Background information


Located in Central Africa's Democratic Republic of the Congo, Mount Nyiragongo is a volcano with a summit elevation of 3,470 meters. (1) Mount Nyiragongo is located in the Virunga Mountains, about 19 km north of the town of Goma and Lake Kivu, just west of Rwanda's border (Figure 1). (2)
Figure 1 - Regional Map of Central Africa. (6)
Figure 1 - Regional Map of Central Africa. (6)
Nyiragongo is a stratovolcano, also known as a composite cone, which is the most picturesque and the most deadly of the volcano types. Nyiragongo possesses gentle lower slopes, but it rises steeply near the summit to produce an overall structure that is concave in an upward direction (Figure 2). (3) The summit area contains a 1.2-km-wide summit crater. (1)
Figure 2 - Photo of Nyirangongo rising above Lake Kivu. (1)
Figure 2 - Photo of Nyirangongo rising above Lake Kivu. (1)
Scientists are unclear about how long the volcano has been erupting. Since 1882, it has erupted a minimum of 34 times. Many periods existed where activity was continuous for years, often in the form of a 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. (2) Volcanism at Nyiragongo can be explained by the rifting of the Earth's crust. This is where two parts of the African Plate are spreading apart. A hot spot is also partly accountable for the massive turmoil at Mount Nyiragongo. (4)


What is a Lava Lake?


A lava lake is a lake of molten lava, usually basaltic, in a volcanic crater or depression. The term refers to solidified and/or partially solidified stages as well as to the molten, active lava lake (Figure 3). (8) This is a large pool of lava, produced around a vent when lava fountains spew forth large amounts of lava in a short period of time. The term basaltic refers to a dense, hard, dark volcanic rock constructed mostly of plagioclase, pyroxene, and olivine, and often having a glassy appearance when cooled. (9) Nyiragongo is most famous for its semi permanent lava lake, which was discovered by French volcanologist Haroun Tazieff. (2)


Figure 3 - Picture of Nyiragongo's Lava Lake.(7)
Figure 3 - Picture of Nyiragongo's Lava Lake.(7)




Hazards Posed By Nyiragongo


Figure 4 - Lava Flows form Nyiragongo.(8)
Figure 4 - Lava Flows form Nyiragongo.(8)
The lava produced by this volcano during eruptions is typically fluid. The lava from Nyiragongo is made of melilite nephelinite, an alkali-rich volcanic rock whose chemical composition may be a factor in the unusual fluidity of the lavas there. (1) Most lava flows are slow moving and infrequently inflict a danger to human life. Nyiragongo's lava flows can sprint downhill at up to 100 km/h, as it did in 2002. (Figure 4) (4) This occurs due to the tremendously low content of silica. (1) The lava is considered mafic, meaning that before cooling, it has a low viscosity due to the lower silica content. Water and other volatiles can more easily and gradually escape from mafic lava, so eruptions of volcanoes made of this type of lava are less explosively violent than other types of lava eruptions. (5)

Nyiragongo poses many potential hazards other than lava flows, such as Mazukus (meaning "Evil Winds" in Swahili), which occur in low lying locations with dry CO2 vents, volcanic ash, phreatomagmatic (a volcanic explosion that extrudes both magmatic gases and steam; it is caused by the contact of the magma with groundwater or ocean water). eruptions from the high water table, earthquakes and the possibility of the degassing of Lake Kivu. (10) Lake Kivu, scientists say, is a massive pool of methane and carbon dioxide that lies at the bottom of the deep-water lake. (12) Experts warn the gases might one day explode or burst to the surface, releasing a deadly cloud similar to one that killed more than 1,700 people at Cameroon’s methane-rich Lake Nyos in 1986. (12)



Figure 5 - Vent near Nyiragongo.(13)
Figure 5 - Vent near Nyiragongo.(13)
Nyiragongo has a reputation for discharging large amounts of sulfur dioxide through its numerous vents. At up to 50,000 tons each day, this is more than any other active volcano, and it presents a serious health hazard to people and animals living in proximity (Figure 5). (13)







Figure 6 - Fissure near Nyiragongo.(13)
Figure 6 - Fissure near Nyiragongo.(13)
On the exterior surface of volcanoes, a fissure is an elongated fracture from which lava emits. Nyiragongo has a complicated system of fissures, some of which extend from its crater, at the summit, all the way down to the city of Goma on its lower side. Without warning, lava can burst out of these fissures. It is thought, by scientists, that a fissure could become exposed directly beneath Goma in a future eruption (Figure 6). (13)





Figure 7 - Dike near Nyiragongo.(13)
Figure 7 - Dike near Nyiragongo.(13)

Dikes are imaginable as the veins of a volcano, the pathways of rising magma. A dike is a more or less vertically flat, sheet-like magma body that cuts, nonconforming, through older rocks or sediments. Most dikes can be described as fractures into which magma intrudes or from which they might erupt. Hundreds of dikes can penetrate the inner core of a volcano, as they do in Nyiragongo (Figure 7). (13)





Past Eruptions


Two notable eruptions of Mount Nyiragongo occurred in the past three decades, 1977 and 2002.

