Validate changes coming about with tsunami (5,4)

I believe the answer is:

tidal wave

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'tsunami' is the definition.
(synonyms)

I can't explain the rest of the clue.

(Other definitions for tidal wave that I've seen before include "Large movement (of water or public opinion)" , "potential disaster, naturally" , "Huge movement of public opinion" , "Overwhelming surge" , "Huge sea surge" .)

I've seen this clue in The Sun.

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