The swells of Anima behind him were growing stronger for every minute that passed. A mind-boggling amount of Anima underneath him had already been sucked into the titanic monolith, enough that it could have powered the entire surface of Mulia for centuries on end with ease.
Lu'um was in right to have started closing the fissure as soon as she noticed the changes down below. The destructive power that was below was not something that the surface could handle, let alone the seas.
Had they opted to not close the fissure, the consequences would've been apocalyptic. Forget about the creatures in Centlani Deep dying, the entire eastern coast would have been obliterated to kingdom come.