June 25, 2015

Rutor Glacier, Italy Retreat and Rising Snowline

Posted by Mauri Pelto

The Rutor (Ruitor) Glacier is one of the 10 largest in Italy and is on the France-Italy border draining into the Aosta River valley.  The glacier has three termini with the main terminus being the eastern one. The position of the glacier snout has been surveyed though not every year by the Italian Glaciological Committee since 1900. The glacier has a long series of terminus and volume observations compiled by Villa et al (2007) at the University of Milano-Bicocca, that indicate a 27% loss in area from the LIA maximum in the mid 19th century to 1975.  The glacier than increased slightly (1%) to 1988, followed by a loss of 5% from 1988 to 2004 (Villa et al, 2007). They further observe that the equilibrium line altitude (height of snowline at end of summer) was 2775 m during the Little Ice Age and 2850 m during the 1975-1992 period. Here we examine landsat imagery from 1988 to 2014 to identify the current trend in both ELA and terminus change.
ruitor ge 2011
Google Earth image indicating the three terminus of the Rutor glacier, arrows indicate 1988 terminus position, dots the 2011 terminus position of each.

In 1988 the eastern terminus, green arrow, had expanded slightly occupying the same location as it had in 1975, this left a trimline do the lack of retreat from 1975 to 1991, the area down valley had been deglaciated an additional 20 years. All three termini descended below 2600 m in 1988. The eastern and central terminus (yellow arrow) were separated by only 400 m. There was a small nunatak shortly above the terminus between the central and western (pink arrow) terminus. By 2014 a lake, red arrow, has formed due to retreat of the eastern terminus. The retreat is 500 m. Additionally between the eastern and central terminus the glacier margin has pulled back from a series of bedrock knobs. The central terminus, yellow arrow, has receded 400 m, and no longer reaches the lower slope foreland below 2650 m. The nunatak between the central and western terminus is now a substantial bedrock knob beyond the glacier margin. the western terminus has receded the least 300 m, but this is a greater percentage of the full length of the glacier feeding this terminus. Further there is negligible retained snowpack in 2014. The 2011 Google Earth image has stagnant areas evident at the terminus, red arrows, that lack of crevassing or other features of movement.

The snowline in 2014, red dots, extends east and west from a prominent rib, and is at 3000-3050 m. In 2011  the snowline is at 3050 m-3100 m and in 2013 the snowline is at 2950-3000 m.  The average snowline of the last four years is 150 -200 m higher than during the 1975-1991 period and 250 m higher than during the LIA.  This is substantial and will drive further continued rapid retreat.  This is the same climate that is driving retreat throughout the Alps from Verra Grande Glacier to Sabbione Glacier to Presena Glacier, that needed a blanket.

rutor Glacier 1988
1988 Landsat image
rutor Glacier 2014
2014 Landsat image
ruitor terminus
Google Earth image of new lake formed and retreat of eastern terminus
rutor 2011
2011 Landsat image

rutor 2013
2013 Landsat image