"The entire range disappeared from view as we flew into each trough"

Amundsen’s diary records similar huge undulations in the sea-ice:

On the following day the character of the land began to change; great wave like formations seemed to roll higher and higher as they approached the land, and in one of these troughs we found the land greatly disturbed….. the undulation rose to such a height that it concealed a great part of the land from us.