Definitely don't try this at home (or if you happen across a volcanic vent), but if you've ever wondered what would happen if you pressed down on hot lava, this video is a must-watch. It's a great lesson in how the reality of lava differs from the way many people think of the substance.
Alex Rivest posted this video, which was taken at the volcano Kilauea on the Island of Hawaii. He explains that when lava emerges from one of the volcano's vents, it comes out at 700 to 1,200 °C. He also points out that the foot presses on the lava rather than sinking into it because of the density of the lava:
This video shows how pressure applied to this dense material only causes a slight indentation. While this may not be surprising (it is liquid rock), I think that many people think of lava as more of a hot-watery-like substance. You would never fall into a lava lake the way you would a swimming pool, the molten rock is much more dense, so you would simply land on it, sink a little, and be burned.
We're also assured that this demonstration was performed by a professional. What kind of professional, we're not entirely sure.
Rivest also has some pretty stunning photos of volcanos on his own website.