ABSTRACTA photogrammetric survey of the movement of supraglacial boulders together with field survey of surface markers has revealed the spatial and temporal change in velocity on the debris-mantled tongue of Tasman Glacier, New Zealand. Between 1957 and 1986 a general reduction of glacier velocity is recorded, and towards the terminus the local effects of thermokarst erosion on flow vectors became more influential as the downvalley component of velocity decreased. Onlyca.2% of the debris-covered glacier area had no measurable movement, and mature thermokarst sinkholes formed on ice moving at>24 ma-1. Increases in ice velocity and surface elevation 10 km above the terminus were not recorded 2.5 km above the terminus in 1986. Changes in ice volume have been manifested by changes to ice levels and velocity, not by fluctuations of the terminus. The study shows that extensive supraglacial debris mantles and thermokarst forms can exist on actively-moving ice in alpine regions of high debris supply and ablation, and that shear-zone formation is not necessary to explain debris-mantling of such glaciers.