You can’t sink in lava and die as depicted in most movies, because it’s too dense!

Peter Jackson got the scene where Gollum falls into Mount Doom totally wrong in Lord of the Rings. A person doesn’t sink in lava like they were in a swimming pool or quick sand. Neither do you melt into goo upon contact with the lava. 

Movies depict lava deaths completely erroneously. Lava is much denser than water. To be precise, lava is 3100 kilograms per cubic meter versus water at 1000 kilograms per cubic meter. Lava is also a 100,000 to 1 million times more viscous than water. 

Because of this, Lava yields to solid bodies much less than water does. So, when you fall into a pool of lava, you are more like a Styrofoam floating on a pool of motor oil. You would float on top of the molten rock. Then, you’d burst into flames, because lava is more than 1000 degrees Celsius.

If you're considering jumping into a pool of lava, just be aware that you're not in for a toasty swim, but rather, you might just die on impact. 

(Source)