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Mount Nyiragongo is an active stratovolcano with an elevation of 3,470 m in the Virunga Mountains associated with the Albertine Rift.
It is located inside Virunga National Park, in the Democratic Republic of the Congo, about 12 km north of the town of Goma and Lake Kivu and just west of the border with Rwanda. The main crater is about two kilometres wide and usually contains a lava lake. The crater presently has two distinct cooled lava benches within the crater walls -one at about 3,175 m and a lower one at about 2,975 m.
Nyiragongo's lava lake has at times been the most voluminous known lava lake in recent history. The depth of the lava lake varies considerably. A maximum elevation of the lava lake was recorded at about 3,250 m prior to the January 1977 eruption -a lake depth of about 600 m.
Following the January 2002 eruption, the lava lake was recorded at a low of about 2,600 m, or 900 m below the rim. The level has gradually risen since then.
Nyiragongo and nearby Nyamuragira are together responsible for 40 per cent of Africa's historical volcanic eruptions.
The volcano partly overlaps with two older volcanoes, Baruta and Shaheru, and is also surrounded by hundreds of small volcanic cinder cones from flank eruptions.
Nyiragongo's cone consists of pyroclastics and lava flows.
Nyiragongo's lavas are low-silica, alkali-rich, ultramafic extrusive rocks essentially free of feldspars. They range from olivine-rich melilitites through leucites to nephelinites, containing, in various proportions mainly the minerals nepheline, leucite, melilite, kalsilite, and clinopyroxene. This very low silica composition results in eruptions with unusually fluid flows. 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 100 km/h.
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 existence of the lava lake had been suspected for some time but was not scientifically confirmed until 1948.
More information: Smithsonian-Global Volcanism Program
Lava lakes reformed in the crater in eruptions in 1982-1983 and 1994. Another major eruption of the volcano began on 17 January 2002, after several months of increased seismic and fumarolic activity.
A 13 kilometres fissure opened in the south flank of the volcano, spreading in a few hours from 2,800 to 1,550 metres elevation and reaching the outskirts of the city of Goma, the provincial capital on the northern shore of Lake Kivu.
Lava streamed from three spatter cones at the end of the fissure and flowed in a stream 200 to 1,000 metres wide and up to 2 metres deep through Goma. Warnings had been given and 400,000 people were evacuated from the city across the Rwandan border into neighbouring Gisenyi during the eruption.
Lava covered the northern end of the runway at Goma International Airport, leaving the southern two-thirds usable, and reached 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 -similar to the disaster at Lake Nyos in Cameroon in 1986. This did not happen, but volcanologists continue to monitor the area closely.
About 245 people died in the eruption from asphyxiation by carbon dioxide and buildings collapsing due to the lava and earthquakes.
Lava covered 13 per cent of Goma, about 4.7 km2, and nearly 120,000 people were left homeless.
Immediately after the eruption stopped, a large number of earthquakes were felt around Goma and Gisenyi. This swarm activity continued for about three months and caused the collapse of more buildings.
Six months after the start of the 2002 eruption, Nyiragongo volcano erupted again.
More information: National Geographic
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