Some mount eruption can be earth-shaking (9)
I believe the answer is:
momentous
'earth-shaking' is the definition.
Both the definition and answer are adjectives. Perhaps there's an association between them I don't understand?
'some mount eruption can' is the wordplay.
'some mount' can be anagrammed to 'MOMENTOUS'.
But, I'm unsure how the anagram is indicated.
'be' is the link.
Can you help me to learn more?
(Other definitions for momentous that I've seen before include "major" , "of great significance" .)