This story appears in the January 2012 issue of National Geographic magazine.
It was like a scene conjured by a Hollywood special effects shop. In September 2005 Afar herders in northern Ethiopia watched in amazement as the Earth yawned open and swallowed their goats and camels. Chunks of obsidian burst from subterranean caverns and flew through the air, said one local, "like huge black birds." For three days a cloud of billowing ash dimmed the sun as the region's largest volcano, Erta Ale—"smoking mountain" in the Afar language—erupted.
What set off these startling events? Miles below the surface a mammoth burp of magma had welled up between two tectonic plates, prying them farther apart. Aboveground, hundreds of faults and fissures opened along a 40-mile stretch of desert, swallowing unlucky livestock. More than a dozen smaller burps have shaken the area in the years since.
East Africa's Afar depression is one of the world's most geologically hyperactive regions. Fly over it in an airplane—or in a one-person motorized paraglider, as photographer George Steinmetz did countless times—and it may appear as frozen and still as Arctic ice. But the Afar's timeless visage hides its true nature. Below the surface, Earth's rocky rind is ripping apart, and underground chambers of magma are fueling 12 active volcanoes as well as steaming geysers, boiling cauldrons, and a fiery lake of lava.
The 2005 quakes and subsequent rattlings are the latest in a long series of seismic upheavals that started some 30 million years ago, when magma pushed through the Earth's crust and began splitting the Arabian Peninsula from Africa, creating the Red Sea and the Gulf of Aden. As the upwelling magma cools, it becomes denser and sinks. Some parts of the Afar now sit more than 500 feet below sea level.
Because of its low elevation, the Afar depression has been repeatedly flooded by the Red Sea, most recently about 30,000 years ago. After each incursion, the seawater evaporated, leaving behind thick layers of salt. This "white gold" has long been an important source of income for the Afar people, who remain fiercely loyal to this extreme land despite summer temperatures that can soar above 120 degrees Fahrenheit.
Scientists brave the desert's hardships for a different reason. The Afar is one of the few places on Earth where an undersea ridge—a jagged volcanic seam where magma oozes up and becomes new seafloor—emerges on land. This offers earth scientists the rare chance to study geologic processes that normally unfold far below the surface of the ocean.
Given enough time—at least several million years—those processes will produce dramatic changes in the geography of Africa: The Afar depression and the entire Great Rift Valley will cradle a new sea that connects the Red Sea to the Indian Ocean and cleaves the Horn of Africa from the continent.