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Africa Volcanoes and Volcanics

Africa is the only region other than the Mediterranean with an historically dated B.C. eruption (at Mount Cameroon, observed by a passing Carthaginian navigator in the 5th century B.C.). By the 15th centuray A.D., however, when Portuguese exploration of Africa had begun and Vasco de Gama sailed to India via the Cape of Good Hope, only 2 more eruptions had been recorded, both from Ethiopia. In the next 3 and two-thirds centuries, another 20 some eruptions were recorded, but the main historical record of the continent began with the opening of the Suez Canal at the end of 1869, and the heyday of African exploration that followed.

Most African volcanoes result from hotspots, the rifting in East Africa, or a combination of the two. The East African rift, one of the world's most dramatic extensional structures, has produced the continent's highest and lowest volcanoes, ranging from the massive Kilimanjaro to vents in Ethiopia's Danakil Depression that lie below sea level. Two neighboring volcanoes in Zaire's (today's Democratic Republic of the Congo) Virunga National Park, Nyamuragira and Nyiragongo, are responsible for nearly two-fifths of Africa's historical eruptions.

Africa has the highest percentage of volcanoes that are undated but known to be Holocene, reflecting the early stage of detailed geologic studies. The continent has the most volcanic centers with pyroclastic cones and fissure vents (as primary features), many of which lie within the East African Rift. It also has many shields, but the most common edifice type is the stratovolcano. The continent, however, has recorded relatively few large (VEI >/=4) eruptions in the Holocene (and 3 of these 4 were B.C.). Africa leads the world in lava lake production, with 9 percent of its eruptions -- all at Nyiragongo and Erta Ale - having exhibited this uncommon characteristic.

In East Africa, spreading processes have already torn Saudi Arabia away from the rest of the African continent, forming the Red Sea. The actively splitting African Plate and the Arabian Plate meet in what geologists call a triple junction, where the Red Sea meets the Gulf of Aden. A new spreading center may be developing under Africa along the East African Rift Zone. When the continental crust stretches beyond its limits, tension cracks begin to appear on the Earth's surface. Magma rises and squeezes through the widening cracks, sometimes to erupt and form volcanoes. The rising magma, whether or not it erupts, puts more pressure on the crust to produce additional fractures and, ultimately, the rift zone.

East Africa may be the site of the Earth's next major ocean. Plate interactions in the region provide scientists an opportunity to study first hand how the Atlantic may have begun to form about 200 million years ago. Geologists believe that, if spreading continues, the three plates that meet at the edge of the present-day African continent will separate completely, allowing the Indian Ocean to flood the area and making the easternmost corner of Africa (the Horn of Africa) a large island.

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Major Volcanoes of Ethiopia
(currently just Erta Ale)

Erta Ale is an isolated basaltic shield volcano that is the most active volcano in Ethiopia. The broad, 50-kilometer-wide volcano rises more than 600 meters from below sea level in the barren Danakil depression. Erta Ale is the namesake and most prominent feature of the Erta Ale Range. The 613-meter-high volcano contains a 0.7 x 1.6 kilometers, elliptical summit crater housing steep-sided pit craters. Another larger 1.8 x 3.1 kilometer-wide depression elongated parallel to the trend of the Erta Ale range is located to the southeast of the summit and is bounded by curvilinear fault scarps on the southeast side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally oveflowed its rim. The summit caldera is renowned for one, or sometimes two longterm lava lakes that have been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the northern flank of Erta Ale.

Most African volcanoes result from hot spots, rifting in East Africa, or a combination of the two. The East African rift, one of the world's most dramatic extensional structures, has produced the continent's highest and lowest volcanoes, ranging from massive Kilimanjaro to vents in Ethiopia's Danakil Depression that lie below sea level.

Mount Kilimanjaro, Tanzania, the highest [19,340 feet (5895 meters)] and most famous mountain in Africa, is located in Tanzania just adjacent to the Kenya border. Three distinct volcanoes can be seen ... Kibo (center volcano) with the highest peak and a permanent glacier and snow field at its summit; Shira (most westerly), the oldest that has been eroded into a plateau-like feature standing 12 395 feet (3778 meters) above sea level; and Mawenzi (most easterly) with a well-defined peak that reaches 17 564 feet (5354 meters) above sea level. The overlapping lava flows from these three volcanoes have almost obliterated their individual uniqueness into a single complex volcanic feature. The southern flanks of the mountain are more deeply eroded than northern slopes. Perhaps the cloud buildup indicates the increased severity of erosion is caused by more precipitation on the southern slopes than on the northern slopes.

Marion Island, South Africa's only historically active volcano, lies at the southwest end of a submarine plateau immediately south of the southwest Indian Ocean Ridge, opposite Prince Edward Island. The low profile of 24-kilometer-wide Marion Island is formed by two young shield volcanoes that rise above a flat-topped submarine platform. The 1230-meter-high island is dotted by about 150 cinder cones, smaller scoria cones, and coastal tuff cones. More than 130 scoria cones and many lava flows formed during the Holocene. Many of these appear younger than the 4,020 BP peat overlying one of the flows (Verwoerd and others, 1981). Young unvegetated lava flows appear to be only a few 100 years old (Verwoerd and Langenegger, 1967). A meteorological station is maintained there by the South African government.

