The Volcano Adventure Guide: Excellent information and background for anyone wishing to visit active volcanoes safely and enjoyably. The book presents guidelines to visiting 42 different volcanoes around the world.
Adapted from: Simpkin and Siebert, 1994, Volcanoes of the World: 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.
Map of East Africa showing some of the historically active volcanoes (red triangles) and the Afar Triangle (shaded, center) -- a so-called triple junction (or triple point), where three plates are pulling away from one another: the Arabian Plate, and the two parts of the African Plate (the Nubian and the Somalian) splitting along the East African Rift Zone.
From: Kious and Tilling, 1996, This Dynamic Earth: The Story of Plate Tectonics: USGS Online version 1.08
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 centre 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.
Intraplate volcanism: A third tectonic setting where volcanism occurs is believed to be the result of mantle plumes and not directly related to plate boundaries. So called hot spot volcanoes fall into this category.
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