WordNet (r) 3.0 (2006):

flare up
    v 1: ignite quickly and suddenly, especially after having died
         down; "the fire flared up and died down once again"
    2: erupt or intensify suddenly; "Unrest erupted in the country";
       "Tempers flared at the meeting"; "The crowd irrupted into a
       burst of patriotism" [syn: erupt, irrupt, flare up,
       flare, break open, burst out]

Moby Thesaurus II by Grady Ward, 1.0:

123 Moby Thesaurus words for "flare up":
   access, bake, be angry, be excitable, be in heat, belch, bellow,
   blaze, blaze of temper, blaze up, bloom, blow a gasket, blow up,
   blowup, bob up, boil, boil over, break forth, bristle, broil, burn,
   burst, burst forth, cascade, catch fire, catch the infection,
   choke, combust, come apart, convulsion, cook, cyclone, debouch,
   debouchment, deflagration, dissiliency, eructation, erupt,
   eruption, excite easily, explode, explosion, fire up, fit, flame,
   flame up, flare, flash, flash fire, flash up, flicker, flip, flush,
   fry, fume, gale, gasp, get excited, gleam, glow, go into hysterics,
   gush, gust, have a tantrum, high words, hit the ceiling, hurricane,
   ignite, incandesce, irrupt, irruption, jet, kindle, outbreak,
   outburst, pant, parch, paroxysm, pop up, radiate heat, rage, ramp,
   rant, rant and rave, rapids, rave, roast, run a temperature, rush,
   sally, scald, scene, scorch, seethe, seizure, shimmer with heat,
   simmer, smolder, smother, spark, spasm, spate, spew, spring up,
   spunk up, spurt, start up, steam, stew, stifle, storm, suffocate,
   sweat, swelter, take fire, tempest, toast, tornado, torrent,
   turn a hair, upheaval, volcan, whirlwind