The Rift Valley, sculptor of volcanoes in the north
East Africa is a vast, high plateau rising some 1,500 metres above a narrow coastal belt. It is dramatically broken by the Great Rift Valley, a 20-million-year-old fissure running from the Dead Sea to Mozambique, which can plunge up to 2,000 m deep across the African continent. The Rift Valley divides Tanzania into two parts. The high mountains are volcanic, created by the emergence of the Rift Valley. Kilimanjaro is the most recent of these volcanoes. Formed around a million years ago, it was still growing 100,000 years ago, but is now dormant. Mount Meru is older. The Ngorongoro crater (2,286 meters) is a collapsed volcano caldera 20 km in diameter and covering almost 300 km2. It was once as high as Kilimanjaro! Today, it's a life-size Noah's Ark, as the crater provides year-round water for the dense fauna that lives there. Tanzania's only active volcano, Ol Doinyo Lengai (3,188 metres), rises from the Rift Valley north of Ngorongoro and is the sacred mountain of the Maasai. To the west of the crater, in the highlands, the Serengeti plains (altitude approx. 1,500 m) stretch endlessly. The Rift Valley also created the Usambara and Pare mountain ranges, between Kilimanjaro and the coast.
The eastern branch of the Rift Valley, (Gregory Rift) in the extension of Lake Turkana (in Kenya), is a fault at the bottom of which lie salt lakes: Lakes Natron, Manyara and Eyasi. This is where the northern national parks are located. These mountain ranges feed a relatively large number of rivers that flow into the Indian Ocean. The Western Rift Valley corresponds to Lake Tanganyika and Lake Nyasa. Lake Tanganyika drains water from the north-western highlands into the Atlantic Ocean. Lake Nyasa drains the waters of the southern highlands, situated at an altitude of around 2,800 meters. Lake Victoria lies on a high plateau between the two branches.
A relief of mountains, high plateaus and plains
The north-east of Tanzania is very mountainous. Most of the region's rivers flow into Lake Victoria, one of the two sources of the Nile. Those in central Tanzania - a large plateau - are drained by rivers that flow into the Indian Ocean. The southern half of this central plateau is grassland in the Miombo Forest ecoregion, most of which is covered by the immense Selous National Park. Further north, the plateau is arable land and includes the country's political capital, Dodoma. To the south-west of the Rufiji River, a stream-covered plateau is divided into several distinct basins. To the east, dense vegetation grows, fed by abundant rainfall. The vegetation becomes sparser the further west you go, giving way to a vast arid region: the Maasai steppe, between lakes Victoria, Tanganyika and Malawi. The country's main rivers from north to south are the Pangani, Wami, Ruvu, Rufiji, Matandu, Mbwemkuru and the Ruvuma, which forms the southern border with Mozambique.
Kilimanjaro, the roof of Africa
Kilimanjaro, the mythical roof of the African continent, is an isolated massif on the Great Rift. Located some 300 km from the equator, entirely in Tanzanian territory, 60 km long from east to west and 40 km wide from north to south, it towers 5,000 metres above the surrounding plains: Maasai steppe, farmland and national parks. This immense volcano, with its distinctive shape, has three distinct peaks. The Kilimanjaro volcano is not extinct, as is often claimed, but merely dormant. The last major eruption was 100,000 years ago. Shira Peak (3,962 metres), to the west, is characterized by its gentle slopes and surrounding plateaus. Mawenzi (5,149 metres), to the east, is a series of narrow, fairly jagged needles, access to which is made difficult by the verticality and nature of the rock. Kibo is the main summit (5,895 metres). A broad plateau reveals several concentric circles, the result of ancient eruptions. At its center is a deep crater (the Reusch crater), which is semi-active: white fumaroles, or at least the smell of sulfur, frequently emanate from it. Snow is less prevalent. Glaciers lie to the north and especially to the south of Kibo. Unfortunately, this is one of the places in the world where global warming is having the greatest impact. In the space of a century, Kili has lost 80% of its ice reserves! Finally, between Kibo and Mawenzi lies the Saddle, a vast arid plateau of stone and ash, stretching to an altitude of around 4,400 metres.
