I noticed that when Dragons crash, the terrain they land on deforms. Is this just an object that's created, or is it possible to change Skyrim's terrain mid-game?

I believe it's just an object created on the ground.

Oh, that's a shame. I got all excited when I noticed that- thought it would have been cool for, like, Tundra Defense or RTS.

I thought it was a really big decal?

Edit: Unless it has collision, than it's probably an object. I think the last time I managed to damage a dragon with arrows in the air enough for it to crash was...ages ago...so I'm not sure.