East Africa, also known as Eastern Africa or the East of Africa, is a region at the eastern edge of the African continent. It is distinguished by its unique geographical, historical, and cultural landscape.
East Africa is the most topographically diverse region on the African continent. Much of the East African landscape is defined by the Great Rift Valley, which runs from Ethiopia down to Mozambique. The valley was created by the movement of two fault lines in the earth, creating mountains, valleys and lakes throughout this area.
Schematic cross section of the Great Rift Valley.
The Great Rift Valley provides evidence of a split in the African Plate, dividing it into two smaller tectonic plates: the Somalian Plate and the Nubian Plate. Likewise, the Great Rift Valley in East Africa is divided into the Western Rift and the Eastern Rift.
A series of deepwater lakes run along its valley. On the western edge of the Western Rift are the highlands with high-elevation mountain ranges, including the Rwenzori Mountains, the highest in the series. The Virunga Mountains on the Congo-Uganda border are home to endangered mountain gorillas. The Western Rift includes a series of deepwater lakes, such as Lake Tanganyika, Lake Edward, and Lake Albert.
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The eastern edge of the Eastern Rift is home to the inactive volcanic peaks of Mt. Kilimanjaro and Mt. Kenya.
East African mountains, mountain region of Kenya, Tanzania, Uganda, the Democratic Republic of the Congo, Rwanda, and Burundi. The mountains are intimately related to the East African Rift System, the fractures of which extend discontinuously between the Zambezi River valley and the Red Sea and are flanked in many areas by highlands.
Of the major mountains, all but one group-the Ruwenzori (Rwenzori) Range-are of volcanic origin. Rising magnificently from the surrounding plateaus to elevations over 16,000 feet (4,900 metres), the highest peaks, despite their proximity to the Equator, are ice-capped.
Mount Kenya, the Aberdare Range, and the Mau Escarpment are located wholly within Kenya to the north of Nairobi; Mount Elgon lies astride the Uganda-Kenya border; Kilimanjaro extends along Tanzania’s northern boundary with Kenya; and Mount Meru is in northern Tanzania. The Ruwenzori Range stretches between Lakes Edward and Albert on the Uganda-Congo border, and farther south the Virunga Mountains extend along the contiguous borders of Uganda, Rwanda, and Congo.
Physical Features
Physiography
The Aberdare Range, of which the highest peak is Mount Lesatima (Satima), reaching a height of 13,120 feet, and the Mau Escarpment rise steeply from the eastern portion of the Eastern (Great) Rift Valley. To the west, beyond the Uasin Gishu Plateau, Mount Elgon emerges gently from a level of about 6,200 feet; but the spectacular cliffs of its western face dominate the lower plains of eastern Uganda, which lie at about 3,600 feet. The rim of Elgon’s caldera is approximately 5 miles (8 km) in diameter and contains several peaks, of which Wagagai, at 14,178 feet, is the highest.
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The Nyeri-Nanyuki corridor separates the Aberdare Range from Mount Kenya. The second highest mountain in Africa, Mount Kenya has a girth of about 95 miles at 8,000 feet, from which it rises boldly to its restricted summit zone. The craggy twin peaks of Batian (17,057 feet) and Nelion (17,022 feet) are closely followed in height by Lenana (16,355 feet).
Set amid low plateaus, Kilimanjaro is the highest mountain in Africa, rising to 19,340 feet (5,895 metres) at Uhuru peak on the Kibo cone. The generally smooth outlines of the cratered dome of Kibo are in marked contrast to the jagged form of Mawensi, or Mawenzi (17,564 feet); the two summits are connected by a saddle that lies at about 14,500 feet.
The Ruwenzori Range runs parallel to the Western Rift Valley, to which it drops steeply. The fall to the uplands of western Uganda, however, is more gradual. At its base the range is some 80 miles long, and its greatest width is about 30 miles. The summit zone contains six distinct mountain massifs, which are separated by well-defined passes and deep river valleys.
Mounts Baker and Gessi lie entirely within Uganda, while Mounts Stanley, Speke, Emin, and Luigi di Savoia form part of the Uganda-Congo frontier. Of the 10 peaks with heights of more than 16,000 feet, all but one are on Mount Stanley, which includes the highest peak, Margherita, at 16,795 feet.
The Virunga Mountains and their associated lava flows extend across the Western Rift Valley. In the west, Nyamulagira, Nyiragongo, and Mikeno are in Congo; Karisimbi-at 14,787 feet the highest of the Virunga volcanoes-and Visoke are centrally placed on the Congo-Rwanda frontier; and farther east Sabinio (Sabinyo), Mgahinga (Gahinga), and Muhavura, also known as the Mufumbiro Mountains, are on the Rwanda-Uganda frontier. Not all the cones culminate in craters, but several have crater lakes.
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Glaciation
The relict glaciers that occur in the summit zones of Kilimanjaro, Mount Kenya, and the Ruwenzori have little erosive force. Their more powerful predecessors, however, extended down to altitudes between 12,000 and 10,000 feet and even lower and produced arêtes (sharp-edged ridges), cirques (glacial amphitheatres), rock tarns (rock basin lakes), U-shaped valleys, and moraines (boulders and other debris deposited by glacial action).
