Witness a glacier's staggering seven-year retreat

Since 2004, glaciologist William Pfeffer has been photographing Alaska's Columbia Glacier. By monitoring where the glacier ends and the waters of Prince William Sound begin, Pfeffer is working to understand how coastal ice sheets contribute to rising ocean levels. Now, by piecing his photographs together, Pfeffer… » 4/27/12 11:45am 4/27/12 11:45am