April 5, 2013
Porcupine Glacier is a 20 km long outlet glacier of an icefield in the Hoodoo Mountains of Northern British Columbia. 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. Here we examine the retreat of Porcupine Glacier and the expansion of the lake it ends in from 1988-2011 using four Landsat images from 1988, 1999, 2010 and 2011. Below is a Google Earth view of the glacier with arrows indicating the flow paths of the Porcupine Glacier. The second images is a map of the region from 1980 indicates a small marginal lake at the terminus.
In 1988 a tongue of the glacier in the center of the lake reached to within 1.5 km of the far shore of the lake, yellow arrow. All but the red arrows are in the same location in each of the images below. The orange image is at the 1988 terminus position on the northern edge of the glacier, the purple arrow indicates the 1988 terminus position on the south side of the glacier. The yellow arrow indicates the 1988 center tongue position. The pink arrow is the 2011 terminus position at the north edge of the glacier. The glacier has retreated 2 km in the 22 year period. The number of icebergs in the lake at the terminus indicates the retreat is mainly due to calving icebergs. Glacier thinning of the glacier tongue leads to enhanced calving. The glacier tongue has a low slope up to an icefall, noted by red I, at this icefall the glacier rises from 450 m to 750 m. This is a likely point at which the lake basin ends and the glacier retreat can slow. The retreat of this glacier is similar to a number of other glaciers in the area Great Glacier, Chickamin Glacier, Patterson Glacier and Bromley Glacier. The terminus viewed up close in 2005 has numerous weaknesses indicating the calving that was going to happen in the next several years.