© Tobias Fischer/University of New Mexico Façade. Thin and runny lava called carbonatite tops the Ol Doinyo Lengai volcano in Tanzania.
Ol Doinyo Lengai is a maverick. Of Earth's hundreds of active volcanoes, it's the only one currently producing a black, runny lava instead of the familiar goopy, glowing red stuff. Now, an international team of researchers thinks it has found the explanation for the unusual behavior of the Tanzanian volcano, which has to do with its location and the future of the African continent.
Africa is fracturing. Everything east of the Great Rift Valley--a 6000-kilometer gash that runs from Syria to Mozambique--is imperceptibly moving into the Indian Ocean. The valley itself is slowly sinking, and millions of years from now it will rest on the sea floor. Smack-dab in the middle of the valley sits Ol Doinyo Lengai, a classic volcanic cone rising nearly 3000 meters. But the mountain's eruptions are anything but classic. Its lava, called carbonatite, is nearly free of silicon oxide, which in sufficient quantity produces the blazing-hot, flame-red flows people typically associate with volcanoes. Instead, Ol Doinyo Lengai's carbonatite lava is much cooler--only about 500°C, compared with 1000°C or more for conventional eruptions. It also flows easily and rapidly, more like water than lava. Initially, the carbonatite is black but turns white quickly after exposure to rain and surface water.
