Bottom sliding of a glacier measured from the surface

Abstract

WE have measured the sliding motion at the bottom of a glacier from the surface of the ice. Fleming Glacier in the Antarctic Peninsula is a fast flowing polar glacier, more than 1,000m thick, feeding the Wordie Ice Shelf. Observations indicate that up to a third of its surface velocity is due to the bottom layers of ice sliding over the bed. Previous measurements of the bottom sliding of glaciers have been confined to tunnels or boreholes that have reached bedrock1,2; sliding velocities have also been calculated indirectly by using assumptions about the internal deformation of ice3. Results obtained by our method can help to test theories of basal sliding4 and should give insight into the mechanism and consequences of surges in glaciers and ice sheets5.