erupt vs burst out

erupt and burst out both are verbs.

Word	Noun	Adjective	Verb	Adverb
erupt	No	No	Yes	No
burst out	No	No	Yes	No

As verbs, erupt and burst out are synonyms defined as:

Other synonyms of erupt include break open, flare, flare up, irrupt.

erupt (verb)	burst out (verb)
become active and spew forth lava and rocks	erupt or intensify suddenly
start abruptly	give sudden release to an expression
erupt or intensify suddenly	appear suddenly or unexpectedly; happen unexpectedly
become raw or open
break out
appear on the skin
force out or release suddenly and often violently something pent up
start to burn or burst into flames