WordNet sense 1 (start to burn or burst into flames):

ignite, combust, conflagrate, catch fire, take fire

WordNet sense 2 (force out or release suddenly and often violently something pent up):

break, burst

WordNet sense 3 (break out):

break through, come out, push through

WordNet sense 4 (start abruptly):

break out

WordNet sense 5 (become raw or open):

recrudesce

WordNet sense 6 (erupt or intensify suddenly):

flare, irrupt, break open, burst out, flare up

WordNet sense 7 (become active and spew forth lava and rocks):

belch, extravasate