[quote=Gowi]
Right, I was thinking about the Pre-Roku Avatar, though I could've sworn Sozin had some control over it but I'll have to rewatch Series 1 to see why I'm remembering it like that. But yeah, the problem I had with Ghazan's lavabending (which was more magmabending if you ask me) was how does an Earthbender heat up Earth to turn it into that? What are the fundamental mechanics behind it? Earthbenders don't deal with temperature but mineral content. Again I think it was poor hindsight on the writers part with them making characters powerful enough to fight the Avatar (and win) but without explanation of their ability.
[/quote]

Waterbenders can turn water into ice or heat it up into steam. There's no reason earthbenders shouldn't be able to do the same to their respective element. The fundamental mechanics behind it are [i]magic[/i], because that's what it is.