Geology of Kenya in brief
Kenya, like all its East African neighbors, lies on one of the great fractures in the earth's crust. The slow ballet of tectonic plates on the Earth's surface produces zones of friction, the preferred sites of intense seismic activity. These numerous earthquakes generate faults. There are three types of fault: reverse faults (or thrust faults), which create mountain ranges; horizontal faults (or strike-slip faults), which displace existing reliefs; and, finally, so-called normal faults, which create collapse trenches also known as rifts.
Kenya's spectacular relief is the result of its specific location at the heart of tectonic activity: the country lies on the meeting line between the African plate and the so-called Somali plate, which covers the western Indian Ocean. The fissure zone between these two plates forms a major rift, the Rift Valley, an endoreic zone. In addition to the latter, which stretches over 6,500 km between the Red Sea in the north and Mozambique in the south, repeated tectonic movements have been the source of a rugged relief and significant volcanism.
The formation of the country's eastern highlands, where the capital, Nairobi, is located, and the western highlands, which slope down towards Lake Victoria, originated from plate impacts, which triggered lava flows (mainly basalt). These gradually formed vast plateaus, dominated by vertiginous escarpments. Numerous volcanic cones were built and are still visible today: Mount Elgon, Menengai, Longonot and Mount Kenya.
The bottom of the Rift is a zone of plateaus, rising from Lake Turkana (250 km long and 40 km wide in the north, to the Ethiopian border) to Lake Naivasha (central region), via Lakes Bogoria, Baringo, Nakuru and Elementaita, before descending to Lakes Magadi and Natron, on the Tanzanian border. Recent volcanoes have appeared here (Suswa, Longonot, Menengai).
It is this geomorphological history that has shaped Kenya's current topography and, indirectly, its climate. Relief has a considerable influence on rainfall. This largely explains why this region, located in the heart of the tropics, is less warm, drier and therefore less forested than other regions at similar latitudes, notably in West Africa.
A divisive rift
What if Africa was splitting in two? That's what was mooted in 2018, when an impressive fault 20 km long, up to 20 meters wide and 50 meters deep appeared in Mai Mahiu, southwest Kenya. The sudden appearance of this continental wound divided the scientific community. Some suggested that it was the beginning of the continent's separation. Wasn't Africa in the process of splitting, between the Nubian Plate and the Somali Plate to the east of the continent? This immediate interpretation is quickly swept aside. The fault is not tectonic in origin and has nothing to do with the East African Fault. Rather, it is a subsidence of soil eroded by heavy rains, in a context of numerous seismic tremors and landslides. Nevertheless, geologists the world over are keeping a close eye on volcanic activity in the region, as the African tectonic plate in the Great Rift Valley inexorably continues to separate from the Somali plate. A geological phenomenon that stretches from the Red Sea to the Zambezi, over 6,000 km and 40 to 60 km wide. In 50 million years' time, the Kenyan Great Rift Valley could become a vast ocean.
Geographic clusters
There are five main geographical zones in Kenya. Each with its own landscape, vegetation and climate: the coastal belt, the central highlands bisected by the Rift Valley, the west and, finally, the north and east of the country.
The coastal belt. Between Somalia and Tanzania, some 500 km of sandy beaches are protected by coral reefs. In the far north, a string of islands fringes the coast, the main ones being Manda, Pate and Lamu. The coastal plain, interrupted by the estuaries of the Tana (the country's main river) and the Galana, is a fairly fertile area, overlooked by the central plateau, which rises rapidly, giving way to desert and wooded savannah.
The inhabitants, mostly Swahili, grow cassava, bananas, sisal, sugar cane, coconuts and fruit trees. This narrow strip of land enjoys a relatively warm and humid climate, far from a true equatorial climate, since rainfall (concentrated between March and May) rarely exceeds 1,000 mm per year. The warmth mitigated by the Indian Ocean trade winds ensures that the coastal belt enjoys pleasant temperatures all year round.
