May 21, 2012

Deming Glacier Icefall Decline

Posted by Mauri Pelto

This is the first of two posts focusing on Deming Glacier and will focus on the Deming Glacier Icefall, the next on the Deming Glacier terminus. The glacier drains from the southwest side of the summit of Mount Baker a stratovolcano in the North Cascades of Washington, with a massive icefall feeding the lower valley terminus reach of the glacier.The icefall begins at 2200 meters and descends to 1600 meters. The glacier feeds the Middle Fork Nooksack River which provides some of the water supply for Bellingham, WA. I first observed the Deming Icefall from the terminus area of the glacier in 1987. This visit demonstrated that it is not safe to hike to the terminus of this glacier each year. In 1990 we began annual observation of Deming Glacier. Each summer we monitor the adjacent Easton Glacier in detail as the surrogate for Deming Glacier, which is dangerous and difficult to work on. Annual observation of the change in areal extent of the Deming Glacier with elevation combined with mass balance assessment on Easton Glacier provides an annual assessment of the meltwater provided by the glacier to the Nooksack River system. The glacier advanced from 1950-1980, and has retreated since 1980. The icefall transitions the glacier from the accumulation zone to the ablation (melt) zone at the bottom of the icefall. Above the icefall at 2400-3000 meters the average snow depth left at the end of the summer based on several thousand crevasse stratigraphy measurements is 2.75 meters(Pelto and Brown,2012). The icefall sweeps around a bedrock with an east and a west arm splitting above and rejoining below the knob. In particular the east arm has experienced significant reduction in width and velocity.The sequence below starts with an Austin Post photograph from 1979, that illustrates the east arm, the west arm is hidden. The east arm has the same width descending the step of the icefall. This is followed by the icefall in 1988, the red arrow indicates a rib that begins to extend across the east arm as the glacier thins.
The rib continues to extend across the east arm as noted from our observations of the glacier from an observation point adjacent to the icefall. Views from this location from 2003, 2005, 2007, 2009 and 2011 are shown in that order below. .
The next sequence examines the change in the icefall from Google Earth annotated imagery. The sequence begins with the 1984 map, the east arm is a nearly uniform 400 m in width. The sequence continues with 1993 and 2009. The red path is from 1993, and the blue path from 2009. In 1984 there is no bedrock rib, by 1993 it has begun to form but extends only 75 meters, by 2009 it extends 150 meters and by 2011 175 meters across the east arm. The width of the east arm has been reduced from 400 meters to 150 meters from 1984-2011. The sequence also indicates the lateral reduction in width after the two glaciers join at the base of the icefall from 1984 to 2009. In 1984 the glacier was 425 meters wide and in 2009 is 225 meters wide.