NASA has revealed in a new study that a previously unknown mode of ice loss has been discovered at Rink glacier which is located on Greenland’s west coast. Carol Rasmussen of NASA's Earth Science News Team reports that in the years 2010 and 2012, which were the hottest summers on record, not only caused the snow and ice on Rink glacier to melt faster but also caused the ice stream to “slide through the glacier's interior in a gigantic wave, like a warmed freezer pop sliding out of its plastic casing. The wave persisted for four months, with ice from upstream continuing to move down to replace the missing mass for at least four more months.”
This four month long meltwater pulse is now known as a “solitary wave”. Scientists warn that the discovery has “the potential for sustained ice loss in Greenland as the climate continues to warm, with implications for the future rate of sea level rise.”
This animation shows a solitary wave passing through Rink Glacier, Greenland, in 2012, recorded by the motion of a GPS station (circle with arrow). Darker colors within the flow indicate mass loss, red colors show mass gain. The star marks the center of the wave.Here is a sampling of Carol Rasmussen’s compelling piece for NASA JPL.
Rink is one of Greenland's major outlets to the ocean, draining about 11 billion tons (gigatons) of ice per year in the early 2000s — roughly the weight of 30,000 Empire State Buildings. In the intensely hot summer of 2012, however, it lost an additional 6.7 gigatons of mass in the form of a solitary wave. Previously observed melting processes can't explain that much mass loss.
The wave moved through the flowing glacier during the months of June through September at a speed of about 2.5 miles (4 kilometers) a month for the first three months, increasing to 7.5 miles (12 kilometers) during September. The amount of mass in motion was 1.7 gigatons, plus or minus about half a gigaton, per month. Rink Glacier typically flows at a speed of a mile or two (a few kilometers) a year.
The wave could not have been detected by the usual methods of monitoring Greenland's ice loss, such as measuring the thinning of glaciers with airborne radar. "You could literally be standing there and you would not see any indication of the wave," said JPL scientist Eric Larour, a coauthor of the new paper. "You would not see cracks or other unique surface features."
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"We know for sure that the triggering mechanism was the surface melting of snow and ice, but we do not fully understand the complex array of processes that generate solitary waves," said JPL scientist Surendra Adhikari, who led the study.
During the two summers when solitary waves occurred, the surface snowpack and ice of the huge basin in Greenland's interior behind Rink Glacier held more water than ever before. In 2012, more than 95 percent of the surface snow and ice was melting. Meltwater may create temporary lakes and rivers that quickly drain through the ice and flow to the ocean. "The water upstream probably had to carve new channels to drain," explained coauthor Erik Ivins of JPL. "It was likely to be slow-moving and inefficient." Once the water had formed pathways to the base of the glacier, the wave of intense loss began.
The scientists theorize that previously known processes combined to make the mass move so quickly. The huge volume of water lubricated the base of the glacier, allowing it to move more rapidly, and softened the side margins where the flowing glacier meets rock or stationary ice. These changes allowed the ice to slide downstream so fast that ice farther inland couldn't keep up.
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