Is it possible to build on a volcano?
No, this is not Black & White.
no you can not build a volcano. A Volcano is a natural formation resulting from magma escaping for under the crust. We have no way in game to create such fissures.
Now, if they added recipes for papier mache, vinegar, and baking soda…
I’m not certain. The developer’s stream that featured the volcano, one thought it was possible to build, the other didn’t. It may be possible, but in very limited locations. And god help you if you build on the obsidian. Or in the poison gas area.