Lava is the fuel for your spells. You start each turn by refilling your available lava, and the amount you have access to goes up with every passing turn, allowing for bigger and bigger plays as the game progresses.
Player 1 starts on 1 Lava, and Player 2 starts on 2, to offset the advantage from going first. Lava then increases by 1 point each turn up to a maximum of 10.
Lava is not carried over from one turn to the next; anything you don’t use is wasted, and your total refills at the beginning of each turn. You cannot hold more than 10 lava at one time.