“All Mt. Baker glaciers are significantly more extensive today than they were in 1950, refuting claims of disastrous, unprecedented glacier recession.” – Dr. Don J. Easterbrook
GLACIERS ON MT. BAKER, WA BEGIN TO ADVANCE
By Dr. Don J. Easterbrook
Recently the Seattle Times, Bellingham Herald, and other news media have published headline stories with claims by Maurice Pelto and others that glacier recession in the Cascade Mts. of Washington has been “disastrous” and “Glaciers across the North Cascades could lose 5 to 10 percent of their volume this year” “One scientist estimates the region’s glaciers are smaller than they have been in at least 4,000 years.” “The best word for it is disastrous.”
Photos and maps clearly show that the Mt. Baker glaciers reached their maximum extent of the past century in 1915 at the end of the 1880 to 1915 cold period. The glaciers then melted back strongly during the 1915 to 1950 warm period. The climate then turned cool again, and Mt. Baker glaciers advanced strongly for 30 years (1950-1980).
In 1977, the climate abruptly turned warm again and since about 1980, glaciers have been retreating. But they haven’t retreated as far upvalley as they did during the 1915-1950 warm period, even though the 1915-1950 retreat started much farther downvalley (i.e., the 1915-1950 warm period was much more robust than the 1978-2000 warm period, and most of the glacier retreat of the past century took place then).
These photos and maps prove that all Mt. Baker glaciers are significantly more extensive today than they were in 1950, refuting claims of disastrous, unprecedented glacier recession.
Temperatures in the western Cascades have been cooler by –2.5°F during the past decade and that seems to have halted ice retreat of at least some glaciers. Most of Mt Baker glaciers have response times of 3-8 years (time lag between climate change and response of the terminus) so this makes sense).
Pelto’s claim of Cascade glaciers losing 5-10% of their volume this year should result in noticeable retreat of glacial termini, so I examined photos of Roosevelt and Coleman glaciers (Fig. 3) on Mt. Baker, taken in 2009, 2011, 2013, and 2015 and was surprised to see that both glaciers had stopped retreating and had advanced slightly in the past several years.
The advance is not great, but it is significant because of the change from terminal recession to terminal advance. Documenting of other recent Mt. Baker glacier termini was not yet possible because of snow cover on the glacier termini that obscured the exact position of the glacier margins.
Figures 4 and 5 show the position of the terminus of the Roosevelt glacier in 2011 and 2013. Note the bare ground at the red arrow in 2011 and the same area covered by ice in 2013. Photos taken in 2015 show that this area continues to be covered with ice, which calves off the terminus at the cliff. Common reference points in both photos are shown by small arrow points.
Between 2011 and 2013, the glacier terminus advanced over bare ground. Photos in 2015 show that the terminus is still at the cliff edge.
Figures 6 and 7 show the position of the terminus of the Coleman glacier in 2011 and 2013. Note the bare ground at the red circles in 2011 and the same area covered by ice in 2013.Photos taken in 2015 show that the lobe of ice at the left margin of the glacier has moved downvalley even more.
Temperatures for the preceding decade
The cause of recent advance of the Roosevelt and Coleman glacier termini appears to be cooling in the western Cascades during the preceding decade. Temperatures recorded by NOAAin the western Cascades for the decade prior to the 2013 advance are shown in Fig. 8. The data show a cooling trend of –2.5°F per decade from 2003 to 2013.
Precipitation for the preceding decade
Winter snowfall also affects glacier behavior by conversion of snow to glacial ice. Winter snow packs in the Cascade Mts. since the 1980s have been generally positive even during the glacier recession, suggesting that temperature is more directly correlative with terminal activity.
Significance of the advance
The advance of the Roosevelt and Coleman glaciers shown on the 2013 photosare also seen on 2015 photos, despite a fairly warm summer in 2014 and low snowpack in the winter of 2014-2015.
Although the advance so far is quite small, it is significant because the advance has persisted for 2-3 years and shows a reversal of the recessional trend from the 1980s. The advance may or may not continue into the future―time will tell.
Dr. Don J. Easterbrook, Emeritus Professor of Geology, Western Washington University, Ph.D., Geology, University of Washington, Seattle, M.S., Geology, University of Washington, Seattle B.S., Geology, University of Washington, Seattle