doomsday event

noun3

1. •
   An occurrence which causes the end of the universe or which destroys the planet earth; a global cataclysm.

   • The universe will contract and grow hotter until the doomsday event that astronomers have dubbed "the big crunch." — 1995
2. •
   A localized event causing widespread death or destruction within a specific geographical area.

   • An earthquake of as much as 7.3 magnitude . . . is the maximum predicted earthquake in Utah, said Johnson. "We could call that a doomsday event." — 2007
3. •
   (figurative) A disastrous occurrence.

   • Protect them against molestation, but if it happens, don't overact and inflate it into a doomsday event. — 1973