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This is a photograph of Muir Glacier in Alaska taken on August 13, 1941, by glaciologist William O. Field. This is a photograph taken from the same vantage point on August 31, 2004, by geologist Bruce F. Molnia of the United States Geological Survey (USGS). According to Molnia, between 1941 and 2004 the glacier retreated more than twelve kilometers (seven miles) and thinned by more than 800 meters (875 yards). [...]