Freak Breaches appear as freaks attempt to escape from the destroyed lairs to the surface so they can attempt to get to safer hideouts. They are required for 2 achievements, one is for closing a single freak breach, the other is for closing all freak breaches in the game, freak breaches do not contain titans, which is a relief, but if there are leaper mutants you will have a time chasing them across the rooftops as they attempt to escape & survive what you did to their hive