December 1, 2013
Bromley Glacier Retreat, NW British Columbia
Posted by Mauri Pelto
Bromley Glacier is the largest outlet glacier of the Cambria Icefield near Stewart, BC. The glacier drains north into the Bear River. Dan Smith and his graduate students of the University of Victoria have been busy searching for fossil wood as it emerges from beneath the rapidly retreating glaciers of British Columbia. They have found numerous pieces from former forest that have emerged in the last decade after being buried for at least 2000 years. Smith, points out this is due to the rapid retreat that began in the area in the 1980’s. Bolch et al (2010) noted a reduction of 0.3% per year in glacier area in the Northern Coast Mountains of British Columbia from 1985 to 2005. Scheifer et al (2007) noted an annual thinning rate of 0.8 meters/year from 1985-1999. One of the glacier they visited was Bromley Glacier in 2011. This led to a publication from Smith and Kira Hoffman (Hoffman and Smith, 2013) that found periods of glacier expansion at ca. 2470–2410, 1850, 1450, and 830 years BP.
Here we examine satellite imagery from 1986, 1997, 2010 and 2013. The yellow, red, and green arrows indicate the same location in each image. In 1986 as in the map the Bromley Glacier was comprised of three large glacier tributaries, two flowing from the east red and pink arrow and from due south. In 1986 the eastern tributaries still contributed directly to Bromley Glacier. The terminus was at the lime green arrow, 500 meters beyond a side valley on the west marked by the yellow arrow. In 1997 the tributary at the red arrow is no longer feeding the Bromley Glacier while the tributary at the pink arrow connection has narrowed. The terminus has retreated 200 m since 1986, but still rounds the bend heading northeast. In 2010 the separation at the red arrow is greater than 1 kilometer. The pink arrow tributary is also no longer in contact with Bromley Glacier. The terminus has retreated to the yellow arrow, a 700 m retreat since 1986. The lower 500 meters of the glacier are narrow and thin. By 2013 the glacier has retreated to the dark green arrow, an additional 500 m since 2010 and 1200 m since 1986. The red tributary has retreated 1400 meters from Bromley Glacier and the pink arrow tributary 250 m from Bromley Glacier.
The loss of contributions from two of the three main tributaries will spur continued extensive retreat of the glacier. The snowline of the main glacier has been at close to 1600 m in the imagery here, too high for anything but a very negative mass balance. This retreat is similar to that of nearby Chickamin Glacier, Porcupine Glacier and Nass Peak Glacier. There is an exceptional photo gallery provided by the Tree Ring Lab at University of Victoria, the album does not get to the Cambria Icefield and Bromley Glacier until image 123, though images 65-68 have excellent examples of fossil trees. Figure 2 from Hoffman and Smith (2013) is below. This is in the area rendered ice free by the retreat of the red arrow tributary since 1986.
1986 Landsat image
Figure 2 from Hoffman and Smith (2013) of red arrow tributary that was connected to Bromley Glacier in 1986, this is a 2011 image.