March 2, 2018

Lower Curtis Glacier Annual Terminus Response to Climate Change

Posted by Mauri Pelto

Side view of Lower Curtis Glacier in 2013, 2015 and 2017, illustrating the reduced slope and height of glacier front in just four years.

Terminus observations have been reported to the WGMS from 2500 glaciers with 46,500 specific observations since the late 19th century, which you can explore with the glacier viewer application. Here we examine what it looks like to report from a glacier each year.  I have visited this glacier 34 consecutive years, each time camping in a tent near the glacier, a fun spot indeed when the weather cooperates. The Lower Curtis Glacier is an avalanche fed cirque glacier on Mount Shuksan in the North Cascades of Washington. It is a south facing and low elevation glacier for the range. This is an unusual combination that is supported by the heavy accumulation via avalanching from the upper slopes of Mount Shuksan. The glacier displays a magnificent set of annual layers in its terminus tongue. The terminus tongue is a spectacular wall of seracs that quickly rises 55 m above the bedrock. There are typically 50 layers visible indicating that this most of the ice in the glacier is 50 years of less in age.

Lower Curtis Glacier Front in 2007 and 2017 taken from same location.  Both retreat and thinning of the front in the decade is evident. 

From 1908 to 1950 the glacier retreated from the valley bottom into the cirque. The glacier advanced from 1950-1985 down slope and has retreated since.  Each year we survey the terminus location, measure the mass balance and survey the glacier surface elevation on a cross profile. Here we report on the annual terminus survey from 2007-2017.  The frontal change reported to the World Glacier Monitoring Service has been 2007=-13 m, 2008=-17 m, 2009=-20 m, 2010=-7 m, 2011=-5 m, 2012=-6 m, 2013=-5 m, 2014=-12 m, 2015=16 m, 2016=-16 m and 2017=12 m. This is a total of 129 m of retreat in 11 years, nearly 12 m per year. A longitudinal profile up the middle of the glacier indicates that it thinned 30 meters from 1908-1984 and 22 m from 1985-2016. Because of its heavy accumulation via avalanching the glacier moves rapidly and is quite crevassed at the terminus with large high seracs at the glacier front. In 2007 the height of the terminus seracs was 45 m, by 2014 the seracs were 37 m high and in 2017 had shrunk to 26 m high and not as steep.  The imposing tongue has certainly diminished. The glacier retreat fits the pattern in the region, with all Mount Baker a glaciers retreating (Pelto, 2015).