WordNet sense 1 (liable to lead to sudden change or violence):

explosive

WordNet sense 2 (lacking stability or fixity or firmness):

unstable

WordNet sense 3 (marked by erratic changeableness in affections or attachments):

fickle

WordNet sense 4 (likely to change frequently often without apparent or cogent reason; variable):

inconstant

WordNet sense 5 (such that alteration is possible; having a marked tendency to change):

changeful