Temperature and bathymetry of ice-contact lakes in Mount Cook National Park, New Zealand

Several ice-contact lakes have formed in conjunction with twentieth century glacier retreat in Mt Cook National Park. They occupy overdeepened glacial valleys and are damned by terminal moraines and/or outwash heads. During the autumns of 1994 and 1995, the temperature and bathymetry of "Maud lake", "Godley lake", and Hooker Lake were surveyed. The near-glacier vertical water temperature profiles exhibited greater temperature variation than those at the distal ends of the lakes. Thermal stratification existed in Hooker Lake, whereas both Maud and Godley lakes were thoroughly mixed. Water temperatures in the latter were consistently between 3 and 4.5 degrees C, but most parts of Hooker Lake were cooler than 2 degrees C, with a minimum recorded temperature of 0.2 degrees C. These contrasts are important because melting of submerged parts of glacier termini is significant for ablation rates and for the dynamics of calving termini. All the lakes are steep sided and deep. Maud and Godley lakes approach 100 m in depth, whereas Booker Lake has a maximum recorded depth of 136 m. Extensive flat floors in Maud and Godley lakes probably reflect rapid sediment accumulation following glacier retreat. Water depth at the termini of iceberg-calving glaciers is known to correlate strongly with rates of iceberg production and hence the rate of glacier retreat. However, given the substantial water depths through which these glaciers (and also the neighbouring Tasman Glacier) have retreated, they appear to be more stable than comparable glaciers in other countries. The subaqueous geometry of all the glacier termini comprises a projecting ramp of glacier ice. All the lakes are being enlarged by glacier retreat except Maud lake, which has been reduced in size since 1995 by the advance of Maud and Grey Glaciers.