Sedimentological investigations in the forefield of an Icelandic surge-type glacier: implications for the surge mechanism

A sedimentological study in the forefield of Hagafellsjokull Vestari, Iceland has been employed to distinguish between pervasive sediment deformation and sliding as mechanisms of basal motion in surge. Ice retreat following a surge in 1979/80 has exposed a two-layered quasi-continuous till cover and a suite of streamlined bedforms, including flutes and drumlins. An integrated approach using particle size data, clast morphology, scanning electron microscopy and micromorphology suggests that comminution processes were confined to the uppermost 16-25 cm of the till. The lower till layer remained relatively undisturbed during the surge advance in both drumlinised and non-drumlinised areas. Micromorphological evidence of a clay depositing ice-sediment water layer suggests that decoupling was important during the surge phase. We suggest that the till did not weaken sufficiently for pervasive deformation to occur at depth. Rather the surge mechanism at Hagafellsjokull Vestari is thought to involve the transition of the quiescent phase basal water system, which consists of a few large subglacial conduits emerging at the ice margin, to a distributed or linked cavity system. (C) 2002 Elsevier Science Ltd. All rights reserved.