High Street art, an assembly that’s cataclysmic (5-10)

I believe the answer is:

earth-shattering

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'cataclysmic' is the definition.
Both the definition and answer are adjectives. Perhaps you can see a link between them that I don't see?

'high street art an assembly' is the wordplay.
'assembly' is an anagram indicator.
'high'+'street'+'art'+'an'='highstreetartan'
'highstreetartan' anagrammed gives 'EARTH-SHATTERING'.

'that's' acts as a link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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