Nuclear. I think in Australia, the humans blew up the factory by attacking the reactor. It's left that area irradiated.

[ Hmm, she's a little curious about that noise and wonders why he's awake too. It's not like they're all having bad dreams, right? Right? ]

Oh, that's fascinating! I'll have to talk with some of the Ingress technicians to see if they can tell me more about it.