Morphological and ice-dynamical changes on the Tasman Glacier, New Zealand, 1990-2007

This paper presents data concerning recent (1990-2007) surface morphological and ice-dynamical changes on the Tasman Glacier, New Zealand. We use remote-sensing data to derive rates of lake growth, glacier velocities and rates of glacier surface lowering. Between 1990 and 2007, the glacier terminus receded similar to 3.5 km and a large ice-contact proglacial lake developed behind the outwash head. By 2007 the lake area was similar to 6 km(2) and had replaced the majority of the lowermost 4 km of the glacier tongue. There is evidence that lake growth is proceeding at increasing rates - the lake area doubled between 2000 and 2007 alone. Measured horizontal glacier velocities decline from 150 m a(-1) in the upper glacier catchment to almost zero at the glacier terminus and there is a consequent down-glacier increase in surface debris cover. Surface debris mapping shows that a large catastrophic rockfall onto the glacier surface in 1991 is still evident as a series of arcuate debris ridges below the Hochstetter icefall. Calculated glacier surface lowering is most clearly pronounced around the terminal area of the glacier tongue, with down-wasting rates of 4.2 +/- 1.4 m a(-1) in areas adjacent to the lateral moraine ridges outside of the current lake extent. Surface lowering rates of approximately 1.9 +/- 1.4 m a(-1) are common in the upper areas of the glacier. Calculations of future lake expansion are dependent on accurate bathymetric and bed topography surveys, but published data indicate that a further 8-10 km of the glacier is susceptible to calving and further lake development in the future. (C) 2009 Elsevier B.V. All rights reserved.