Down-wasting has affected southern glaciers in New Zealand later than northern glaciers under the influence of a southward rising snow line which is attributed to a southerly shift in prevailing wind belts. Evidence from the Hooker Glacier indicates that the present period of wasting is the fourth of a series which began about 200 years ago.
As the firn line rises a glacier is planed in the ablation zone so that successive surfaces are parallel to the original surface, which shows that ablation is more active for a short distance below the fern line than near the terminal face. A period of accelerated terminal retreat can result from parallel down-wasting without a correlative acceleration in the rate of climatic change.