Any good theories about The Doom?

I have one, but it's a little outlandish. What if the Valyrians were an even more technologically advanced civilization, comparable to our own modern society? And what if The Doom was some kind of nuclear fallout?

This would explain the immense heat that supposedly incinerated even dragons, and also why no one can go to Valyria without dying (of nuclear radiation). I'm fascinated by the idea of a fantasy world where there once existed advanced technology, but an apocalyptic event sent them back into the Dark Ages.

By the way, I've only read about 700 pages of ADWD, so if there's some sort of revelation about Valyria or The Doom that's still to come, I'd rather not be spoiled.