Forget the middle paragraph of my last post, I saw this thread before i saw the lava world thread and the lava world thread answered all of the questions in the middle paragraph.
Obsidian is available when lava cools down, the lava itself is not a resource now. its there to make buulding base more difficult as it moves and increases. You can stop the flow by building paste paths, but when an eruption happens you have to move fast to catch the resources. The lava spreads fast and makes acces to the resources impossible if you're not on time.