What changes when the snow melts! (4)

I believe the answer is:

thaw

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'when the snow melts' is the definition.
I can't tell whether this definition defines the answer.

'what changes' is the wordplay.
'changes' indicates anagramming the letters.
'what' anagrammed gives 'THAW'.

Can you help me to learn more?

(Other definitions for thaw that I've seen before include "Melt in heat" , "What - melt like snow?" , "John, once regularly on TV" , "De-ice" , "Player of detective" .)

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