Sea creature in major catastrophe (4)
I believe the answer is:
orca
'sea creature' is the definition.
(term for a killer whale)
'in major catastrophe' is the wordplay.
'in' says the answer is hidden in the clue.
'ORCA' is hidden within 'major catastrophe'.
(Other definitions for orca that I've seen before include "Killer in deep" , "Predatory black and white toothed whale" , "School killer" , "Large predator" , "Killer at sea" .)