1977

Figure 8 - Lava Flow from the 1977 Nyiragongo Eruption. (15)
Figure 8 - Lava Flow from the 1977 Nyiragongo Eruption. (15)
Between 1894 and 1977 the crater of Mount Nyiragongo contained an active lava lake and the region experienced respite form eruptions. On the tenth of January disaster struck. It began suddenly and with little warning, involved major crater floor collapse, and culminated in voluminous and fast moving lava flows. (14) The lava flowed down the sides of the volcano at a rate of up to 60 miles per hour (Figure 8), sweeping through villages and killing a minimum of seventy people, but some reports quote up to several thousand people. No other place on Earth possesses such a steep-sided stratovolcano containing a lava lake with such fluid lava. Nyiragongo's location close to heavily populated areas increases its potential for causing catastrophes. The 1977 eruption raised awareness of the one-of-a-kind dangers posed by Nyiragongo. (2)





2002

Another major eruption of the volcano began on the seventeenth of January, after multiple months of mounting seismic activity. A fissure, stretching 13 km, opened on the southern slope of the volcano, spreading in an hour from 2,800 m to 1,550 m elevation, reaching the borders of Goma (Figure 4). Lava poured out of three spatter cones at the tip of the fissure and flowed in a river 200 to 1,000 m wide and up to 2 m deep through Goma. Warnings had been given and 400,000 people were evacuated. Lava covered the northern end of the runway of Goma's airport and stretched to Lake Kivu. This concerned authorities who feared the lava might cause the gas-saturated waters beneath the lake to suddenly rise to the surface. (2) About 45 people died in the eruption from asphyxiation by CO2 and buildings collapsing due to the lava and earthquakes. A minimum of 15% of Goma 4,500 buildings were destroyed (Figure 10), leaving approximately 120,000 people with no home (Figure 9). Immediately after the eruption ceased, many
Figure 9 - A child walks near the lava flow. (16)
Figure 9 - A child walks near the lava flow. (16)
earthquakes were felt around Goma and neighboring communities. This swarm activity
Figure 10 - More devastation caused by the 2002 explosion. (17)
Figure 10 - More devastation caused by the 2002 explosion. (17)
continued for about three months and caused the collapse of even more buildings. (15)
Volcanic activity at Nyiragongo is constant, but is confined to the crater, where another lava lake has formed about 250 meters below the level of the 1994 lava lake. (2)






Conclusion


Mount Nyiragongo is a highly active volcano located in Central Africa. This unstable volcano has been the cause of many deaths and may cause many more in the future, unless a way to mitigate another disaster is found. One possibility is through measuring the level of the lava lake. Hopefully with the help of volcanologists from around the world another disaster may be prevented in this underdeveloped region.

References


(1) http://www.volcano.si.edu/world/volcano.cfm?vnum=0203-03=**
(2) http://www.answers.com/topic/mount-nyiragongo
(3) http://www.geology.sdsu.edu/how_volcanoes_work/stratovolc_page.html
(4) http://www.nationmaster.com/encyclopedia/Mount-Nyiragongo
(5) http://www.answers.com/topic/mafic
(6) http://www.vulkaner.no/v/volcan/virunga/nyiragon_e.html
(7) http://www.tboeckel.de/EFSF/efsf_wv/nyiragongo/nyra_e.htm
(8) http://members.tripod.com/Midju/glossary.html
(9) http://www.thefreedictionary.com/basaltic
(10) Lockwood, J. and Casadevall, T., 1994, Active volcanoes and associated hazards in the Goma area, eastern Zaire: Hawaii Center for Volcanology Newsletter, v. 2, no. 1.
(11) http://news.bbc.co.uk/olmedia/1770000/images/_1773206_nyiragongo3_300inf.gif
(12) http://articles.latimes.com/2008/may/23/world/fg-lake23
(13) http://www.pbs.org/wgbh/nova/volcanocity/anat-nf.html
(14) http://www.vulkaner.no/v/volcan/virunga/nyira-bkgnd.html
(15) http://www.volcano.si.edu/volcanoes/region02/africa_c/nyiragon/02nyi03f.jpg
(16) http://graphics8.nytimes.com/images/2002/01/18/international/18WIRE-VOLC.jpg
(17) http://www.dissentmagazine.org/files/Goma%20Volcano%206.jpg
(18) http://www.eri.u-tokyo.ac.jp/KAZANKYO/n_report/72.pdf