Early glaciation also affected both Mount Elgon and the Aberdare Range.
More than 30 small glaciers on the Ruwenzori together cover a surface of approximately 1.5 square miles (4 square km), most of which is on Mounts Stanley and Speke; the lowest valley glacier descends to about 14,000 feet. Of the glaciers remaining on Mount Kenya and covering less than 0.3 square mile, the largest are Lewis and Tyndall; the lowest tongue of ice reaches down to about 15,000 feet.
On Kilimanjaro, Kibo crater is strewn with giant blocks of ice, and the outer rims are covered with ice reaching down to about 16,000 feet on the wet southwestern moorlands.
The 20th century was marked in East Africa by a process of glacial retreat that has been rapid but neither constant nor continuous.
Geology
The peneplain of eastern Africa, dating from the Miocene Epoch (about 23 to 5.3 million years ago), has been subject to a general elevational movement. The shoulders of the rift valleys have risen intermittently to produce highlands on which lavas that have been ejected from fissures in the Earth’s surface have in some instances added considerable height.
The most dramatic uplift is that of the Ruwenzori, the only East African mountains that are not volcanic. The ancient plateau surface of gneisses and schists was upfaulted on the west and upwarped on the east. Movements along the faults continue, and the Ruwenzori system is an important earthquake epicentre.
Kilimanjaro is a volcano of complex structure and alkaline lavas situated at an intersection of fault lines. Shira was the first volcano of the group to become inactive, followed in turn by Mawensi and Kibo. The latter retains its caldera-1.5 miles in diameter and 600 feet deep-within which there are found successive inner cones and craters as well as fumaroles (holes or vents that emit gases).
The long-extinct volcano of Mount Kenya has been much denuded, and the highest peaks consist of the crystalline nepheline-syenite (a granular rock of alkalic feldspar, nepheline, and other minerals), which plugged the former vent. Around this core are gently dipping lavas, agglomerates, and tuffs.
Mount Elgon is part of the Eastern Volcanics in Uganda, which consist of soda-rich lavas and associated fragmental tuffs and agglomerates. The Western Volcanics are represented by the Virunga Mountains, of which Nyamulagira and Nyiragongo have remained active into the 21st century. Major eruptions occurred in 1912, 1938, 1948, the 1970s, and 2002. On several occasions a lava stream reached the shores of Lake Kivu. The 2002 Nyiragongo eruption destroyed much of Goma, Congo.
Climate
East Africa has a diverse climate that consists of hot, dry desert regions, cooler regions, and highlands. Its climate generally is rather atypical of equatorial regions, being mostly arid or semi-arid with rainfall totals across much of the lowland regions below 600 millimetres or 24 inches per year.
In fact, on the northern coast of Somalia, annual rainfall is less than 100 millimetres or 4 inches and many years can go by without any rain whatsoever. The causes of the low rainfall totals are not fully understood.
Rainfall generally increases towards the south and with altitude, being around 400 mm (16 in) at Mogadishu and 1,200 mm (47 in) at Mombasa on the coast, whilst inland it increases from around 130 mm (5 in) at Garoowe to over 1,100 mm (43 in) at Moshi near Kilimanjaro.
Rainfall in most of East Africa east of the Rwenzoris and Ethiopian Highlands is characterised by two main rainfall seasons, the long rains from March to May and the short rains from October to December. This is usually attributed to the passage of the Intertropical Convergence Zone across the region in those months, but it may also be analogous to the autumn monsoon rains of parts of Sri Lanka, Vietnam, and the Brazilian Nordeste.
West of the mountains, the rainfall pattern is more typically tropical, with rain throughout the year near the equator and a single wet season in most of the Ethiopian Highlands from June to September - contracting to July and August around Asmara. Annual rainfall here ranges from over 1,600 mm (63 in) on the western slopes to around 1,250 mm (49 in) at Addis Ababa and 550 mm (22 in) at Asmara.
Rainfall variability is influenced by both El Niño events and a positive Indian Ocean Dipole. El Niño events tend to increase rainfall except in the northern and western parts of the Ethiopian and Eritrean highlands, where they produce drought and poor Nile floods. Similarly, a positive Indian Ocean Dipole result in warm sea-surface temperatures off the coast of East Africa and lead to increased rainfall over East Africa.
Temperatures in East Africa, except on the hot and generally humid coastal belt, are moderate, with maxima of around 25 °C (77 °F) and minima of 15 °C (59 °F) at an altitude of 1,500 metres (4,921 ft).
Glaciers in East Africa
Most people do not associate Africa with cryosphere regions, yet the East African Highlands may have contained glaciers since the last glacier maximum 11,000 years ago. Seasonal cryosphere, in the form of snow, exists on the highest peaks of East Africa as well as in the Drakensburg Range of South Africa, the Lesotho Mountains, and the Atlas Mountains in Morocco.
