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 (10,660 ft) prior to the January 1977 eruption – a lake depth of about 600 m (2,000 ft). Following the January 2002 eruption, the lava lake was recorded at a low of about 2,600 m (8,500 ft), or 900 m (3,000 ft) below the rim.[2] The level has gradually risen since then.[3] Nyiragongo and nearby Nyamuragira are together responsible for 40% of Africa's historical volcanic eruptions.[4]
Geology
Nyamuragira (left) and Nyiragongo (right). Vertical scale exaggerated (1.5×).
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.[citation needed]
Nyiragongo's cone consists of pyroclastics and lava flows.[5] Nyiragongo's lavas are low-silica, alkali-rich, ultramaficextrusive 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.[5][6][7] 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 (60 mph).[8]
Active history
Not much is known about how long the volcano has been erupting, but it has erupted at least 34 times since 1882, 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.[9] At that time, it was measured at nearly 120,000 square metres (1.3×10^6 sq ft).[9] Subsequent expeditions showed that the lake fluctuated in size, depth, and temperature over time.[9]
The lava lake activity is ongoing.[10][3][11] As of 2020[update], the lake is mostly confined within a broad, steep-sided cinder cone (roughly 18 m (60 ft) high by 180 m (600 ft) wide) on the crater floor.[11][12]
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.[1] The lava flowed down the flanks of the volcano at speeds of up to 60 km/h (37 mph) on the upper slopes, the fastest lava flow recorded to date,[13] overwhelming villages and killing at least 50 people in the villages of Kibati and Moniki, according to reports made at the time. [14]
Within 30 minutes, the lava lake had emptied, flowing north, south, and west of the volcano. Nowhere else in the world does such a steep-sided stratovolcano contain a lake of such fluid lava.[citation needed] Nyiragongo's proximity to heavily populated areas increases its potential for causing a natural disaster. The 1977 eruption raised awareness of the unique dangers posed by Nyiragongo, and because of this, in 1991 it was designated a Decade Volcano, worthy of particular study.[15]
The 1977 eruption was preceded by the creation of a new small volcanic vent, Murara, a short distance away on the slopes of Nyamuragira.[16]
2002 eruptions
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 (8.1 mi) fissure opened in the south flank of the volcano, spreading in a few hours from 2,800 to 1,550 metres (9,190 to 5,090 ft) 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 (660 to 3,280 ft) wide and up to 2 metres (6 ft 7 in) 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.[17] 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[18] – similar to the disaster at Lake Nyos in Cameroon in 1986. This did not happen, but volcanologists continue to monitor the area closely.[19]
About 245 people died in the eruption from asphyxiation by carbon dioxide and buildings collapsing due to the lava and earthquakes.[20] Lava covered 13 percent of Goma, about 1.8 square miles (4.7 km2),[21] and nearly 120,000 people were left homeless.[2]
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.[17]
Six months after the start of the 2002 eruption, Nyiragongo volcano erupted again.
Satellite image of the eruption plume from Nyiragongo in July 2004
Mount Nyiragongo's lava lake
Ongoing threat
Localized carbon dioxide toxicity, known locally as 'mazuku', has killed children even more recently. In locations where the gas seeps from the ground at relatively high levels, without the dispersing effects of wind, its effects can be deadly.[22] On 8 March 2016, Goma Volcano Observatory discovered a new vent that opened in the northeast edge of the crater, following local reports of rumblings coming from the volcano. Some fear that this could lead to a flank eruption.[23] Observers in 2020 witnessed a rise in the lava lake and other signs of an impending eruption. [11]
An eruption began on 22 May 2021.[24] Lava approached the Goma airport and moved towards the city centre of eastern Goma.[citation needed] It was later confirmed by the North Kivu province's military governor that the eruption was at around 17:00 GMT.[25] A highway to Beni was cut off by lava, and authorities urged residents from the city of Goma to evacuate, causing thousands of people to leave their homes.[26][27] There was also an electricity cut across large areas following the eruption. [28] As of 27 May 2021, 37 people were missing and presumed dead, after a lava flow reached the outskirts of the city of Goma.[29] The eruption resulted in at least 32 deaths, mostly caused by car crashes in the ensuing evacuation.[30][31]
Monitoring
Satellite image of Nyiragongo's lava lake in July 2018
The volcano is continuously monitored by a team of scientists at the Goma Volcanic Observatory (GVO), with seismic data produced every four minutes and temperature data produced every ten minutes.[19] Continued funding for the GVO is in doubt, as the World Bank decided in 2020 to terminate its contributions.[11]
^ abSahama, Thure Georg (1978). The Nyiragongo main cone. Musée Royal de l'Afrique Centrale, Tervuren, Belgique: Annales – Serie in 8° – Sciences Géologiques, volume 81. Tervuren, Belgium: Royal Museum for Central Africa / Musée Royale de l'Afrique Centrale. OCLC434026615.
^Sahama, Thure Georg (1962). "Petrology of Mt. Nyiragongo: a review". Transactions of the Edinburgh Geological Society. 19 (1): 1–28. doi:10.1144/transed.19.1.1. S2CID130469613.
^ abcScheffel, Richard L.; Wernet, Susan J., eds. (1980). Natural Wonders of the World. United States of America: Reader's Digest Association, Inc. pp. 272–273. ISBN978-0-89577-087-5.
^"Volcano Deaths Estimated at 50", AP report in Omaha World-Herald, January 15, 1977, p.6; A brief sentence in a BBC online report more than 40 years after the event ("The volcano's deadliest eruption happened in 1977, when more than 600 people died") is not supported by reports made in the first few years after the event.
^Nakamura, Y.; Aoki, K. (1980). "The 1977 eruption of Nyiragongo volcano, eastern Africa, and chemical composition of the ejecta". Bulletin of the Volcanological Society of Japan (in Japanese). 25 (1): 17–32. doi:10.18940/kazanc.25.1_17. (English abstract)
Allard P, Baxter P, Halbwachs M, Kasareka M, Komorowski JC, Joron JL (2003). "The most destructive effusive eruption in modern history: Nyiragongo 2003". Geophysical Research Abstracts. 5: 11970.
Demant A, Lestrade P, Lubala RT, Kampunzu AB, Durieux J (1994). "Volcanological and petrological evolution of Nyiragongo volcano, Virunga volcanic field, Zaire". Bulletin of Volcanology. 56 (1): 47–60. Bibcode:1994BVol...56...47D. doi:10.1007/BF00279728. S2CID129031508.
