easton glacier survey – From a Glaciers Perspective

Mass balance, terminus and supra glacial stream assessment are illustrated in the video, Filmed by Mauri Pelto, Jill Pelto, Melanie Gajewski, with music from Scott Powers.

This is the story of the annual monitoring of Easton Glacier, Washington. We have been monitoring Easton Glacier on Mount Baker, a stratovolcano in the North Cascade Range, Washington since 1990. Each year we survey the terminus position, measure its mass balance, assess crevasse depths and map surface elevation on a transect across the glacier. In 1990 Easton Glacier was in contact with an advance moraine built from the late 1950’s- 1980’s. The advance moraine is noted in the 2015 Washington DNR Lidar image of the terminus area by black arrows. The green arrows indicate the recessional moraine from the winter of 2015. Red arrows indicate the Little Ice Age lateral moraines Railroad Grade (RG) to the west and Metcalfe Moraine (MM) to the east. From 1990-2017 the glacier has retreated 370 m, including 65 m in the last three years. The second Lidar image indicates the transect where the surface elevation is mapped, red line. This is close to 2000 m in elevation, and in a good snow year retains snowpack and in most recent years has lost its snowpack (note paired image below). In 2015 the worst year, the snowpack had been lost by the end of July. Note the comparison of the 2017 transect snowpack and 2015 lack of snowpack.

Washington DNR Lidar image of Easton Glacier , black arrows indicate 1980’s advance moraine, green arrows 2015 winter moraine and red arrows the Little Ice Age lateral moraines. Blue dots indicate the glacier margin.

Washington DNR Lidar image of Easton Glacier. Blue dots indicate the glacier margin. Red line the cross glacier profile.

A view along the cross glacier profile at 2000 m in early August of 2015, snowpack gone already and in 2017 with 2 m of snowpack remaining.

More than 5000 measurements of snow depth and melt have been completed illustrating the glacier has lost 16.6 m of water equivalent thickness, over 18 m of thickness from 1990-2016. For a glacier that averaged 70 m in thickness in 1990 this is ~25% of the volume of the glacier gone. The glacier has not maintained sufficient snow cover at the end of the summer to have a positive mass balance, this is the accumulation area ratio. The mass balance and terminus data is reported annually to the World Glacier Monitoring Service. The area lost in the terminus region due to the retreat has been 0.22 km2.

The glacier has also slowed its movement as it has thinned, evidenced by a reduction in number of crevasses. In the lowest icefall Jill Pelto has surveyed the crevasse depths finding a mean depth 20 m and a maximum depth of 32 m. This glacier supplies runoff to Baker Lake and its associated hydropower projects. Our annual measurements here and on Rainbow Glacier and Lower Curtis Glacier in the same watershed provide a direct assessment of the contribution of glaciers to Baker Lake. The glacier is also adjacent to Deming Glacier, which supplies water to Bellingham, WA. The Deming is too difficult to access, and we use the Easton Glacier to understand timing and magnitude of glacier runoff from Deming Glacier. Deming Glacier has retreated a greater distance during this period, 705 m, but has lost a similar area.

Annual terminus survey in 2015 terminus exposed to melting by early July. In 2017 terminus being exposed first week in August. Taken from same location.

Crevasses measurement in lower icefall and on the cross profile. In both cases crevasse depth is measured, on the profile 2017 winter snow depth remaining measured.

Easton Terminus viewed from our benchmark location just beyond 1980’s margin. Tree in foreground is over 50 years old.

In August we will be making a detailed study of the Easton Glacier for the 23rd consecutive summer. Our main focus is measurement of snow depth and snow melt on the glacier. We will be mapping the terminus position and two profiles of the surface elevation across the glaciers at 1800 m and 1950 m. We will also examine two new bedrock knobs that have melted out in the midst of the glacier at 2050 m. The Easton Glacier is important as a water resource for the Baker lake and Baker River Hydropower system. This hydropower system is capable of producing 170 MW of power. The runoff from Easton Glacier would normally flow into the Baker River below Upper Baker Dam, however it is extracted from the normal stream and routed through a pipeline to enter Baker Lake and then produce power via Upper Baker Dam (second image), note yellow dots showing runoff pathway. The Easton Glacier retreated over 2 km from its Little Ice Age maximum to 1955. By 1965 the glacier was advancing, this advance ended in the early 1980’s and by 1987 retreat from the moraine was evident. Beginning in 1990 we have made an annual survey of the glacier terminus noting a retreat of 320 m from 1987-2010. The first image below is of Easton Glacier from 1912 the second from 2011 with the same locations highlighted. A prominent knob on the upper glacier has changed little, ocher arrow. The lower margin of the glacier on either side of the main Easton at the blue arrow and red arrow show substantial thinning and retreat. The purple arrow indicates the terminus change. The lower Easton Glacier has changed a great deal in the last 100 years, not the upper glacier. This is an indication of a glacier adjusting to climate change that is retaining an accumulation and can survive. The last image in the sequence indicates the Little Ice Age terminus yellow line, the 1993 terminus orange, 1998 terminus is purple, 2004 terminus is green and 2009 terminus is ochre.
In the above image the red arrows indicate the location of the two survey profiles we complete across the glacier. The green arrows indicate two locations of investigation for the summer, to the left is the top of the Deming Glacier Icefall that will visit and the right green arrow a new bedrock knob that emerged from beneath the glacier in 2009. A month from now we will be surveying the glacier covering the glacier top to bottom and side to side. We will be joned by Peter Sinclair who is going to use is videography skills to examine how we measure glacier change. The first image below is from Steph Abegg a superb climber and photographer who was with us in 2010 as part of Team Juicebox working on the Uncertain Ice documentary. The main goal of our research each year is assessing the glacier’s mass balance. This is the equivalent of its bank account, with snow accumulation being deposits and snow-ice melt being withdraws. We map the changes across the glacier and determine if the bank account grew or declined, 2011 map is below. Since 1990 the bank account has lost 10 meters of thickness of an average of 70 m total. Last year the glacier did gain over a meter. A key measure is the percent of the glacier in the accumulation zone (AAR), below 65% is a loss above a gain, bottom image. The 2012 winter was a La Nina which tends to lead to very good snowpack, the transition out of La Nina took place in late spring-early summer leading to greater melting than 2011, we will see in three weeks.