December 1, 2011

Mass balance 2011 North Cascades, Washington and Juneau Icefield, Alaska

Posted by Mauri Pelto

In the summer of 2011, the North Cascade Glacier Climate Project completed 430 measurements of snowpack on 10 glaciers using probing and crevasse stratigraphy. This is much less than our normal number because of the exceptionally deep snowpack. The probe we use was 5 meters long, beyond that only crevasses could be used. The mass balance was quite positive for the first time since 2002. The combination of a La Nina and a negative PDO almost always deliver a mass balance in the North Cascades, 9 of 11 times (Pelto, 2008). The March-May period was the coldest and wettest spring ever in the North Cascade region. Summer was also cool in the region. This led to positive balances ranging from +1.2 to +2.2 m, the first year with significant mass balance since 1999. The first image below is the preliminary mass balance map for the Lynch Glacier in 2011, indicating the measurement points, black dots, and the blue contour line is the snowline. The cumulative mass loss since 1984 is still 12 meters, or 20-30% of the total volume of these glaciers, second image below. . Below is the field season captured in images.
Fourteen hundred kilometers north the Juneau Icefield glaciers did not fare as well. As part of the Juneau Icefield Research Program mass balance measurements are made every summer on the Taku and Lemon Creek glaciers. This summer the program was headed by Jay Fleisher, the mass balance portion was spearheaded by Chris McNeil and Toby Dittrich, Portland Community College. Satellite imagery from Sept. 11, 2011 indicates the snowline at the end of the melt season was just over 1000 meters on Taku Glacier and nearly 1100 meters on Lemon Creek Glaciers. This is higher than average and indicates negative mass balances for both glaciers. Snowpit and probing measurements at 40 locations, will yield a more specific mass balance, than provided by the snowline. The snowline is quite similar to 2009 and 2010 with snowpack depths generally a bit lower, 2009 and 2010 were also negative mass balance years. The snowpits are typically 2-4 meters deep and quite an effort to dig, the image below is from Cathy Connor at University of Alaska Southeast. The cumulative mass balance loss since 1953 on Lemon Creek Glacier is 25 meters, 15 meters since 1984.