The coastal strip and the Zanzibar archipelago
The coastal strip at sea level, with an average width of 16 km and a length of 800 km, is very wild, lined with beaches and palm trees as far as the eye can see. These beaches are interrupted only by a few river deltas and creeks, including those of the deep-water ports of Tanga, Dar es Salaam and Mtwara. Formed by a coral platform, these plains are mainly occupied by mangrove forests. Unguja, the main island of the Zanzibar archipelago that it forms with the island of Pemba, has a few hills planted with a modest tropical forest and banana plantations in its center, and a few pockets of preserved forest and mangroves, but remains flat and very low to the east and south. It is obviously very fertile, given its centuries-long yield of spices. But it is above all its beaches that have made its reputation. Here, the coral reef forms a protective ring some 1 km long, separating the lagoon with its translucent turquoise waters from the deep, choppy waters of a darker blue. With the two daily tides, the coral and rocks gradually reveal themselves under the sun, forming small pools of water and gradations of color on the palette of blues and greens. This is the real Zanzibar spectacle, as the landscape changes rapidly with the tides.
Lake Victoria, Africa's largest lake in danger
Lake Victoria (or Nyanza in Kiswahili) is the largest freshwater lake in Africa and the second largest in the world, with 68,100 km2- twice the size of Belgium. It stretches over 320 km in length (north to south) and 275 km in width: a sea within a continent! It owes its name to the English explorers Burton and Speke, who discovered it in 1858 and named it in honour of Queen Victoria. Quite shallow, it lies at an altitude of almost 1,100 metres. Bordered by Kenya and Uganda, it forms a triple border. It is the source of the White Nile, the Nile's longest tributary, and formed by a depression between the two branches of the Great Rift Valley formed four million years ago. Lake Victoria is home to the Rubondo Island National Park. The introduction of the Nile perch in the 1950s was an ecological disaster. With its incredible voracity, this fish - which today accounts for 80% of the lake's fish - is responsible for the disappearance of some 200 species. What's more, the lake's water level has fallen significantly, the most in forty years... Illegal fishing is also on the increase, to the point where the Nile perch is over-fished. Another major problem is pollution. The lake is heavily polluted by a multitude of waste products from the densely populated cities that border it, including large quantities of plastic waste and chemical fertilizers. The situation is extremely worrying.
Tanganyika, the second largest lake in Africa with abyssal depths
Also discovered in 1858 by the English explorers Burton and Speke, this lake, 60 km wide on average, is the longest in the world (680 km, giving it a surface area of around 32,000 km2). It is also the second deepest lake in the world (1,435 metres), after Lake Baikal (1,740 metres), with the bottom at 655 metres below sea level and the surface at 770 metres above sea level! It was formed around 20 million years ago by the separation of the continental and eastern plates of Africa, and continues to widen by a few centimetres every year. Real storms occur here from time to time. The surrounding mountains exceed 2,600 metres in altitude. Bujumbura, the capital of Burundi, forms its northern end, the Democratic Republic of Congo its western shore, and Zambia its southern end. Deep-sea fishing is abundant: tilapia, Nile perch, catfish, tigerfish, sangaras and dagaas are frequently eaten fried or dried in the sun and sent in boatloads to the rest of the country. The depth of the lake keeps the water relatively fresh and very healthy.
Lake Nyasa, 3rd largest in Africa, the most mysterious
Nyasa means "Big Water", and this lake is indeed the third largest in Africa. It is 550 km long, 75 km wide and covers an area of 11,400 km2. Its surface area is comparable to that of Belgium. It was discovered by the Portuguese Gaspar Bocarro in 1616. Unlike Lake Victoria, which becomes the Nile and flows into the Mediterranean, and Lake Tanganyika, which flows into the Atlantic Ocean, the waters of Lake Nyasa mix with those of the Zambezi River in Mozambique, which flows into the Indian Ocean. This lake is the southernmost of the Great East African Rift, and its most southerly geological manifestation. The whole mountainous region is superb, as is the view over this long, steep-sided lake of 2,600 km2, dominated to the east by the Livingstone Mountains. The lake itself stands at an altitude of 472 metres, with a depth of over 500 metres, and the surrounding mountain range peaks at almost 3,000 metres. Although only intermittently cloudy, it rains more than 2,000 mm of water per year, as the mountains to the north of the lake (the Poroto mountains with the beautiful Kitulo plateau to the east, the Kipengere and Livingstone mountains) hold back all the clouds brought in by the prevailing south-easterly winds. These clouds originate from the Indian Ocean, and are weighed down on their way by evaporation from the lake.
