March 31, 2011

Old Sun Glacier Glacier National Park slow retreat

Posted by Mauri Pelto

In Glacier National Park, MT all glaciers have been retreating. From 1850 to the present the number of glaciers has been reduced from 150 to 25. There are a few glacier such as Old Sun Glacier that have been retreating quite slowly since 1966 when the USGS maps were completed and are not disappearing anytime soon. Old Sun Glacier faces northeast and terminates at 8200 feet. This is a higher altitude than the rapidly shrinking Sperry Glacier, 7600 feet or Grinnell Glacier 6600 feet. A comparison of Google Earth images of Old Sun Glacier from the 1966 USGS map to 2009 indicate that the glacier has thinned and retreated but the majority of the glacier remains. The loss of area was noted as 12% from 1966-2005 and 14% by 2009. Below is the 1966 image, 1991 image, the strong brown line is the 1991 margin, 2003 image, 2005 image and the last two are 2009 images. The upper section of the glacier retains accumulation even in the poorest years such as 2009 and the glacier remains crevasses. The number of crevasses, slow recession and healthy accumulation zone point to a glacier that with present climate can be forecast to survive Pelto (2010). As long as a glacier maintains an accumulation zone it can survive at a reduced size. There are seven glaciers in Glacier National Park that have a consistent accumulation zone today each of these as a result is diminishing slowly,compared to the majority that have and will soon disappear.