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January 2003

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Ol Doinyo Lengai

By Joel K. Bourne, Jr.

Wings of Stone
Unusually cool and highly fluid lava produces a Dr. Seussian world of geologic whimsies, like this hours-old extrusion frozen in midair. As fragile as a child's drip castle and nearly as short-lived, such bizarre formations result from the world's only active natrocarbonatite flows, which have a chemical composition akin to laundry soap. Exposed to the atmosphere, the lava rapidly hardens and decays. This foot-long wing took flight and shattered within 48 hours.
Mountain of God
Home to the Masai god, Eng'ai, who signals her wrath with eruptions and drought, Ol Doinyo Lengai's current summit rises 7,650 feet (2,332 meters) above the parched Rift Valley floor, overshadowing the inactive southern crater, top right, that had built most of the young volcano by 15,000 years ago. Pointed hornitos and grayish flows mark recent activity.
"Lava was raining down like hailstones."—Carsten Peter
Some people like to climb big granite walls, others frozen waterfalls. Photographer Carsten Peter and his climbing partner Chris Heinlein like to climb erupting hornitos, the sharp, extremely steep hollow pinnacles that sometimes form around active vents. "You can't compare it to normal rock," says Peter of this 50-foot (15.2 meters) hornito, or spatter cone. "It's very fragile and very unstable. The cone was rumbling and vibrating, but a rock plate was directing the lava in the other direction." His advice: "Don't try this at home."
Though Ol Doinyo Lengai's fresh natrocarbonatite lavas—which erupt at around 1,000 degrees Fahrenheit (538 degrees Celsius)—are roughly half as hot as more common basalt lavas, the spattering drops of molten rock will still burn through a cotton jumpsuit like a cigarette through nylons. Yet the dramatic mountain in a remote, little-visited corner of Tanzania invites close inspection, especially from volcanologists. The late photographer and renowned volcano chaser Katia Krafft was captivated by what she called the "toy volcano" because its diminutive flows are cool enough to collect with a spoon. "It's a perfect little laboratory volcano," agrees Barry Dawson of the University of Edinburgh, the first to study the strange lavas, in 1960, for the Tanzania Geological Survey. "The shape and style of the extrusions exactly mimic the flows of basaltic volcanos, except the latter are so much bigger."
Ol Doinyo Lengai (pronounced ol doyn-yo len-guy) is Masai for "Mountain of God." It is a place of pilgrimage for Tanzania's famous pastoralists, who often make the long journey to entreat their god, Eng'ai, for the most important things in their world: rain, cattle, and children. In one of the more common rituals, a Masai elder leads a group of barren women to the base of the mountain, where they pray to Eng'ai to bless them with a child.
Whatever its power, the mountain casts a strong spell over all who visit. "It's absolutely incredible. Like being on the moon," says geographer Celia Nyamweru of St. Lawrence University in upstate New York, who has climbed the mountain a dozen times. Carsten Peter, who has spent a career dodging lava bombs around the world, has climbed it four times in the past 11 years. "I'm addicted to that volcano," he says.
Frozen in  Flight
Hardening within seconds of extrusion, volcanic froth rich in carbon dioxide spews from an active vent. What begins as liquid lava hits the ground with the tinkling of breaking glass. "The big drops were forming little parachutes," says Carsten Peter. "It looked like silver flying through the air."

Little Rock Candy Mountain
Like a river of melted chocolate, a fresh lava flow less than a yard wide pours from a collapsed spatter cone. Unlike common basalt lavas, which are sticky with silica, Ol Doinyo Lengai's natrocarbonatite lavas are mostly slick sodium carbonate. As a result they have the lowest viscosity of any lava, roughly the same runniness as olive oil.
Quicksilver to Ash
A serpentine flow barely six inches (15 centimeters) wide and 50 feet (15 meters) long meanders through formations of smooth pahoehoe lava and rough aa lava, the same forms common in basalt lavas. Ol Doinyo Lengai's lavas break down so quickly that their age can be judged by their color. Black as oil when they emerge, they quickly shift to muddy browns, grays, and finally frosty white within a few days. Looking like a spotted salamander frozen in stone, a pahoehoe flow reveals the lava's fragility: Even raindrops accelerate its decomposition.
The interior of a collapsed hornito hides a lava lake. Carbon dioxide in the lava creates bubbles the size of basketballs that slowly expand, then burst, plastering the rim with spray. This splatter builds the foundation of a new cone.
Fire in the Hornito
On a moonlit night atop Ol Doinyo Lengai, Carsten Peter couldn't sleep for all the volcanic activity around him. He climbed toward an erupting hornito, set up his camera, and held the shutter open as the lava surged forth. The volcano's lavas are barely red to the naked eye. But this long exposure captured the lava's hidden glow—and a bit of the mountain's magic.


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