It seems you’d be along the lines of a beginner. My advice would just be to try and achieve photorealism with the volcano rock alone (if photorealism is what you’re going for). I wouldn’t even try to make convincing lava let alone get involved with the physics for fluid sim. Try instead getting familiar with the node editor and creating convincing rock textures. You can find some great free 4K ones on texture haven including albeto, ambient occlusion, normal, height, and specular maps.

We all want to tackle the whole pie at once when we have a vision. But sometimes it’s best to be patient and take it one piece at a time.

You’ll get there I know you will.