The several dozen mountain glaciers in southern New Zealand are only 20° north of the Antarctic ice sheet but they present a remarkable contrast. Under the strong marine influence glaciers like the Tasman get an annual accumulation of new snow measured in some places as much as 4 to 6 meters and probably as much as 10m per yr above the 2100-m level in the passes of the Southern Alps. This is intermediate between heavy west coast and lighter east slope precipitation; it agrees well with mean annual precipitation of 400 cm at The Hermitage near the end of Tasman Glacier. The accumulation limit is near 1800 m, and even here 2 to 4 m of snow collects and then melts each year. New snows generally have densities of 0.20±0.05, but one-year-old urn is coarse and hard (0.62±0.05) because of soaking and sublimation while two-year-old accumulation is nearly ice (0.72) with many ice crusts.
To feed upper Tasman Glacier this broad deep accumulation funnels its ice into a spectacular long valley averaging only 1.2 km wide. Surface speeds of 40 to 60 cm per day have been common over three years with some diminution at the edges. Summer velocity is 20 pct faster than winter. Twelve kilometers down Tasman Glacier from the firn limit the motion decreases rapidly; another 12 km of lowest glacier is protected by an ablation moraine 1 to 2 m thick. Instead of retreating since photos of the early 1900's, this whole lower glacier has thinned 60 m and gathered its dirt cover.
Ablation is as spectacular as accumulation and motion. Under marine influence summer days near the glacier toe (760 m) vary between 8 and 18°C and midwinter days are only −4 to +5°C. Meit rates on white ice halfway up to firn limit average 10 cm per day over short periods, and the snow-free melt season here exceeds 200 days. Total measured ablation gives ice losses up to 1338 cm per year; they vary strictly with altitude (about 1000 at 1200 m, 700 at 1400 m, 500 at 1600 m) and the meteorological character of the season. The first rough figures indicate that the 1958–59 budget year was negative with 1.13×10⁸ m⁸ water equivalent of ice loss.