(Lava Cavern isn't a spell.)
When Lava Cavern enters the battlefield, return a land you control to its owner's hand.
Sacrifice a land: You gain 1 life.
: Add or to your mana pool.
Put Lava Cavern on top of your library: Add to your mana pool.
: Add 
or 
to your mana pool.
to your mana pool. 
