burst out vs flare up

burst out and flare up both are verbs.

Word	Noun	Adjective	Verb	Adverb
burst out	No	No	Yes	No
flare up	No	No	Yes	No

As verbs, burst out and flare up are synonyms defined as:

Other synonyms of burst out include break open, erupt, flare, irrupt.

burst out (verb)	flare up (verb)
erupt or intensify suddenly	erupt or intensify suddenly
give sudden release to an expression	ignite quickly and suddenly, especially after having died down
appear suddenly or unexpectedly; happen unexpectedly