Decorate flag with glacial scene (7)
I believe the answer is:
icefall
'glacial scene' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'decorate flag' is the wordplay.
'decorate' becomes 'ice' (to ice a cake is to decorate it).
'flag' becomes 'fall' (I can't explain this - if you can you should believe this answer much more).
'ice'+'fall'='ICEFALL'
'with' is the link.
Can you help me to learn more?
(Other definitions for icefall that I've seen before include "Avalanche; steep part of glacier" , "Steep part of a glacier where the surface is badly broken" .)