Mount Nyiragongo is an active stratovolcano with an elevation of 3470 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 20 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 metres 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. A recent very low elevation of the lava lake was recorded at about 2,700 m.
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. This is because of the extremely low silica content. Hawaiian volcanic eruptions
are also characterized 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 Hawaiian flows to walking pace.
The lava lake activity continued through 2010. At present, the lake is mostly confined within
a broad, steep-sided cinder cone on the crater floor, roughly 60 feet high by 600 feet wide.
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. The hazards posed by eruptions
like this are unique to Nyiragongo. Nowhere else in the world does such a steep-sided
stratovolcano contain a lake of such fluid lava. 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 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 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. A 13 km fissure opened in the south flank of the volcano, spreading
in a few hours from 2800 m to 1550 m elevation, 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 1000 m wide and up to
2 m 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 147 people died in the eruption from asphyxiation by carbon dioxide and buildings
collapsing due to the lava and earthquakes. At least 15% of Goma comprising 4,500 buildings
were destroyed, leaving about 120,000 people homeless. The eruption was the most destructive
effusive eruption in modern history. 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. 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.
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 in relatively high levels, without the dispersing effects of wind, its
effects can be deadly. See also
List of volcanoes in the Democratic Republic of the Congo
List of volcanic eruptions by death toll References
Notes
Bibliography
External links