October 23, 2011

Borealis Glacier separation and retreat

Posted by Mauri Pelto

The Borealis Glacier in the North Cascades of Washington, descends the north side of Primus Peak. Unfortunately the peak is not in prime condition. The thinning glacier has separated into two ice masses, the lower section has also developed a new lake since 1995. The USGS map for the glacier indicates the upper and lower glacier connected by two ice tongues (top image). This connection has been severed by 1990 in an aerial photograph from the USGS(second image). At this point no lake exists below the lower glacier. . In 2006 the lower section of the glacier has undergone a rapid retreat of 200 meters since 1990 and a new lake has formed (top image below). By 2009 the lake has expanded as the glacier has retreated and additional 40 meters (second image below).. This glacier viewed from the edge of the terminus lake in 2009 illustrates the stagnant nature of the lower glacier. The lake will continue to expand at the expense of the lower glacier. The upper glacier has been retreating slowly.