There's a passage about 'rivers of molten rock that wound their way... until they cooled and lay like twisted dragon-shapes vomited from the tormented earth.' That's a perfect description: how did Tolkien know, a quarter century before anyone ever saw a picture of Io? Talk about Nature imitating Art.
2010: Odyssey Two (ed. RosettaBooks, 2012) - ISBN: 9780795324826