September 16, 2014
Robson Glacier is the largest glacier on the highest mountain in the Canadian Rockies. The glacier begins at 3200 m and drains northeast from the summit ending in a proglacial lake at 1720 m. The glaciers upper west side has heavy avalanche accumulation from Mount Robson’s upper slopes, note the 1964 photograph from the legendary USGS glacier guru Austin Post. The history of this glacier has been examined using tree rings and lichenometry. Heusser (1954) observed that the glacier reached its Little Ice Age Maximum arond 1780 and had retreated at a rate of 2 m/year from then until 1908 and at a rate of 16 m/year from 1908-1953. The terminus history up to 2006 is summarized in a map from Roger Wheate (UNBC) and Laura Thomson that indicates, a minor retreat of 300 m from 1850 to 1922, a rapid retreat from 1922-1950 of 1200 m, a readvance from 150 to the 1980’s of 300 m and a resumed retreat of 500 m from the 1980s to 2005. Here we examine satellite imagery from 1987-2014 to see more recent changes.
Robson map from Wheate (2012)
Austin Post 1964 Photograph
In each image the red arrow indicates the 1987 terminus position, the yellow arrow the 2013 terminus position and the pink arrow a bedrock step on the east margin of the glacier. In 1987 the proglacial lake at the terminus is 350 m long. The bedrock step on the eastern margin is largely buried under the glacier and the snowline is at 2300 m though the melt season still has six weeks to go. In 1989 the terminus is not quite as wide and the snowline is at 2500 m. By 2002 the glacier has retreated 400 m with the proglacial lake having expanded into a new narrower section. The bedrock bench is more prominent adjacent to the glacier and now extends as a bare rock further into the main glacier. The snowline is at 2400 m. By 2006 the glacier has retreated an additional 100 m and the snowline is at 2500 m. There are two apparent bedrock ribs the upglacier one extends 300 m toward the glacier center from the east margin and the lower rib 150 m. This represents most of the flow from the eastern tributary of the glacier that extends only to 2800 m and has less avalanche contribution. By 2013 the glacier has retreated 700 m since 1987, a rate of 30 m/year. This is a more rapid rate than the retreat observed from 1908-1953.The snowline is just above 2500 m. In 2014 the terminus position is a bit obscured in this September image, the bedrock rib is more prominent than in 2006 and the snowline is again above 2500 m, with three weeks left in the melt season.
It is apparent that a zone of persistent and consistent accumulation remains above 2600 m on Robson Glacier, and that it can survive current climate change. The recent trends of a snowline above 2500 m indicates that retreat will continue in the near future in response to current climate. Both 2013 and 2014 have been warm summers leading to above average melt conditions that should lead to rapid thinning of the lower terminus tongue and rapid retreat in the next several years. Hopefully another satellite image will be obtained to indicate the end of season snowline (ELA). The retreat of the is glacier parallels that of Coleman Glacier just east of Mount Robson, Freshfield Glacier and Columbia Glacier.
1987 Landsat image