There are few things quite as tense as watching one volcanologist mutter, "Oh my god. He's crazy. He's crazy," while watching another volcanologist scramble around the edge of a caldera.

It only gets more tense when you realize that the volcano in question is Nyiragongo in the Democratic Republic of the Congo—which has some of the fastest-moving lava flows ever recorded. The key feature of Nyiragongo is that lake of lava in the center of the crater that you see in the video. In January 1977, the lava lake was 2000 feet deep. When the volcano erupted later that month, the lake emptied dry in less than an hour. Lava was clocked at 40 mph.

Video clip from the BBC's "Journey to the Center of the Planet"

More about the program this came from.

Via EstudandoGeologia and Chris Rowan