SUBGLACIAL OBSERVATIONS FROM OKSFJORDJOKELEN, NORTH NORWAY

Stepped bedrock topography at the snout of a small outlet glacier from Oksfjordjokelen, North Norway, produces an extensive subglacial cavity system which stretches some 70 m across and 100 m up-glacier, giving access beneath ice less than or equal to 50 m thick. Inside the cavity, regelation ice, clean glacier ice and deforming basal ice have been observed. Samples were taken and basal debris concentrations at the glacier sole were found to vary between 0.005 and 15.38 per cent by volume. The basal ice velocity has been determined using a linear variable differential transformer attached to an analogue recorder, and also by means of measured displacements of ice crews and clasts embedded in the basal ice. Velocities were found to differ both spatially and temporally from a maximum of 2.55 mm h(1) to a minimum of 0.3 mm h(-1). The measurements and observations, which have been related to present theory, show how spatially averaged values for a number of variables could lead to inaccuracies in predicted erosion values, certainly at a local scale. On the exposed foreland, joint-controlled lee-side faces provide evidence for extensive subglacial plucking (here taken to mean the removal of pre-loosened bed material and/or material resulting from bed failure). Indeed, in the cavity the early stages of removal of joint-controlled blocks by ice deformation along joints have been observed. The importance of debris-rich basal ice is shown in the formation of large striations (up to 500 cm x 16 cm x 2 cm) present on the foreland.