"the crest of the glacier the terrain started to harden into windblown waves"

Amundsen also reports that:

The going changed at once up here; the loose snow disappeared, and a few wind-waves began to show themselves. These were specially unpleasant to deal with on this last ridge; they lay from south-east to north-west, and were as hard as flints and as sharp as knives. A fall among them would have had very serious consequences.