Here's the thing about dying in lava, which everyone seems to fuck up: You do not sink into like you're in a swimming pool (looking at you, Gollum from Lord of the Rings). You do not instantly melt into goo on contact (Volcano subway guy). Density and viscosity doesn't work that way. Just let Wired explain to you the right way to die in lava.
Lava is much denser than water, at 3100 kilograms per cubic meter vs 1000 for H2O, and is also more viscous, 100,000 to 1 million times so, meaning it yields to your body much less readily. So when you hurl yourself into a pool of molten rock, you're more like a piece of Styrofoam floating on a pool of motor oil than a surfer falling off his board. You'd stay afloat. Then you'd burst into flames, since molten lava is more than 1,000 degrees Celsius. So you'd be more flaming and charring than melting.
Anyway, be sure to file this information away in your "how to die properly" file. You may well need it the next time you have to accompany a pedantic scientist to an action/adventure film.