Miss ice formation of enormous proportions (7)
I believe the answer is:
seismic
'of enormous proportions' is the definition.
(I've seen this before)
'miss ice formation' is the wordplay.
'formation' indicates anagramming the letters.
'miss'+'ice'='missice'
'missice' anagrammed gives 'SEISMIC'.
(Other definitions for seismic that I've seen before include "Earthshaking" , "Caused by an earthquake" , "shock" , "like tremors?" , "Of earth tremors" .)