if you watched the Cinematic Intro Movie to the game you'll notice those waterfalls are where they fought the Morbol, and below where the Garlean Warship + Dragons were fighting. The Warship + (Dragon/Bahamut) fell into the area and released a bunch of Aetheryte + Primals. That area is now Mor Dhona. Waterfalls are now Mor Dhona.