From Global Warming Art
Comparison photos of Muir and Riggs Glaciers in Glacier Bay National Park and Preserve, Alaska. Muir glacier, parts of which were greater than 65 meters thick in 1941, has retreated out of the image in 2004 (towards the upper left). The distance to the visible Riggs glacier in 2004 is ~3 km. During this time, the Muir Glacier retreated more than 20 km (Benson and Field 1995).
The Muir and Riggs glaciers are part of the Glacier Bay ice field. In the 1700s, during the little ice age, most of the regional glaciers were merged into a single ice mass that extended ~110 km south of Muir's present location into the Icy Strait of Cross Sound. By 1890, the ice tongue for which Muir was the largest component had already retreated 60 km north (Hall et al. 1995). Tidewater glaciers, i.e. those terminating in channels open to the ocean but sufficiently thick to avoid floating, tend to be unstable when pushed into retreat. If thinned sufficiently, they will start to float off the bottom of the channel and allow sea water infiltration underneath the glacier, which can trigger rapid and prolonged retreat until the glacier reaches a position that is again stable (e.g. Vieli et al. 2002). Because Muir glacier and many other glaciers in the Glacier Bay complex are tidewater glaciers, it is not known how much of the present retreat is a response to recent warming, and how much is the consequence of unstable conditions created by previous warming that has not yet resolved itself (Hall et al. 1995).
- August 13th, 1941 by William O. Field, National Snow and Ice Data Center, may be used freely if properly cited 
- August 31, 2004 by Bruce F. Molnia, USGS, public domain 
This composition was prepared by Robert A. Rohde from the two sources noted above. The composition itself is released under the Global Warming Art license.
- Hall, Dorothy K., Carl S. Benson and William O. Field (1995). "Changes of Glaciers in Glacier Bay Alaska, Using Ground and Satellite Measurements". Physical Geography 16 (1): 27-41.
- [abstract] Vieli, Andreas, Jacek Jania, and Lezek Kolondra (2002). "The retreat of a tidewater glacier: observations and model calculations on Hansbreen, Spitsbergen". Journal of Glaciology 48 (163): 592-600.
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|current||04:07, 25 June 2006||1,000×1,179 (274 KB)||Robert A. Rohde||(fix title)|
|01:16, 25 June 2006||1,000×1,179 (274 KB)||Robert A. Rohde|
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|Date and time of data generation||18:39, 15 October 2004|
|Horizontal resolution||300 dpi|
|Vertical resolution||300 dpi|
|Software used||Roxio PhotoSuite|
|File change date and time||18:39, 15 October 2004|
|Y and C positioning||1|
|Meaning of each component||1230|
|Image compression mode||1.1|