Sediment deformation and basal dynamics beneath a glacier surge front: Bakaninbreen, Svalbard

Abstract

Bakaninbreen is a 17 km long surge-type glacier in southern Spitsbergen, Svalbard, which began surging between the springs of 1985 and 1986, forming a surge front where fast-moving surge ice meets non-surging ice. This surge front has propagated 6 km down-glacier over the period to 1995. Instruments known as "ploughmeters" were installed into the deformable sedimentary bed close to the surge front to assess mechanical conditions year-round. Forces experienced by ploughmeters located down-glacier of the surge front are generally lower than those recorded by a ploughmeter up-glacier of the surge front. Ploughmeters installed at the bed down-glacier of the surge front show initially low applied forces, followed by increasing applied forces. We interpret this increase in applied forcing as a late-active-phase motion event. Analysis of ploughmeter data allows calculation of the yield strength of basal sediments. Yield-strength estimates at Bakaninbreen are in the range 16.6-87.5 kPa. Comparison with estimates of basal shear stress suggests that sediments up-glacier of the surge front will be actively deforming, whereas there will be only limited deformation down-glacier of the surge front. Immediately down-glacier of the surge front, calculations indicate negligible basal shear stresses. Together with the deformation of sediment from up-glacier, this implies a build-up of sediment at the surge front, offering a potential explanation for the sediment-filled thrust faults outcropping on the surge front.