Board Thread:Questions and Answers/@comment-34623718-20180208021138/@comment-1955501-20180215185454

The Leidenfrost effect is correct, yes. Basically the water absorbs the heat of the lava, but it can only absorb so much heat before it turns to steam, and the steam forms a sort of protective barrier that separates the lava from the surrounding water. So while the water does cool off the lava a bit, it still takes a lot of water and a long time to cool it down to rock.