November 23, 2010
Banded Glacier a new alpine lake
Posted by Mauri Pelto
Banded Glacier comparison in 1998 (left) and 2011 (right) Google Earth images. Red arrows and dots indicate 1998 terminus-margin. Yellow arrow and dots indicate 2011 terminus-margin
The Banded Glacier on Mount Logan in the North Cascades of Washington has retreated since 1950 creating a new alpine lake, that is not evident on USGS maps of the time. In 1960 the glacier was 450 m wide ending in a lake that was 100 m across,1960 image from Austin Post (USGS). Banded Glacier had an area of 0.8 square kilometers in the 1958 based USGS map. From 1960 to 1998 the glacier retreated 300 m. From 1998 to 2011 the glacier lost 35% of its area declining from 0.47 square kilometers to 0.30 square kilometers, 62% loss in sixty years. In 2015 an image from Sean O’Rourke illustrates that the glacier has retreated from the proglacial lake that it had ended in the previous 60 years. Note the spread of rock outcrops in the accumulation zone suggesting this glacier will have trouble surviving. The north side (left side in the image) is very short at this point. The number of crevasses has also diminished as the glacier has thinned, become shorter and as a result moves slower. The slower movement indicated by the reduced calving is despite an increase in surface slope as the glacier has retreated from the flatter lake basin area onto the slopes leading to the summit of Mount Logan. The retreat from 1998-2015 is 280 meters.This glacier is difficult to view unless you are right in the basin where it is. In 2003, 2004, 2005, 2009, 2014 and 2015 this glacier lost almost all of its snowcover, a sign that the glacier cannot survive (Pelto, 2010). The image below is from late June 2015, a time when typically no blue ice would be showing, instead 25% of the glacier has already lost snowcover. This glacier is retreating as are all North Cascade glaciers, with 2015 being the worst year for the mass balance of glaciers in the last half century (Pelto, 2015).
1960 image at left from Austin Post (USGS) at right Banded Glacier image from Sean O’Rourke (c) used with permission.