Indian Ocean Volcanoes and Volcanics Menu

Mount Cameroon
Location: Cameroon, West Africa
Latitude: 4.203 N
Longitude: 9.17 E
Height: 4,095 meters (13,436 feet)
Type: Stratovolcano

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Major Volcanoes of Cameroon, West Africa

Mount Cameroon rises over 4 kilometers (2.5 miles) above the coast of western Cameroon. Its historical activity has consisted of moderate explosive and effusive eruptions from both summit and flank vents. Numerous small cinder cones dot the flanks and surrounding lowlands.

Mount Cameroon, one of Africa's largest volcanoes, rises above the coast of west Cameroon. More than 100 small cinder cones, often fissure-controlled parallel to the long axis of the volcano, occur on the flanks and surrounding lowlands. A large satellitic peak, Etinde, is located on the southwest flank. Historical activity, the most frequent of west African volcanoes, was first observed in the 5th century BC by the Carthaginian navigator Hannon. During historical time, moderate explosive and effusive eruptions have occurred from both summit and flank vents.

An eruption during February-March 1959 produced a large E-flank lava flow. Increased seismicity was recorded in November 1975, but no eruption occurred. The last eruption, October-November 1982, produced lava fountaining from a radial fissure 6.5 kilometers southwest of the summit and a lava flow that moved 12 kilometers down the southwest flank. Two towns were evacuated, and tephra caused damage to plantations. The first seismic network was installed in 1984 by the Ekona Unit for Geophysical and Volcanological Research (ARGV) of the Institute for Mining and Geological Research (IRGM).

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Major Volcanoes of the Democratic Republic of the Congo

Most African volcanoes result from hot spots, rifting in East Africa, or a combination of the two. The East African rift, one of the world's most dramatic extensional structures, has produced the continent's highest and lowest volcanoes, ranging from massive Kilimanjaro to vents in Ethiopia's Danakil Depression that lie below sea level. Two neighboring volcanoes in Zaire's (Webnote: now called Democratic Republic of the Congo) Virunga National Park, Nyamuragira and Nyiragongo, are responsible for nearly two-fifths of Africa's historical eruptions.

Africa's most active volcano, Nyamuragira is a massive basaltic shield volcano that rises north of Lake Kivu across a broad valley northwest of Nyiragongo volcano. The volcano has a volume of 500 cubic kilometers and extensive lava flows from Nyamuragira cover 1500 square kilometers of the East African Rift. The 3058-meter-high summit is truncated by a small 2 x 2.3 kilometer summit caldera that has walls up to about 100 meters high. Historical eruptions have occurred within the summit caldera, frequently modifying the morphology of the caldera floor, as well as from the numerous fissures and cinder cones on the volcano's flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938. Twentieth-century lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

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Major Volcanoes of the Democratic Republic of the Congo

Most African volcanoes result from hot spots, rifting in East Africa, or a combination of the two. The East African rift, one of the world's most dramatic extensional structures, has produced the continent's highest and lowest volcanoes, ranging from massive Kilimanjaro to vents in Ethiopia's Danakil Depression that lie below sea level. Two neighboring volcanoes in Zaire's (Webnote: now called Democratic Republic of the Congo) Virunga National Park, Nyamuragira and Nyiragongo, are responsible for nearly two-fifths of Africa's historical eruptions.

One of Africa's most notable volcanoes, Nyiragongo contained an active lava lake in its deep summit crater that drained in 1977. In contrast to the low profile of its neighboring shield volcano, Nyamuragira, Nyiragongo displays the steep slopes of a stratovolcano. Benches in the steep-walled, 1.2-kilometer-wide summit crater mark former lava lake levels. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a northeast-southwest zone extending as far as Lake Kivu. Many cones are buried by voluminous flank lava flows, the most recent of which extends from an east-flank fissure south to within 4 kilometers of Goma. Monitoring is done from a small observatory building located in Goma, approximately 18 kilometers south of the Nyiragongo crater. A previous lava lake in the deep summit crater of Nyiragongo, first reported by G. A. Von Gotzen on 11 June 1894, drained suddenly through radial fissures on 10 January 1977, killing about 70 people. Lava lake activity resumed in June 1982, but had ceased by early 1983. The lava lake was again activated after an eruption that began in June 1994.

Oku Volcanic Field
Location: Cameroon, West Africa
Latitude: 6.25 N
Longitude: 10.50 E
Height: 3,011 meters (9,879 feet)
Type: Maars
Number of eruptions in the past 200 years: 0
Latest Eruptions: 400 years ago ² ...
Remarks: Location of the August 12, 1986, sudden release of CO2 gas from Lake Nyos in Cameroon resulting in death of at least 1,700 people by asphyxiation².

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Major Volcanoes of Cameroon, West Africa

Numerous maars and basaltic cinder cones lie on or near the deeply dissected Mount Oku massif along the Cameroon volcanic line. Two of these crater lakes, Lake Nyos to the north and Lake Monoun to the south (~100 kilometers ESE of Lake Nyos), have produced catastrophic gas release events. The 15 August 1984 gas release at Lake Monoun that killed 37 people (Sigurdsson and others, 1987) was attributed to overturn of stratified lake water, triggered by an earthquake and landslide. The Lake Nyos event on 21 August 1986 caused at least 1,700 fatalities. The emission of around 1 cubic kilometer of magmatic CO2 has been attributed to overturn of stratified lake waters as a result of a non-volcanic process, or to phreatic explosions or injection of hot gas into the lake.

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