The world's fastest-flowing glacier, the Jakobshavn of Greenland, is draining the land's ice sheet and hence contributing to rapidly rising sea levels. This has been shown by a time-lapse technique which charts dramatic images, taken at least every six hours over an entire year.
According to a report in New Scientist, Jason Amundson of the University of Alaska Fairbanks and colleagues set up a complete "life monitoring" system around the end of the Jakobshavn glacier in Greenland, at the point where it dumps its ice into a narrow fjord and out to sea, during the summer of 2007.
The system remained in place until May 2008.
Each year, 7 percent of the ice lost from Greenland passes through the fjord. The incredible rate at which it sends ice crashing out to sea doubled to 12 kilometers per year between 1997 and 2003.
This increased sea-level rise by 0.06 millimeters per year - roughly 4 percent of the 20th century rate of sea-level increase.
Three cameras took pictures every 10 minutes from 13 May to 8 June 2007, then every hour for the next month, every six hours over the winter and once more every 10 minutes from 7 to 14 May 2008.
Satellite pictures show that the ice sheet is not homogenous - two huge rivers of ice flow out into the fjord. Stitched together, Amundson's images reveal how this happens.
During the summer, huge chunks of ice broke off from the tip of the ice river about every 75 hours - a process known as calving.
In the winter, the ice river grew out over the water at the top of the fjord, creating an ice tongue several kilometers long.
Amundson's pictures show that calving events stopped until the ice tongue disintegrated in four separate events between mid-April and mid-May 2008.
In total, the team recorded 32 calvings.
At each calving event, the ice sheared through its entire 900-meter thickness and the new icebergs would flip over, drag up sediment from the bottom, and shove off into the fjord pushing floating ice ahead of it at a speedy one to two kilometers per hour.
The ice river normally moves downstream 35 meters per day.
In addition to photographing the events, the team measured seismic waves generated by the break-ups and monitored the movement of the ice using GPS stations posted on the ice.