September 8, 2013
Conrad Icefield Retreat, Selkirk Mountains, British Columbia
Posted by Mauri Pelto
Comparison of Conrad Glacier (Cn), Malloy Glacier and Vowell Glacier (V) in Landsat images from 1987 and 2015. The 1987 terminus location indicated by red arrow, 2015 terminus position yellow arrow and upglacier thinning purple arrows.
Conrad Icefield is at the northern edge of the Bugaboos in the Purcell Range of the Selkirk Mountains in southwest British Columbia. The icefield feeds several terminus tongues primarily the Conrad Glacier and Malloy Glacier, both of these have two arms. In the case of Conrad Glacier the two arms still join above the terminus, while for Malloy Glacier there are now separate termini.
In 1987 Conrad Glacier terminus extends to the red arrow and no proglacial lake is present. Malloy Glacier south and west terminus both reach the shore of a small lake. By 2005 both the south and west terminus of Malloy Glacier have retreated from the lake shore. A closeup view of the Malloy Glacier terminus, red arrows, from 2005 indicates that the southern terminus is quite stagnant below the icefall and retreat is continuing. The west terminus is quite narrow and ending on a steep slope, with a buttress paralleling the north side of the terminus ending at the orange arrow.
The Conrad Glacier terminus is stagnant beyond the knob at Point A, and is only 200 meters wide from Point A to Point B. The proglacial lake beyond the Conrad Glacier terminus is now 400 m long and the terminus has just retreated upvalley of the lake. Conrad Glacier has retreated a significant distance from the proglacial lake, and now ends on a line between the knob at Point A and B. In 1987 the Conrad Glacier extended 1700 m after the two arms joined. In 2015 this distance is ~700 m. The upstream location of the joining has changed little, indicating a retreat of 950 m from 1987 to 2015. Another measure is the distance from where the two arms of Conrad Glacier join to the terminus. In 2015 Malloy Glacier western terminus is at the top of the buttress, orange arrow ending 300 m from the lake, yellow arrow. The southern terminus has pulled back 250-300 m from the lake. Malloy Glacier has undergone a 300 m retreat from 1987-2015. In 2013 Malloy Glacier western terminus is at the top of the buttress, orange arrow ending 250 m from the lake, pink arrow. The southern terminus has pulled back 250-300 m from the lake. Malloy Glacier has undergone a 250 m retreat from 1998-2013. Conrad Glacier has retreated a significant distance from the proglacial lake, and now ends on a line between the knob at Point A and B. The proglacial lake has filled in at its upstream end a small amount, hence the distance from the downstream end of the proglacial lake to Point A is a better measure of the retreat from 1998 to 2013. Images from Ben Pelto from 2015 indicate the lack of crevassing below the Conrad Glacier junction. This suggests retreat to this junction will occur in the near future.
Examination of the margins of both glaciers above the icefalls 1 km above the terminus in 2005 indicates thinning and downwasting, red arrows, suggesting reduced flow that will drive continued retreat. These glaciers are retreating faster than Bugaboo Glacier, but not as fast as Vowell Glacier also in the Bugaboos. The retreat observed in the southern interior ranges of British Columbia, has been 15% from 1985 to 2005 (Bolch, 2010).
British Columbia Topographic Map of the Conrad Icefield area
1998 Landsat image of Conrad Icefield
2005 Google Earth image of Malloy Glacier terminus
2005 Google Earth image of Conrad Glacier terminus
2013 Landsat image of the Conrad Icefield
Conrad Glacier Terminus in 2015 from Ben Pelto
Conrad Glacier margin 1 km above the terminus in 2015, Ben Pelto