Characteristics and evolution of supraglacial ponds on debris-covered Tasman Glacier, New Zealand

Supraglacial ponds on Tasman Glacier, New Zealand, initiated the development of the large Tasman Lake during the 1980s and still play an important role for ice loss and further terminus disintegration. Limnological and glaciological measurements between 2001 and 2003 reveal distinct differences between ponds. The hydraulic connection of a pond to the englacial water level exerts a key control on whether the pond contributes to longer-term terminus disintegration. In the earlier stages of pond development, ice loss occurs predominantly in the horizontal dimension by subaerial melt. Subaqueous calving at later stages plays a major role for ice loss. During the capture of a pond by the lake, substantial limnological changes lead to changes in relative significance and rates of ice loss processes, the most important being the change from melting to predominantly calving. As a result, ice loss accelerated from around 11 m a(-1) of melt under partial debris cover to a retreat by calving and melting of 34 m a(-1). Ice loss at the ponds accounted for only 10% of the surface loss in the lower terminus area, but is likely to increase in the future with enlargement and coalescence of ponds.