It's specified that even being indoors or in a cave won't save you from the effects. The only thing that kept a few people safe was Sasuke's Rinnegan-powered Susano'o.
I imagine that if it permeates through caves and such, it would also work along the curves of the planet. The other aspect is that it grows a tree that pulls everybody into its roots/branches.
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(He/Him) I write Naruto Fanfiction. But I am definitely not a furry.