Rising temperatures are moving increasing amounts of meltwater through Greenland’s ice sheets. This has a direct impact on how the ice behaves over both the short and long term.
Scientists have held that meltwater flowing beneath the ice sheet is the primary factor that determines how strongly the ice sticks to the earth below. This in turn sets how fast an ice sheet flows. Now, a new look the subject suggests the flow could be much more complicated.
Ryser et al. present measurements of ice deformation and water pressure beneath the glacier as well as surface ice velocity. By planting sensors at various depths throughout the ice column, the researchers retrieved unique data that show how the ice sheet moves in a caterpillar-like manner, extending and compressing with differing surface velocities and deformation patterns.
The researchers used two test sites close to the ice sheet margin. There, they found that movement at the base of the ice sheet was responsible for 40 to 70 percent of the motion on the surface during winter and caused as much as 90 percent of the motion in summer, when activity speeds up. Their models show that shifting stress between slippery and sticky bed patches beneath the ice proved to be a crucial factor in determining the speed. Until recently, it was unclear exactly how surface speeds were set by ice melt and movement at the base of the ice sheet. In the past, ice sheet studies had to use untested assumptions.
The team’s find of a caterpillar-like flow in the ice sheet sets the stage for future fieldwork and modeling using refined data from elsewhere in Greenland. (Journal of Geophysical Research: Earth Surface, doi:10.1002/2013JF003067, 2014)
—Eric O. Betz, Freelance Writer
Citation: Betz, E. O. (2015), Caterpillar-like motion of the Greenland ice sheet, Eos, 96, doi:10.1029/2015EO023803. Published on 11 February 2015.