You know you're a law professor when you look at a story like this and think, “I bet that would make a great Torts final exam question.”
And I don't even teach Torts. (Actually, there's probably some way to make it a Property final exam question too, if you do easements…)
Aside from the ingress / egress easement implied at (American) law, there’s going to be a lateral and subjacent support issue coming up soon…
An interesting example for the property rights absolutists. If nobody can tell me what to do with my own property, they also can’t tell my neighbors not to dig a really deep hole.