Largest Lakes in Tanzania

Hydrology and limnology

Lake Victoria receives 80 percent of its water from direct rainfall. Average evaporation on the lake is between 2.0 and 2.2 metres (6 ft 7 in and 7 ft 3 in) per year, almost double the precipitation of riparian areas. Lake Victoria receives its water additionally from rivers, and thousands of small streams. The Kagera River is the largest river flowing into this lake, with its mouth on the lake's western shore. Lake Victoria is drained solely by the Nile River near Jinja, Uganda, on the lake's northern shore.

In the Kenya sector, the main influent rivers are the Sio, Nzoia, Yala, Nyando, Sondu Miriu, Mogusi, and Migori. The only outflow from Lake Victoria is the Nile River, which exits the lake near Jinja, Uganda.

Geology

Photojournalist John Reader, writing in his Alan Paton Literary Award-winning Africa: A Biography of a Continent, describes Lake Victoria as being relatively geologically young at about 400,000 years old—having been formed as westward-flowing rivers were backed up "when a fractured block of the Earth's crust tilted along the line of the Great Rift Valley, raising its western edge". A primary study, attempting "fluvial differentiation of the basin of Lake Victoria", draws several relevant tentative conclusions.

History and exploration

The first recorded information about Lake Victoria comes from Arab traders plying the inland routes in search of gold, ivory, other precious commodities, and slaves.

Many Africans tribes lived in the catchment area around the lake. It was first sighted by a European in 1858 when the British explorer John Hanning Speke reached its southern shore while on his journey with Richard Francis Burton to explore central Africa and locate the Great Lakes. Believing he had found the source of the Nile on seeing this "vast expanse of open water" for the first time, Speke named the lake after Queen Victoria.

Geography

Lake Tanganyika is an ancient lake, one of only twenty more than a million years old. Its three basins, which in periods with lower water levels were separate lakes, are of different ages. The central lake began to form 9–12 million years ago (Mya), the northern 7–8 Mya and the southern 2–4 Mya.

Today Lake Tanganyika is situated within the Albertine Rift, the western branch of the East African Rift, and is confined by the mountainous walls of the valley. It is the largest rift lake in Africa and the second-largest freshwater lake by volume in the world. It is the deepest lake in Africa and holds the greatest volume of fresh water on the continent, accounting for 16% of the world's available fresh water.

History

It is thought that early Homo sapiens were making an impact on the region during the Stone Age. The time period of the Middle Stone Age to Late Stone Age is described as an age of advanced hunter-gatherers.

In the mid–19th century, Swahili Arab traders from Zanzibar established a caravan route from Bagamoyo via Tabora to Ujiji on Lake Tanganyika. They brought sailing dhows to navigate the lake and traded in slaves, ivory, guns and cotton. Chief among these traders was Tippu Tip in the second half of the 19th century, who established a state west of the lake.

The first known Westerners to find the lake were the British explorers Richard Burton and John Speke, in 1858. They located it while searching for the source of the Nile River.

Geography

Lake Malawi is between 560 kilometres (350 mi) and 580 kilometres (360 mi) long, and about 75 kilometres (47 mi) wide at its widest point. The lake has a total surface area of about 29,600 square kilometres (11,400 sq mi). The lake is 706 m (2,316 ft) at its deepest point, located in a major depression in the north-central part. Another smaller depression in the far north reaches a depth of 528 m (1,732 ft). The southern half of the lake is shallower; less than 400 m (1,300 ft) in the south-central part and less than 200 m (660 ft) in the far south.

The lake has shorelines on western Mozambique, eastern Malawi, and southern Tanzania.

Geological history

Malawi is one of the major Rift Valley lakes and an ancient lake. The lake lies in a valley formed by the opening of the East African Rift, where the African tectonic plate is being split into two pieces. This is called a divergent plate tectonics boundary. Malawi has typically been estimated to be 1–2 million years old (mya), but more recent evidence points to a considerably older lake with a basin that started to form about 8.6 mya and deep-water condition first appeared 4.5 mya.

The water levels have varied dramatically over time, ranging from almost 600 m (2,000 ft) below current level to 10–20 m (33–66 ft) above. During periods the lake dried out almost completely, leaving only one or two relatively small, highly alkaline and saline lakes in what currently are Malawi's deepest parts.

Geography

The alkaline Lake Rukwa lies midway between Lake Tanganyika and Lake Malawi at an elevation of about 800 metres (2,600 ft), in a parallel branch of the rift system. Almost half of the lake lies in Uwanda Game Reserve.

Hydrology

The lake has seen large fluctuations in its size over the years, due to varying inflow of streams. Currently it is about 180 kilometres (110 mi) long and averages about 32 kilometres (20 mi) wide, making it about 5,760 square kilometres (2,220 mi2) in size. In 1929 it was only about 48 kilometres (30 mi) long, but in 1939 it was about 128 kilometres (80 mi) long and 40 kilometres (25 mi) wide. During the early rifting of this part of Africa, the basin of Lake Rukwa may at times have been part of a much larger basin which also included the basins of Lake Tanganyika with Lake Malawi; ancient shorelines suggest a final date of overflow into Lake Tanganyika of 33,000 BPTooltip Before Present. For overflow to occur again, the lake's elevation would need to exceed 900 meters.

Description

This lake is fed principally by the Southern Ewaso Ng'iro River, which rises in central Kenya, and by mineral-rich hot springs. It is quite shallow, less than three metres (9.8 ft) deep, and varies in width depending on its water level. The lake is a maximum of 57 kilometres (35 mi) long and 22 kilometres (14 mi) wide. The surrounding area receives irregular seasonal rainfall, mainly between December and May totalling 800 millimetres (31 in) per year. Temperatures at the lake are frequently above 40 °C (104 °F).

High levels of evaporation have left behind natron (sodium carbonate decahydrate) and trona (sodium sesquicarbonate dihydrate). The alkalinity of the lake can reach a pH of greater than 12.

Hydrology and basin

Lake Manyara has a catchment area of about 18,372 km2 with elevations between 938 m and 3633 m above sea level. The lake is in a closed basin with no outflow, wherein water is only lost by evaporation. It is fed by underground springs, but the vast majority of the inflow comes from rainwater fed permanent and ephemeral rivers that drain the surrounding catchment. The lake's depth and the area it covers fluctuates significantly. At its maximum, during the wet season, the lake is 40 km wide by 15 km with a maximum depth of 3.7 m. In 2010, a bathymetry survey showed the lake to have an average depth 0.81 m, and a maximum depth of about 1.18 m. In extreme dry periods the surface area of the lake shrinks as the waters evaporate and at times the lake has dried up completely.