The only existing African glaciers today are on Mt. Kilimanjaro, Mt. Kenya, and three glacier systems in the Rwenzori (“Mountains of the Moon”) between Uganda and the Democratic Republic of Congo. These glaciers likely covered around 25 km2 in total in the early 1900s; today they cover well under 4 km2, based on the most recent surveys (tracking of the Rwenzori is especially difficult, even by satellite).
The Rwenzori in 1906 contained 43 named glaciers, distributed across six peaks and estimated to be half of the glacial area in East Africa at the time. At its maximum during the last glacial period, the Kilimanjaro ice sheet covered over 400 km2. By 1912, when reliable observations began, Kilimanjaro’s glacier extent was 11.4 km2. It had diminished to 1.8 km2 in 2011, losing nearly 90 percent of its extent over 100 years; this includes nearly 30 percent loss of the ice extent that was present in 2000.
The latest estimates of Rwenzori are under 2 km2, and Mt. Kenya has retreated to about 0.1 km2. These glaciers therefore are among the most rapidly receding in the world, losing between 80-90 percent of their surface area since observations began in the late 1800s.
The connection between the retreat of these glaciers and anthropogenic climate change is very complex, as is the climate of East Africa generally. Influences on the region arise from processes ranging from the Indian Ocean and seasonal monsoon (itself tied to El Nino) to winds off the Sahara and even from Antarctica.
Extensive research on Kilimanjaro indicates that a variety of factors, including changes in precipitation patterns and dryness in the region, seem the greatest factors contributing to glacial melt there over the past few decades. The role of temperature remains an area of active debate among tropical glaciologists, with different processes potentially contributing more or less to the different glaciers, and Kilimanjaro being perhaps an especially unique case.
Although the processes causing these shifts remain an area of debate, tropical glaciologists do broadly agree that climate change has impacted the rate of observed glacial loss in East Africa in the past few decades.
Summit ice cover on Kilimanjaro decreased by about one percent per year from 1912-1953, but had risen to 2.5 percent per year from 1989-2007.
Ice core studies on Kilimanjaro show clear evidence of surface glacier melt only in the upper 65 cm of the 49-meter core that spans around 11,000 years. This may indicate that the climate conditions driving the loss of Kilimanjaro’s ice fields are relatively recent.
Glacier and snow melt form a very small portion of water resources in this region, with recent measurements showing them contributing at 2 percent or less. The rain forests along the sides of these peaks, and rainfall at those altitudes play the greatest role in East African water resource systems.
Whether the total loss of glaciers in the region will have any impact on these rainfall patterns at the forest level, while unlikely, remains open to debate.
Africa's last glaciers set to vanish by 2050 predicts new UNESCO report • FRANCE 24 English
Ecoregions and Conservation
The ecoregion encompasses moderate to high altitude habitats along a chain of isolated mountains flanking the Rift Valley. The northern extent is at Mount Kinyeti in southern Sudan, through to Mount Moroto and Mount Elgon in Uganda, and the Aberdare Range to Mount Kenya in Kenya. Further south, the ecoregion includes the forests of the Nguruman Scarp in southern Kenya and Mount Kilimanjaro in northern Tanzania. The ecoregion occupies elevations above c. 1,500 m altitude, with the highest altitudes of some mountains separated into the East African montane moorlands ecoregion.
The climate is temperate and seasonal, with night temperatures falling below 10°C in the cold season and rising to above 30°C during the day in the warm season. At the higher elevations frosts are possible. Rainfall varies between 1,200 and <3,000 mm per annum, with a distinct wet (October-December and March-June) and dry (January-February and July-October) season. The climate of these mountains is wetter than the surrounding lowlands, but has a pronounced rainshadow, with the eastern and southern faces being significantly wetter.
At lower attitude, the submontane and montane forests are dominated by the timber species Ocotea usambarensis, Juniperus procera, Podocarpus falcatus, P. latifolius, Nuxia congesta, and Newtonia buchanii. At higher altitudes the vegetation becomes dominated by the bamboo Arundinarium alpine and trees such as Hagenia abyssinica.
These mountains support a diverse avifauna, including eight endemic bird species. Some of them, such as the Aberdare cisticola, Abbotts starling, and Kenrick’s starling, occur on only two or three mountain ranges within the ecoregion.
The mammal fauna includes eight strictly endemic species of shrews and rodents. Near-endemic mammals include Jackson’s mongoose, Abbot’s duiker, sun squirrel, and the eastern tree hyrax. There is also a number of strictly endemic reptile and amphibian species, such as Tilbury's chameleon, Müller's leaf chameleon, Mount Kenya hornless chameleon, and Ashe’s bush viper.
While there is no endemic large mammals, charismatic representation of Central African species include African golden cat, giant forest hog, African bush elephant, and black rhinoceros.
The relatively low rates of endemism here compared to other tropical forest ecoregions in eastern Africa is likely because the forests are not especially old, most being formed on volcanoes that are 1-2 million years old, some of which are still active or have erupted within the past 10,000 years.
Historically, this ecoregion was a mosaic of forest, bamboo, and grasslands throughout its middle elevations, grading into extensive areas of savannah and woodlands at lower elevations and heathland/moorland habitats at higher elevations. Over time, the level of habitat fragmentation has increased due to human activities.
