When it comes to describing sudden bursts of intense emotion or activity, "flares up" is a common term. However, there are numerous synonyms that can be used to convey the same meaning or serve as a variation of the phrase. Tangible examples include "erupts," "ignites," "explodes," "bursts," "sparks," and "fumes." These words can all indicate a sudden increase in intensity, whether it's a fire that flares up or someone's temper that ignites. Additionally, more abstract synonyms such as "escalates," "enrages," "perturbs," or "provokes" are also available to describe sudden bursts of emotion, whether they are positive or negative. Ultimately, there are many options available when seeking alternatives to "flares up," each with their own distinct connotations.