TV Program Description
Original PBS Broadcast Date: November 1, 2005

Volcano Under the City Homepage

Deep inside a volcano, a team of scientists camps amid rockslides and seething sulfur dioxide gas. Their mission: to study this deadly mountain up close to find out what makes it tick. The fate of nearly half a million people in a nearby city could be at stake. NOVA accompanies this daring expedition in "Volcano Under the City."

The volcano is eastern Congo's Mount Nyiragongo, which erupted in January 2002, surprising the city of Goma 11 miles away. Enormous cracks opened in the ground nearby and spewed fountains of lava, killing 100 people and leaving 120,000 homeless. Scientists' biggest fear is that next time a fracture could open under the city itself.

Molten lava is not the only worry. Gas vents associated with the fractures release carbon dioxide, which is colorless, odorless, and heavier than air. Anyone venturing into a lowland area filled with the gas can lose consciousness before realizing the danger and asphyxiate. Children are the most frequent victims of these deadly emissions, which the local people call mazukus, or evil winds.

Similarly, carbon dioxide is leaking into nearby Lake Kivu and being absorbed by the water. The dissolved gas now sits harmlessly at the bottom of the lake, but it could be catastrophically released under certain conditions. This happened at Lake Nyos in Cameroon, West Africa, in 1986, killing 1,800 people. If something similar happened at Lake Kivu, which is much larger, it could suddenly end hundreds of thousands or even millions of lives.

Leading the effort to help Congolese scientists understand Nyiragongo are French volcanologist Jacques Durieux and Italian geochemists Dario Tedesco and Orlando Vaselli. "Volcanology is a multi-disciplinary approach," says Vaselli. "What I'm dealing with is mainly chemical analysis of gases." He adds that a complete picture of the volcano requires studying its prior history, its seismic activity, the temperature variations and chemical makeup of its gases, and the composition of its lava.

Analysis of fresh lava is important since the lava's crystalline structure can reveal whether magma is coming up from deep within the Earth or if it is shallow rock being melted by rising hot gases. Magma from a deep source is fresh, very gassy, tends to be extremely liquid, and can be released in massive quantities, while magma formed closer to the surface tends to be less gassy and more viscous. (For more on what makes this particular volcano tick, see Anatomy of Nyiragongo.)

The quest for good data about Nyiragongo takes the team on its most daring expedition—into the belly of the volcano itself. Climbing to the top of Nyiragongo, they look down into a crater that is more than twice the height of the Empire State Building. Using ropes, they descend halfway down and set up camp on a ledge rimming a deep pit with a cauldron of bubbling lava at the bottom. (For more on the expedition, see Behind the Scenes.)

From here they collect gas samples and devise a plan to snatch a fresh sample of the lava. Their strategy is to pull a rope across the pit and then attach a steel cable with a chain and hammer dangling at the end. Using a pulley, they lower the cable toward the lava fountain, many hundreds of feet below. Durieux is in charge of the operation and at a crucial moment feels a tug on the cable. "It's biting like a fish," he says, breathless amid the smoke and fumes of a restless giant.