Glaciers and Snow Cover

The text in this section has in part been adapted from:
Fitzharris, B., Lawson, W., and  Owens, I., 1999. Research on glaciers and snow in New Zealand. Progress in Physical Geography, 23 (4). 469–500.

New Zealand’s glaciers and snowfields are the most significant in the Southern Hemisphere, outside Antarctica and the Andes. However, only a few New Zealand glaciers have any sort of a constrained history. There are more than 3100 glaciers in New Zealand that exceed 0.01 km2 in area, and together these comprise a total of 53.3 km3 of ice volume (Chinn, 1989a). The bulk of this ice is located in the icefields of the Mt Cook (3748 m) area of the Southern Alps. New Zealand’s largest glacier is the Tasman Glacier (29 km long), which flows north–south along the eastern flanks of Mt Cook. The well-known and accessible Fox and Franz Josef Glaciers flow westwards from the slopes of Mt Cook down steep-sided valleys to ~ 300 m a.s.l.

Seasonal snow extent across the Southern Alps is determined by the winter altitude of the snow-line. This is highly variable, but averages ~1000 m. In early spring, snow usually covers about 55 000 km2, or 35% of the area of the South Island. Seasonal snow accumulation exceeds 4000 mm water equivalent near the Main Divide of the Southern Alps. Total volume is estimated at about 30 km3 (Chinn, 1969; Fitzharris, 1979). By the end of summer the snow-line retreats to altitudes of between 1500 m in the west and 2200 m in the northeast of the Southern Alps (Chinn and Whitehouse, 1980). This snow and ice is produced by New Zealand’s humid maritime climate and the orientation of the main Southern Alps range across the dominant Southern Hemisphere westerlies (Fitzharris et al., 1992b). Precipitation rates reach 12 000 mm a–1 a few kilometres west of Main Divide, but there is a strong east–west precipitation gradient so that they fall to 1000 mm a–1 or less to the east (Griffiths and McSaveney, 1983). Precipitation is evenly distributed throughout the year so that at high altitudes substantial amounts of snow can be deposited even in summer. However, the midlatitude, maritime location and high summer solar radiation levels also mean that there is much melt. Consequently many glaciers and snow areas have a high input–output of mass, or high ‘activity index’ (Meier, 1961).

The Southern Alps are very sensitive to climate change and provide a relatively ‘clean’ climatic signal. The maritime glaciers of New Zealand form the wet, warm, maritime end of the glacier response scale with dry, cold continental glaciers being at the opposite end. Thus the study of processes and modelling of New Zealand glaciers is of inherent scientific interest.

The glaciers and snow cover of the Southern Alps provide a resource for hydroelectric generation, agriculture and horticulture based on irrigation, the ski industry and tourism. Snow also contributes to hazards such as floods and avalanches, and its distribution has critical ecological implications for many protected natural areas, such as National Parks, the majority of which are located in the mountains.