West and East Twin Glacier Extent Change:  1929 – 2011

West and East Twin glaciers are outlet glaciers of the Juneau Icefield (Fig. 1).  They terminate in Twin Glacier Lake in the Taku River valley, just east of the frequently visited Taku and Hole-in-the-Wall glaciers, and approximately 25 kilometers northeast of Juneau, Alaska.

Figure 1:  Location of West and East Twin glaciers, outlined here in blue.  The background black and white image here is a Landsat satellite image from August 15, 2001 (Landsat TM 2001-08-15, panchromatic band, 15 m resolution).

The image below (Fig. 2) shows the extent and retreat of West and East Twin glaciers from 1929 to 2011.  The 1991 to 2011 extents were mapped from satellite imagery while the 1929 extent is an approximation from this 1929 oblique aerial photograph.  East Twin Glacier has continued to retreat from 2001 to 2011, whereas West Twin Glacier ceased to retreat.

 

Figure 2:  Extents of West and East Twin glaciers in 1929, 1991, 2001, and 2011.  The background black and white image here is a Landsat satellite image from August 15, 2001 (Landsat TM 2001-08-15, panchromatic band, 15 m resolution).

View and explore these Twin Glacier outlines in Google EarthTwin Glacier Extent Change: 1929 – 2011

The table below (Table 1) shows the change in surface area as derived from the extents above.  The glaciers are treated here as one entity.  Rates of retreat increased in the 1990s.

Year Area (km2) Area Change (km2) Area Change (%) Rate (km2/a)
1929 140.73
1991 137.82 -2.91 -2.07 -0.05
2001 136.28 -1.54 -1.12 -0.15
2011 136.1 -0.18 -0.13 -0.02
1929-2011 -4.63 -3.36 -0.06
1991-2011 -1.72 -1.25 -0.09

Table 1:  Extent change data derived from the extents above.

Glacier extents (outlines) were digitized manually with GLIMSView (freely available here) from Landsat satellite imagery (freely available here).

References

Beedle, M. J., 2010, GLIMS glacier database. Boulder, CO: National Snow and Ice Data Center/World Data Center for Glaciology, Digital Media.

Beedle, M. J. and Raup, B., 2008, A GLIMS inventory of the Juneau Icefield, Alaska, IGS International Workshop on World Glacier Inventory, Lanzhou, China, Sept. 20-24, 2008.