If volcanologists invent an instrument that can measure the interplay of beauty and menace, Nyiragongo, on the eastern edge of the Democratic Republic of the Congo, in the province of North Kivu, will send its needle into spasms. Twenty thousand years after it formed, Nyiragongo is still terribly Pleistocene in appearance: Its cone curves gently through montane forest and then thrusts two miles into the sky, where its rim is only occasionally visible through the wooly mists above Goma, the city it watches over and periodically destroys. The crater's emissions give the mists green, amber, and crimson tones. The people who once lived around the volcano believed the souls of evildoers were cast into the crater. When the souls