February 18, 2019
Boulder Glacier terminus position 1980-2018 as measured in the field. Note Lahar path that descends from Sherman Crater. Lahars have also occurred subglacially during our field observations.
Boulder Glacier flows down the east side of Mount Baker a strato volcano in the North Cascades of Washington. This steep glacier responds quickly to climate change and after retreating more than 2 kilometers from its Little Ice Age Maximum, it began to advance in the 1950’s as observed by William Long (Pelto, 1993). The glacier advance had ceased by 1979. From 1988-2008 we (NCGCP) have visited this glacier at least every five years recording its changes.
In 1988 the glacier had retreated only 25 meters from its furthest advance of the 1950-1979 period. The advance moraine was a well defined ridge, with a diversity of plant life just beyond the moraine. By 1993 the glacier had retreated 100 m from this position. At this time the lower 500 meters of the glacier was clearly stagnant. By 2003 the glacier had retreated an additional 300 m. In 2008 the glacier had retreated 490 meters from its 1980 advance position, a rate of 16 meters per year. The glacier as seen in 2008 despite the steep slope has few crevasses in the debris covered lower 400 meters of the glacier. This indicates this section of the glacier is stagnant and will continue to melt away. The transition to active ice is at the base of the icefall on the right-north side of the glacier. Below is the glacier in 1993 note the darkened cliff at adjacent to and right of the terminus. The picture below that is from 1998 again note cliff, than in 2003 from the same location as the 1993. Than an image from 2008 of the terminus from further upvalley, as it is not clearly in view from the previous location. The picture from Asahel Curtis taken in 1908 illustrates the width of the active glacier in the zone where it terminates in the 1990’s. The 2017 image illustrates the debris band from the lahar. Retreat from 1980-2018 has averaged 730 m, with the rate being relatively consistent. The retreat amounts to 20% of the total glacier length lost and the terminus elevation has increased by ~175 m. This glacier after nearly 40 years of retreat is still not approaching equilibrium and will continue to retreat. There is active crevassing closer to the current terminus than at any point since our observations began suggesting the retreat could slow in the near future. Note the 2015 LIDAR image from the Washington DNR, red path is the terminus. During he 2013-2018 period the end of summer snowline has been particularly high averaging ~2100 m. This is a reflection of continued negative mass balance as measured on the adjacent Easton Glacier. Boulder Glacier does respond fast to climate change, and the climate has not been good for this glacier. The glacier does have a consistent accumulation zone and can survive current climate (Pelto, 2010). For 35 years the North Cascade Glacier Climate Project has focused on observing the response of glaciers to climate change and will continue to do so.
Picture from August, 1993 of the terminus of Boulder Glacier
Picture from August 1998 of the terminus of Boulder Glacier
Picture from August 2003 of the terminus of Boulder Glacier
Boulder Glacier in August 2008.
Asahel Curtis image of Boulder Glacier in 1908.
Boulder Glacier in 2017 from Rainbow Ridge, taken by Tom Hammond
LIDAR image of Boulder Glacier from 2015 note the crevassing close to the terminus, red line.