Legend of Korra

Earth is lava at 700-1200 C. That's a lot of energy to produce (manipulate? convert?).

Considering there's plenty people in the series like the factory workers who can generate lightning (which is several times hotter than the sun), producing enough energy to melt some rocks isn't that unfeasible. Between water benders being able to control steam and sand benders existing, I'm surprised we haven't seen a lava bender sooner.

That said, their group makes me wonder if Zaheer will do something unique like making vacuums.