Increase in destruction of a coastline (10)
I believe the answer is:
escalation
'increase' is the definition.
(I know that escalation is a type of increase)
'destruction of a coastline' is the wordplay.
'destruction of' indicates an anagram.
'a'+'coastline'='acoastline'
'acoastline' anagrammed gives 'ESCALATION'.
'in' is the link.
(Other definitions for escalation that I've seen before include "Rapid growth" , "sudden rise" , "expansion" , "Rapid rise in level" .)