Major Volcanoes of the World

Mount Nyiragongo

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 19 km north of the town of Goma and the Lake Kivu and just west of the border with Rwanda. The main crater is 250 m deep, two km 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 1882, it has erupted at least 34 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 cinder 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 (up to 100 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.
Nyiragongo is most famous for its semi permanent lava lake, which was discovered by French vulcanologist Haroun Tazieff.