December 27, 2012
Roosevelt Glacier is on the northwest side of Mount Baker, Washington with its accumulation zone joined with the Coleman Glacier. My first visit to Roosevelt Glacier was in 1984, when the glacier had just completed a 30 year period of advance from 1949-1979. Since 1979 the glacier has been retreating, image below. This post examines Google Earth imagery from 1993, 2003 and 2009 along with field observations from the glacier. The purple line indicates the advance moraine that the glacier emplaced during the 1949-1979 period of advance. We mapped the location of this moraine in 1985, when it was still recent and very evident. The red line is from 1993, yellow line from 2003 and green line from 2009. In 1993 the area below the lip of lava flow cliff is thin and stagnant, cliff noted by purple arrow. By 2003 the glacier has retreated to the top of the cliff and by 2009 the glacier has pulled back from the edge of the cliff. By 2012 the lower glacier, viewed from the edge of the Coleman Glacier, is thin and uncrevassed in the lower 350 meters of the glacier, up to the red arrow. The glacier retreated 190 meters from 1979 to 1993 and 220 meters from 1993 to 2009. The rate of 14 m/year has been relatively consistent.
The glacier is fed by three principal accumulation zones: 1) A glacier tongue that descends from the summit plateau at 3200 meters, 2) an avalanche fed and direct snowfall region beneath the north ridge, at 2200 meters 3) an avalanche and direct snowfall fed region beneath the northwest face, at 2400 meters. The annual snowline has averaged 2150 meters on Roosevelt Glacier from 1984-2010, which has led to a similar retreat of 14 m/year and mass balance loss -0.52 m/year of all Mount Baker glaciers, Pelto and Brown (2012). Each summer we investigate the retained snow depth retained in the crevasse stratified exposures on Mount Baker in the 2400 meter range. Below are several images from this investigation. In the second image the magenta arrows indicate specific annual layers that have been retained. Typical thicknesses are 1.75 to 2.25 m. The next two images are from when we are in an icefall looking for the best exposure to measure the annual layer stratigraphic thickness. The behavior of this glacier parallels that of Deming Glacier, Boulder Glacier and Rainbow Glacier all on Mount Baker.