Land due to turbulence? That’s knotty (9)

I believe the answer is:

nodulated

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'knotty' is the definition.
(thesaurus)

'land due to turbulence?' is the wordplay.
'land due to' can be anagrammed to 'NODULATED'.
Though, I'm not clear how the anagram is indicated.

'that's' is the link.

Can you help me to learn more?

(Another definition for nodulated that I've seen is " Having abnormal growths".)

I've seen this clue in The Times.

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