From the Annals of Bad Ideas comes this story and video of a man walking up a lava flow on Sicily's Mt. Etna, from Erik Klemetti, a geoscientist at Denison University in Ohio and author of Wired's Eruptions Blog.
In the video (above), the man takes about five (naturally, very quick) steps up a small channel of flowing lava. In his post, Klemetti breaks down how this is possible: For one, the lava appears to be a highly viscous type, which means that it is less likely to yield as much when you push down on it, Klemetti writes, unlike, say, water in a stream. It also seems fairly cool, with a dark crust on top (that forms because the extremely hot lava meets the relatively cool air. The lava flow also appears to be a small channel, with hardened, cooled lava around it. All of those factors combined to let the man sprint up the slope unscathed.
BUT — not surprisingly — walking up a lava flow is still a really, really bad idea. If you watch the video closely, so you can see a flash under the man's shoe when he takes his final step on the flow. That's probably his shoe combusting — combusting! — from the heat of the flow, Klemetti said. (And he has first-hand experience, having sampled lava at Hawaii's Kilauea volcano and barely being able to handle the heat from standing near a flow there.) Speaking of Kilauea, the lava lake atop its Halema'uma'u crater actually does have lava as light as water, so stepping on the lava there might be an even worse idea.
Klemetti has also addressed whether a person stepping in hot lava would sink a la Gollum in "Lord of the Rings: Return of the King." You'll have to read to find the answer.
And because it can't be said too many times: Please don't try to walk on lava!