Mount Kenya (Kenya, Mount), the Aberdare Range, and the Mau Escarpment are located wholly within Kenya to the north of Nairobi; Mount Elgon (Elgon, Mount) lies astride the Uganda-Kenya border; Kilimanjaro extends along Tanzania's northern boundary with Kenya; and Mount Meru (Meru, Mount) 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.

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.

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. Mount Meru, about 40 miles southwest of Kilimanjaro, attains an altitude of 14,978 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 (Margherita Peak), 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 (Karisimbi, Mount)—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.

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.

The peneplain of eastern Africa, dating from the Miocene Epoch (between 23.8 million and 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 (Kenya, Mount) 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 were active during the 20th century. Major eruptions occurred in 1938 and 1948 and during the 1970s, and on several occasions a lava stream reached the shores of Lake Kivu. In 2002 Nyiragongo erupted again, destroying much of Goma, Congo.

The Virunga Mountains separate the basins of the Nile and the Congo rivers and are the only East African mountains to form a divide of continental stature. The entire system of the Ruwenzori Range drains into the Semliki River, a tributary of the Nile. Because they are relatively young, the mountain systems present good examples of consequent drainage (that is, determined by the initial slope of the land) such as the radial system of Mount Elgon, in which streams radiate from a central area, and the parallel streams of the Aberdare dip slopes. The porous nature of volcanic materials often results in areas devoid of surface drainage.

The succession of soils is from the raw mineral type of the summit area, through the dark peaty loams of the Afro-Alpine zone and the strong brown loams of high organic content in the forest belt, to the ferruginous (iron-bearing) soils of the lower slopes. Volcanic material presents a range from the unaltered rock of the most recent eruptions to the well-developed fertile soils on surfaces that have been exposed for longer periods of time.

In a region of predominantly dry climate, the mountains are conspicuous as areas of high rainfall. Affected by the convergence of Indian Ocean and Atlantic airstreams, the Ruwenzori as a whole comprise the wettest and the cloudiest of the mountains, where moist conditions penetrate up to the peaks and about 80 inches (2,000 mm) of rain annually falls at 15,000 feet. Kilimanjaro, Mount Kenya, and Mount Elgon are affected by their position in relation to southeasterly and northeasterly airstreams. Below 10,000 feet they are wettest on their southeastern and southern sides, with annual total precipitation rising to 100 inches on Mount Kenya; they are driest on their northern flanks, with less than 40 inches of rainfall yearly. Rainfall decreases above a cloud ceiling at about 10,000 feet, especially on Kilimanjaro, where the Afro-Alpine zone is a veritable desert. On the western and southwestern slopes the diverted southeast trade winds are sucked up each of the mountains as westerlies, creating an increase of cloud and precipitation. At the summit of Mount Kenya, temperatures seldom rise above the freezing point, and above 14,500 feet precipitation occurs mainly in the form of snow.

Vegetation in the East African mountains often occurs in a succession of altitudinal zones. This succession is well developed on Mount Kenya, where it emerges from the surrounding savanna (grassland with scattered bushes or trees) and begins on the lower slopes with a crescent of cultivated land. The montane forest extends upward from a lower limit of about 6,000 feet to 10,000 feet and includes giant trees, such as camphor and various figs, cedar, yellowwood, and the East African olive. From about 8,000 feet the forest consists of montane bamboo, and at its upper limit parkland and low thicket fringe the succeeding zone of giant heather. At 11,000 to 12,000 feet the heather zone gives way to the Afro-Alpine zone in which tree groundsel and the giant lobelia rise out of a ground vegetation of tussocky grassland and everlastings (composite plants, the flowers of which can be dried without loss of colour or form). Mosses and lichens survive up to about 15,000 feet, but bare rock and ice are exposed above that height.

The montane forest of Kilimanjaro is drier than that of Mount Kenya. Bamboo is virtually absent, although it is abundant on neighbouring Mount Meru, and there is no parkland zone. The heather zone is strongly represented, whereas the Alpine semidesert is poor in flowering plants. Mount Elgon reaches into the Afro-Alpine zone, as do the summits of the Aberdare Range. On the northwest of the Ruwenzori, the lower slopes touch upon the equatorial forest, and the vegetation is moister and more luxuriant than that of the eastern mountains. Above the bamboo forest and the wooded parkland, the Virunga Mountains extend into the heather zone and, in the three highest volcanoes, into the Afro-Alpine zone.

The Afro-Alpine vegetation of the East African mountains is unique. With the increase of temperatures in post-Pleistocene times (since about 10,000 years ago), the cold-loving plants retreated to the mountains, where they have been preserved and somewhat transformed. Despite the enormous distances that separate the mountains, plants in the respective Afro-Alpine zones are closely comparable. There are lobelia and Alchemilla (lady's mantle) species common to all the mountains, although the tree groundsel species are limited within neighbouring mountains. The phenomenon of giantism is common, while dwarfism occurs at the highest altitudes.

Elephants, rhinoceroses, buffalo, antelope, hyrax, bush pigs, and monkeys, including the black-and-white colobus, are among the main inhabitants of the montane forest. The bongo (forest antelope) and the giant forest hog have not been observed on Kilimanjaro, perhaps because of its lack of bamboo forest and its isolation from the mountains to the north. Mountain gorillas and golden monkeys live in the Virunga Mountains, and chimpanzees in the Ruwenzori Range. Trout have been introduced into the streams of the more accessible mountains.

