of active glacier. 

In 1985 the glacier terminus is at the yellow arrow. The debris covered ice is crevassed and covers the entire region at the red and green arrow. Points B and C are ice covered and Point A has a small exposure of bedrock. In 1999 retreat from the yellow arrow is evident the glacier still covering the region at the red and green arrow. In 2001 Google Earth image the terminus is evident at the red arrow, the region at the green and yellow area are covered by glacier ice. In 2011 the terminus has retreated 180 m since 2001, bedrock has emerged at the green arrow, beginning to separate the stagnant debris covered terminus tongue. At the yellow arrow the crevassing has diminished greatly. In 2015 the terminus has retreated to the pink arrow. Bedrock has been exposed from below the glacier terminus tongue at the yellow arrow. The active glacier terminus is now at the green arrow. At Point B and C glacier thinning has led to marginal retreat and exposure of bedrock where there was glacier ice. At Point A the expanse of exposed bedrock has greatly expanded.  The retreat of the main glacier terminus is around 200 m.  However, the retreat to the newly emergent bedrock separating the glacier is 750 m.  The active terminus is now 1700 m from the 1985 terminus position at the green arrow.  In the next few years this will become a well defined terminus, as the lower stagnant zone melt away.

Bionnassay Glacier is just south of Taconnaz Glacier, which is also retreating.
bionnassay 1985
1985 Landsat image
bionnassay 1999
1999 Landsat image
bionnassay glacier ge 2001
2001 Google Earth Image
bionnassay glacier ge 2011
2011 Google Earth Image
bionnassay 2015
2015 Landsat image

500 m