Some more kinda wild speculation

While there are sources that state that the 6th calamity was caused by The Elementals who were upset with everyone's misuse of the world's aether, it seem like that info is shaky. So I think we can assume that one of the 5AA super powers, more likely Amdapor developed magicks or a weapon which aspected to water as The Tenth was drowned out that caused the flood. Like how Mhach started augmented their power with The Void, I think Amdapor would utilize another plain of existence: The Aetherial Sea, and their first, and only use of a weaponized Life Stream caused the calamity. And this power is locked away in the Occult Crescent.