JBJB1029, kindly stop talking about your fanfictions as movies. They are no movies and pretending them to be will just create false rumors.
As for disasters in LBT that we haven't seen yet there would be:
- Drought based on dry weather (rather than one that can be just fixed by breaking a dam.
- Oil or gasfires (not likely in the Great Valley unless there was any spot where oil or gas reached the surface where it might be ignited by lightning strike (there are places on earth where fires caused by this burned for decades or even centuries though locally just at the spot where the oil or gas reached the surface)).
- While there have been several volcanic eruptions in LBT, they never included a pyroclastic flow.
- There also hasn't ever been a Limnic eruption.
- Hail is another thing, but I think you are quite aware of that one.
- We have never had any dealings with poisonous plants (not quite a natural disaster, but interesting enough for stories).
For all we know, the native population of the Valley was already overwhelmed once, in the original movie. And it seems they were peacefully assimilated.
In which case "overwhelemed" wouldn't really be apply. Perhaps immigrants were simply welcome.