Columbia Glacier, one of Alaska's best-known, most-viewed and fastest-changing glaciers, has retreated so far back that it is now separated into two sections, a transformation captured by satellite imagery.
NASA's Earth Observatory has compiled a time-lapse series of images that shows changes to Columbia Glacier between 1986 and now, a period of rapid retreat.
Since the 1980s, Columbia Glacier has lost about half of its thickness, according to NASA. Between then and now, there were years with particularly rapid shedding of ice chunks, creating a "mélange" of floating icebergs that rafted together, as the NASA time-lapse images show. One of those years was 1989, when the ill-fated Exxon Valdez supertanker diverted course while carrying its load of oil from the Valdez terminal of the trans-Alaska oil pipeline. At the time, the need to avoid floating glacier ice was cited as the reason for the course diversion.
By 2007, melt from Columbia Glacier had already reached 87 percent of the anticipated volume that will contribute to sea-level rise, according to a University of Colorado study published in 2012 in The Cryosphere.
After 2007, the glacier's terminus became detached from the seafloor and was transformed into a floating tongue, changing the pattern of iceberg production, according to a study published in 2010 in the journal Geophysical Research Letters. Instead of shedding its ice though a steady pattern of low-volume bergs calving off the terminus, the glacier began losing mass in larger chunks falling off in episodes, according to the study.
When will Columbia Glacier's retreat stop? The 2012 University of Colorado study used computer modeling to predict that the terminus will retreat until about 2020, when it reaches a new stable position about 15 miles upstream from the previous spot of stability reached in the 1980s. NASA has cited another estimate of 2030 as the time when the glacier will have retreated so far that it is at the shoreline and no longer able to shed ice into Prince William Sound.