Mammals of the upper forests, including the leopard and antelope such as the duiker and the eland, penetrate into the moorland and Afro-Alpine zones, where the hyrax and the groove-toothed rat are the most obvious inhabitants. Birds include the lammergeier (one of the largest birds of prey, resembling the eagle and vulture), the mountain chat (a songbird), and the scarlet-tufted malachite sunbird (a small, brilliantly coloured songbird). Animal life, like the vegetation, shows resemblances that suggest a retreat of its distribution from the surrounding plateaus to the montane islands of refuge.

Population is confined to the lower slopes, with the upper limit of settlement at about 7,000 feet. Bananas and millet are common subsistence crops, and coffee is an important cash crop. On the southern and eastern slopes of Kilimanjaro the Chaga (Chagga) have long used an effective system of irrigation based on the ridge-and-valley relief of the mountain. High population densities among the Chaga are matched by those among the Kikuyu and related groups on the slopes of the Aberdare Range and around the southern and eastern margins of Mount Kenya. The Gisu have densely settled the western slopes of Mount Elgon below the forest zone.

Population density is high on either side of the northern nose of the Ruwenzori; the Konjo hillmen live mainly on the eastern flank of the range. The Pygmy Twa occupy the forests of the Virunga Mountains, the lower slopes of which are cultivated by the far more numerous Hutu.

Copper ore was formerly mined at Kilembe, Uganda, on the southeastern flank of the Ruwenzori. Other mineral resources include tin deposits also southeast of the Ruwenzori, tungsten deposits in the Virunga Mountains in Uganda, and diatomite in the Aberdare Range.

The closed forests are mainly under forest reserve and are classed as presently productive of timber. The most important output of sawn wood has come from the more accessible mountains of Kenya and Tanzania, where cedar, podo (or yellowwood), and camphorwood are among the principal timbers; the quantities produced, however, are small. Land cleared for cultivation in the lower part of the forests forms rich agricultural zones in which a considerable variety of crops—including coffee, tea, wheat, pyrethrum (a chrysanthemum used in the production of insecticides), bananas, millet, root crops, and vegetables—may be grown. Cattle are raised on the northern slopes of Mounts Kenya and Elgon and on Kilimanjaro. The narrow agricultural belt could be widened, and there has been a tendency for the extension of cultivation into lower altitudes by the use of irrigation.

The mountains are an important tourist attraction. Kilimanjaro National Park covers the mountain from 6,000 feet to the summit, and other parks include Mount Kenya above 10,200 feet, the moorland zone of the Aberdares, and a sector of the Kenya portion of Mount Elgon. In the Uganda section of the Virunga Mountains, the Kigezi Gorilla Game Reserve is situated on the northern slopes of Mounts Muhavura and Mgahinga (Gahinga). In the Rwanda and Congo (Kinshasa) portions of the Virunga Mountains, gorillas are protected, respectively, in the Volcanoes National Park and the Virunga National Park.

The Ruwenzori form a barrier to east-west transport, and road connections between Uganda and Congo pass south of the range. The Mau Escarpment and the Aberdare Range deflect the main roads to their northern and southern flanks, but each is crossed by a secondary road. The Nyeri col between the Aberdares and Mount Kenya is used as a gateway to the north. There are circular routes around Mounts Kenya and Elgon, and the bases of all the mountains are reasonably accessible.

In 1848 the snow-covered summit of Kilimanjaro was observed by the German missionary Johannes Rebmann (Rebmann, Johannes), and the following year Johann L. Krapf obtained a view of the snows of Mount Kenya. In 1888 the Welsh explorer Henry Morton Stanley glimpsed the Ruwenzori through a break in their cloud cover and equated them with the Mountains of the Moon of Ptolemy.

A number of expeditions on Kilimanjaro preceded that of 1889, in which the German geographer Hans Meyer conquered the summit of Kibo. Partial ascents of Mount Kenya were made before the British geographer Halford John Mackinder reached the summit of Batian in 1899. The Ruwenzori awaited the expedition of Luigi, Duke dʿAbruzzi, in 1906 for the conquest of their major peaks, and in 1907–08 Adolf Friedrich, Duke of Mecklenburg, made a comprehensive survey of the Virunga Mountains. The southern side of Elgon was visited in 1883 and the caldera was traversed in 1890; in 1911 Wagagai was climbed. In 1932 a Belgian scientific mission explored the western slopes of the Ruwenzori, climbing several peaks.

Since 1931, aerial photography has assisted in the production of excellent maps of the major mountains and their glaciers. Under the stimulus of the International Geophysical Year of 1957–58, glaciological expeditions were mounted on the Ruwenzori, Mount Kenya, and Kilimanjaro.

Kilimanjaro, Kenya, and Ruwenzori are names of African origin; the first two are of somewhat uncertain meaning, and Ruwenzori may come from Nyoro words meaning “place of rain.” Elgonyi was the Masai name for Elgon, but the Gisu name Masaba remains current in the Bantu languages. The names Kibo and Mawensi are of African derivation, and the highest peaks of Mount Kenya were named for Masai chiefs. With one exception, Ensonga, the major mountains and peaks of the Ruwenzori have European names, while Virunga nomenclature is African.