Solution 9 - Unfounded Speculation!

[MikkoAkure]

That reminds me. Do we know the exact location of the Ridorana Lighthouse? Cus if its situated on that chasm that crosses the new world (probably the western tip of it, closer to Hingashi.) then somewhere in the New World might be an origin point for the Garleans. That would definitely not make the chasm recent a development, since the Lighthouse was supposed to be pretty old, I think?

There is a place on the Valnard Sea, far to the south of Rabanastre, where the ocean tumbles into a gaping maw more than a malm across─the Ridorana Cataract. Legend would have us believe that it is the entrance to the Hell of Water. Many a scholar seeking to prove otherwise has descended into the chasm─some even by airship─but not a one has returned.

Ridorana is the name of both a massive gap in the southern Valnard Sea, and the lighthouse once manned by the Royal Dalmascan Navy to prevent ships from succumbing to the cataract's currents.

In the Valnard Sea to the south, a lighthouse perches on the lip of the Ridorana Cataract - a gaping maw in the ocean believed to lead into the seventh hell. This spire illuminates the path to the northern sea routes, and thence to the docks of Valnain.

Far to the south of Rabanastre, in a remote corner of the Valnard Sea

Not exactly descriptive since neither Ridorana nor the Valnard Sea show up labeled on maps, but it's not anywhere near the New World nor Hingashi in any case. All we know is that it's "south of Rabanastre", "far from civilization", yet close enough that Dalmasca was responsible for it and it was abandoned after Garlemald conquered them. It also seems to point trade towards Valnain, which we know the location of. There's also a blink-and-you'll-miss-it sight of coastline in the distance from the lighthouse. It's also close enough that airships can go there. They don't have infinite range after all.

We know that the Ridorana Cataract was created by an explosion at Goug during Ramza's time there and it forced the Gougans/Garleans there to relocate. The ocean hole in Tural seems to originate in the middle of the ocean between Aldenard and Tural and it forks after hitting the continent. It's probably important though and will likely show up in Dawntrail at some point, whether in the the main expansion story or the patches.