The character dialog before a level often has clues as to how to solve the puzzle ahead.
Lava Rivers is a good example: perhaps the lanterns can help us.... we have fireproof paper?
Don't be too fast to jump in!
Matching above the bottom pipes creates a red lantern which you need to float up with additional matches to block the top pipe from spawning lava.
Dev tip: You need to score 100,000 points - don't be too fast to block both pipes. Be careful not to destroy a blocking lantern! If you get the chance create a second lantern below it, just in case you get a red gem on the outside edge.