"vulnerable to bergschrunds ... and avalanches from overhanging seracs."

Amundsen describes the sides of Nansen as follows:

Ice blocks and sinister piles of snow told their tale of avalanches constantly tumbling from the mountains on the flanks.

Over by Fridtjof Nansen we could not go; this mountain rose perpendicularly, in parts quite bare, and formed with the glacier a surface so wild and cut up that all thoughts of crossing the ice-field in that direction had to be instantly abandoned.