Eastern Island in sound crumbles (6)
I believe the answer is:
erodes
'crumbles' is the definition.
The definition and answer can be both related to change as well as being verbs in their -s form.
Maybe you can see an association between them that I don't see?
'eastern island in sound' is the wordplay.
'eastern' becomes 'e'.
'island in sound' becomes 'rodes' (I can't explain this - if you can you should give a lot more credence to this answer).
'e'+'rodes'='ERODES'
Can you help me to learn more?
(Other definitions for erodes that I've seen before include "Wears away with weather" , "Eats away" , "Wears away as by time or water" .)