Vehicle is dumped in valley - wreck (9)
I believe the answer is:
vandalise
'wreck' is the definition.
('wreck'->'vandalize' is in my internal thesaurus and 'ize'->'ise')
'vehicle is dumped in valley' is the wordplay.
'vehicle' becomes 'van' (van is a kind of vehicle).
'dumped in' is an insertion indicator.
'valley' becomes 'dale' (dale is a kind of valley).
'is' put within 'dale' is 'dalise'.
'van'+'dalise'='VANDALISE'
(Other definitions for vandalise that I've seen before include "trash" , "Deliberately damage" , "Destroy" , "Wilfully damage" , "Inflict malicious damage" .)