The questions this photo begs are--what is at the bottom of that hole, and how far down below the "blackness" does it go???
It almost looks like there's this thick crust that the city is built on, with literally NOTHING beneath it for quite some distance. Almost like the top layer of a lake froze over, and then they drained the water out from beneath the ice, just leaving the ice crust on top. If everyone jumped simultaneously, the whole city could crack through the crust and fall in.