The central highlands. These lie on either side of the Great Rift Valley. This is a very mountainous region that includes Mount Kenya (5,199 m), the Aberdares massif (4,000 m), the Mau escarpment (3,100 m) and the Cherangana Hills (3,500 m) on the western side. The highlands benefit from high rainfall and are intensively farmed by the Kikuyu, Meru and Embu peoples. They enjoy a subtropical, high-altitude climate, characterized by two distinct rainy seasons (November and May to August) and pleasant, sometimes even cool temperatures at higher altitudes (around 0°C at 3,000 m in the evening).
The Rift Valley. The Rift Valley, an immense trench at the junction of the African and Somali tectonic plates, stretching from the Red Sea to the Zambezi, passes through Kenya's highlands and runs the length of the country, from Lake Magadi in the south to Lake Turkana in the north. The bottom of this vast depression is occupied by a series of shallow lakes that attract hundreds of species of birds and offer an ornithological spectacle unique in the world.
Volcanic activity, still latent (numerous geysers and hot springs), has covered the ground with soda-rich volcanic ash, which has gradually been washed into some of the lakes. Lakes Magadi, Bogoria, Elmenteita, Nakuru and Turkana, for example, have particularly alkaline waters, favoring the development of algae on which thousands of pink flamingos feed. Lakes Baringo and Naïvasha, on the other hand, have cool water and are therefore rich in fish. The Rift Valley, too sheltered and below the relief, suffers from a foehn effect: the dry seasons are more marked and rainfall (November, April to May) lower. This explains the semi-desert, even desert-like character of the southern and northernmost areas, home to semi-nomadic, pastoral peoples such as the Turkana.
The West. This region consists of an undulating plateau that stretches along the border with Uganda (interrupted only by the enormous mass of Mount Elgon, 4,321 m) and ends on the shores of Lake Victoria. Home to the Luo people (Kenya's third largest ethnic group), this region is well irrigated and highly fertile, with intensive farming (tea, sugar cane, etc.). Lake Victoria enters through the Kano Fault over a depth of 80 km, forming the Gulf of Winam, at the bottom of which lies the town of Kisumu. The southern part towards Tanzania suffers regular droughts, and the green hills give way to savannah. The western plateau is hot and humid. It reaps the benefits of the Congo's humid equatorial westerly flow, the presence of Lake Victoria's enormous body of water and altitude. This makes it the region with the highest rainfall (over 1,000 mm per year everywhere) and the most regular (it rains throughout the year, most often in the evening). The west is home to tea, coffee and horticulture.
North and east. Northern Kenya is occupied by vast, arid inland plains. Their monotony is broken by Lake Turkana (6,405 km²), north of the Rift Valley, and by numerous volcanic cones. Only the Marsabit massif enjoys significant humidity. The south-eastern part of the country consists of a dry, thankless plateau that drops from 1,300 m to 300 m and extends south-eastwards to the coastal plain. It is dotted with inselbergs (isolated hills in the middle of plains), including the astonishing Taïta Hills (2,208 m) and Chyulu Hills. These two regions cover almost two-thirds of the country, alternating between bush and desert (the Chalbi Desert in the far north is Kenya's most arid zone). Only a few species, such as camels and goats, can be raised here. In fact, this area suffers from subsidence and wind divergence phenomena that limit rainfall (no more than 250 mm or 300 mm per year). Rainfall is therefore rare but very violent (November is the wettest month). After a heavy storm, the many luggas (dry river beds) turn into veritable torrents of mud and sand. The tribes living in these regions (the Samburu, Turkana, Rendille, Gabbra, El Molo and Boran) are mostly nomadic pastoralists. Their limited contact with the modern world has enabled them to preserve much of their age-old traditions and way of life.
A grandiose and varied nature
Kenya offers just about every kind of landscape you'd expect from an African country: savannahs, equatorial forests, high plateaus, deserts and semi-deserts, immense sandy beaches with turquoise waters, coconut groves... From the mountains to the immense Rift Valley depression, from the charismatic silhouette of Kilimanjaro to the Indian Ocean coastline, travellers will be fascinated by a host of grandiose and striking landscapes. With a relatively low density of human settlement and a rich, diverse and surprising wildlife, Kenya is definitely a destination for lovers of the great outdoors. We've mentioned the relief, but the colors and light are just as astonishing, as is the flora, which varies greatly from one region to another.
