Seen from afar, the peaks of the Virunga Mountains stand in awe-some magnitude in a mist of clouds. Rising sharply to dominate the plains of Rwanda, Uganda and the Democratic Republic of Cango, these mountains evoke a spine-tingling awareness of the Earth’s origins. Eight volcanoes spread over 36 miles (58km) make up the Virunga range. Six of them are mute and extinct; the other two are active, forever smouldering with the threat of eruption.
Nyamulagira, meaning ‘commander’, is one of the world’s most active volcanoes. Europeans first witnessed an eruption in 1894, and since then it has erupted several times through cracks along its sides. During a spectacular eruption in 1938-40, lava from a pool on the volcano’s flank ran down to lake Kivu, 15 miles (24km) away.
An observer noted that the lava glowed ‘like slag from a furnace’ as it flowed, and that ‘enormous clouds of steam were generated where the lava met the waters of the lake. The loss of so much lava led to the collapse of Nyamulagira’s summit, leaving a massive crater over a mile (2km) across.
An impressive crater also crowns the neighbouring active volcano of Nyiragongo. In 1977 its near-perfect cone split into five places, spilling out molten lava which destroyed everything in its fiery path as it moved downhill. Spills of lava from the Virungas have helped to shape the surrounding landscape. The mountains lie in the western branch of Africa’s Great Rift Valley. At one time the rivers of this branch drained north towards the Nile, but lava flows from the volcanoes are thought to have dammed the rivers to produce Lake Kiyu. With its deeply indented shore, Lake Kivu is regarded by many as the most beautiful of Africa’s lakes, but despite the sleeping beauty of the water, the lake is a time bomb.
Carbon dioxide seeps through the bed of the lake and accumulated there, trapped by the enormous pressure of the water above – the lake averages about 600ft (180m) in depth, but in places is as deep as 1300ft (400m). When the same conditions arose in Lake Ntos in Cameroon in 1986, a deadly cloud of carbon dioxide suddenly burst through the water and settled like a suffocating blanket over densely population valleys, killing more than 1700 people.
At Lake Kivu, the consequences could be even more devastating, for bacterial action is converting the carbon dioxide into methane. Human interference with the lake, such as pumping up methane to use as fuel, could cause the gas to bubble to the surface of the water. Once there, contact with a naked flame would turn the flammable gas into an explosive fireball, incinerating the surrounding area.
Upheavals in the Earth’s crust pose no threat elsewhere in the Virunga Mountains, for the other volcanoes have long been extinct. Karisimbi, the highest point at 14,787ft (4507m), takes its name from Nsimbi – meaning ‘white cowrie shell’ – an allusion to the snow which often covers the top of the mountain. The slopes of nearby Bisoke are the home of the mountain gorilla, Sabinyo, near the eastern end of the Virunga, crowned by several peaks, on the highest of which the boundaries of the Democratic Republic of Congo, Rwanda and Uganda meet.