Jacobsen Glacier, BC Retreat

Jacobsen Glacier is part of the Monarch Icefield of the Coastal Range of British Columbia. VanLooy and Forster (2008) noted that the glacier retreated at a rate of 30 meters/year from 1974 to 1992 and 47 meters/year from 1992-2000. In this post we examine Landsat satellite imagery from 1992, 1994, 2010 and 2012 to illustrate the changes over the last two decades. There are three readily observable changes. The first, indicated by purple arrows, is the lateral recession 2.5 km upglacier of the current terminus. At this point the glacier was in contract with a proglacial lake. The lake shoreline has not changed from the 1992-1994 images, but the glacier margin is now 300 meters distant from the lake margin. The second change, indicated by yellow arrows, is of what was previously a secondary terminus that terminated in a small proglacial lake in 1992-1994. This small lake has turned into an embayment of the larger unnamed lake that the Jacobsen Glacier ends in. The secondary terminus has retreated 900 meters since 1992. The last change is the actual terminus retreat of Jacobsen glacier with the 1992 terminus indicated by the pink arrows and the 2012 terminus by the blue arrow on the northern margin. The retreat and lake expansion has been 1100 mters from 1992-2012, a rate of 55 meters/year, only a slight change from the 1990-2000 reported rate. The changes indicate a consistent mass balance loss that is typical of glaciers in the Coast Range from Lemon Creek Glacier to Bridge Glacier and Helm Glacier. The ongoing mass balance losses are resulting in substantial glacier area and volume losses ( Pelto, 2007; Scheifer et al, 2008).

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Bridge Glacier Retreat Acceleration, BC, Canada

Bridge Glacier is an 17 km long outlet glacier of the Lilloet Icefield in British Columbia. The glacier ends in a rapidly expanding glacial lake with 1100 meters of retreat from 2005-2010. This 200+ m per year retreat is a substantial acceleration over the observed retreat rate of 30 m per year from 1981-2005 by Allen and Smith (2007). They examined the dendrolchronology of Holocene advances of the glacier and found up to 2005 a 3.3 kilometer advance from the primary terminal moraine band, with the most extensive advances being early in the Little Ice Age. The glacier currently ends at 1400 m and in 2010 had a late summer snowline of 2000 m. . The glacier terminus in 1970 is shown in map form, and is indicated by a brown line. The 2003 terminus position from a Landsat image, second image, is next with a red line marking the terminus. The normal Google Earth image, third image, is from 2005 and has a green line. An image from Geoeye from August 2010, last image, terminus purple line indicates the rapid acceleration of retreat. Retreat from 1970-2003 was 48 m per year. The retreat from 2003 to 2010 is 1400 meters, 200 m per year. This continued retreat and area loss will lead to glacier runoff decline in summer. This is crucial to the large Bridge River Hydro complex. This complex managed by BC Hydro can produce 490 MW of power. Stahl et al (2008) note in their modeling study of the glacier that ,”The model results revealed that Bridge Glacier is significantly out of equilibrium with the current climate, and even when a continuation of current climate is assumed, the glacier decreases in area by 20% over the next 50 to100 years. This retreat is accompanied by a similar decreasein summer streamflow.” This parallels our findings on the Skykomish River in the North Cascades, Washington Pelto (2008) and Pelto (2011).