Answer: Lava

Forget everything you’ve seen in movies, cartoons, and video games. If you ever find yourself thrown into the cauldron of an angry volcano, you will not sink down into the fiery pool like a drowning swimmer. Given the reality of the situation, however unfortunate it might seem, that would be a preferable alternative.

Lava, unlike how it is popularly depicted, actually has a density much higher than water and the human body. On top of that, it’s highly viscous and has more in common, in that regard, with peanut butter than water. As such, you wouldn’t sink as much as you would lay atop it like an egg in a frying pan.