What happens when your land disappears due to natural disaster?

If your land erodes away into a river or is covered by a volcano or falls of a cliff, what do you get? insurance could pay to rebuild your home, but on what? the land is gone. would you still have to own the property that doesn't exist because you can't sell it? would you have to pay taxes on the nonexistent land? this question came up when watching the weather channel and they showed houses just falling into raging storm waters.