Mount Nyiragongo
| Mount Nyiragongo | |
|---|---|
 Lava lake in the crater of Mount Nyiragongo |
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| Elevation: | 3,470 metres (11,384 feet) |
| Location: | Democratic Republic of the Congo |
| Range: | Virunga Mountains |
| Coordinates: | 1°31′0″S, 29°15′0″E |
| Type: | Stratovolcano |
| Age of rock: | |
| Last eruption: | 2005 (continuing) |
Mount Nyiragongo is a volcano in the Virunga Mountains associated with the Great Rift Valley. It is located in the Democratic Republic of the Congo, about 19km north of the town of Goma and the Lake Kivu and just west of the border with Rwanda. The main crater is 250m deep, 2km wide and sometimes contains a lava lake. Nyiragongo and nearby Nyamuragira are together responsible for 40% of Africa's historical volcanic eruptions.
Geology
Not much is known about how long the volcano has been erupting, but since 1883, it has erupted at least 15 times, including many periods where activity was continuous for years at a time, often in the form of a churning lava lake in the crater. The volcano partly overlaps with two older volcanoes, Baratu and Shaheru, and is also surrounded by hundreds of small volcanic cones from flank eruptions.
Volcanism at Nyiragongo is caused by the rifting of the Earth's crust where two parts of the African Plate are breaking apart. A hot spot is probably also partly responsible for the great activity at Nyiragongo and Nyamuragira.
The lava emitted in eruptions at Nyiragongo is often unusually fluid. Nyiragongo's lavas are made of melilite nephelinite, an alkali-rich type of volcanic rock whose unusual chemical composition may be a factor in the unusual fluidity of the lavas there. Whereas most lava flows move rather slowly and rarely pose a danger to human life, Nyiragongo's lava flows may race downhill at up to 60 miles per hour (97 km/h). This is because of the extremely low silica content (the lava is mafic). Hawaiian volcanic eruptions are also characterised by lavas with low silica content, but the Hawaiian volcanoes are broad, shallow-sloped shield volcanoes in contrast to the steep-sided cone of Nyiragongo, and the silica content is high enough to slow most flows to walking pace.
1977 eruption
Between 1894 and 1977 the crater contained an active lava lake. On 10 January 1977, the crater walls fractured, and the lava lake drained in less than an hour. The lava flowed down the flanks of the volcano at speeds of up to 60 miles per hour on the upper slopes, overwhelming villages and killing at least 70 people. Some reports quote much higher figures of up to several thousand people. The hazards posed by eruptions like this are unique to Nyiragongo. Nowhere else in the world does such a steep-sided stratovolcano contain a lava lake containing such fluid lavas. Nyiragongo's proximity to heavily populated areas increases its potential for causing natural disasters. The 1977 eruption raised awareness of the unique dangers posed by Nyiragongo, and because of this it was designated a Decade Volcano, worthy of particular study, in 1991.
The 1977 eruption was preceded by the creation of a new small volcano, Murara, a short distance away on the slopes of Mount Nyamuragira.
2002 eruption
Lava lakes reformed in the crater in eruptions in 1982- 1983 and 1994. Another major eruption of the volcano began on January 17, 2002, after several months of increased seismic and fumarolic activity. An 18 km fissure opened in the south flank of the volcano, spreading in a few hours from 2800 m to 1550 m elevation.
The fissure emitted three streams of lava, one of which flowed through the city of Goma. 400,000 people were evacuated from the city during the eruption. Lava also destroyed Goma Airport, and reached nearby Lake Kivu. This raised fears that the lava might cause gas-saturated waters deep in the lake to suddenly rise to the surface, releasing lethally large amounts of carbon dioxide and methane - a similar event to the disaster at Lake Nyos in Cameroon in 1986. This did not happen, but volcanologists continue to monitor the area closely.
About 45 people died in the eruption, but property damage was extensive. At least 15% of Goma was destroyed, leaving about 120,000 people homeless. The eruption was the most destructive effusive eruption in modern history.
Six months after the start of the 2002 eruption, Nyamuragira volcano also erupted. Activity at Nyiragongo is ongoing, but currently confined to the crater, where another lava lake has formed about 250 metres below the level of the 1994 lava lake.