Lake Tanganyika is located in the Western Rift Valley in East Africa's Great Rift Valley. As Africa's second largest lake and oldest rift lake, Tanganyika's age is dated between 9 and 12 million years old, though one source claimed 20 million. While the vast majority of Earth's lakes are only several thousand years old, Tanganyika's age is due to the type of lake it is. Typical lakes accumulate sediment until they become filled in completely, but lakes like Tanganyika never accumulate sediment because they experience constant downward expansion called downfaulting. These lakes are known as graben lakes, and those in the Great Rift Valley of Africa were created as water filled in the depressions formed by tectonic activity. While sediment deposition still occurs in Tanganyika, as it does in all lakes, accumulation is negated by this downfaulting. As a result of no sediment accumulation and the subsequent old age of the lake, Tanganyika has acquired one of the richest ecosystems of any freshwater body.
The downfaulting is also responsible for Tanganyika's incredible size and depth. The maximum depth of the lake is an astonishing 1470 meters (4,820 ft), making it the second deepest lake in the world!
Lake Tanganyika's surface area is shared by the Democratic Republic of Congo (45%), Tanzania (41%), Burundi (8%), and Zambia (6%). While Rwanda does not border the lake itself, it borders Lake Kivu which connects to Tanganyika through the Ruzizi River and is therefore part of the watershed. The lake is the major form of transportation and travel for populations in the area. Only one main road lies along the lake edge, and most roads go straight to the lake. Fishing is the primary source of protein for the majority of the populations within the watershed.
Due to the nature of radiation of the lake's flora and fauna, Tanganyika has a high proportion of endemic species. There is a thriving market for many species of cichlid fish, which make up 63% of the unique animal species found in the lake. This market is one of Tanganyika's most well known features, as collectors have taken a huge interest in the numerous unique exotics. (For more information on cichlids, other fish, and radiation speciation, please click Biotic Information here, or navigate to it under the Home button above.)
As the northern regions of the lake have seen population growth, the environment has seen it's consequences. Unregulated conversion of forests to agricultural land resulted in rapid surface erosion. According to Ruud C. M. Crul's 1997 book on the limnology of Lake Tanganyika, forests in the northernmost portions are nearly 100% cleared and 50% in the center portions. The environmental impacts of the erosion can be seen in the increased sediment loads of the rivers and the nearshore lake waters. Crul refers to a study from 1991 to 1993 which claimed that the increased sediment load has already had a serious negative impact on biodiversity. (Click here to read this study.)
Pollution presently stands as the greatest threat to the ecosystem. While the large size of the lake would lead one to believe that human activity might have little impact on the water quality, the very long flushing period prevents replenishing of the water. In the northern end of the lake as well as the cities Kalemie, Kigoma, Kipili, and Mpulungu elsewhere, the waste from municipalities, agriculture, and industries are untreated and discharged directly into the lake. (For more information on the hydrodynamics and water statistics of the lake, please click here, or navigate to it under the Home button above.)
As you read above, the Great Rift Valley and its lakes were formed from tectonic activity many millions of years ago. Upward movement of the crust coupled with volcanic activity in the Miocene (25-12 million years before present, geologic timeline) created valleys and ridges with a general north to south orientation. Further tectonic activity split the earth's crust, and over time they were filled with water from rivers and rainfall.
Tanganyika is hypothesized to have three stages of geologic development, which may be why Pierre Brichard put the age of the lake to 20 million years, as referenced in the "General Information" above.
While the lakes themselves have roughly persisted as the same entities since this time, there have been significant differences in water levels due to climatic variation.
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Around 35,000 years ago, the level fell 150 meters. From the patterns and chemicals found in the in the sediment cores from the regions of the lake above that level and dated to this time period, researchers found that there were extensive swamp regions. Another 13,000 years of decreasing water level persisted, and from 22,000 years to 15,000 years before present the lake was 300 meters below the current level.
Tectonic activity increased again, and around 9,500 years ago the Virunga volcanoes rose and blocked Lake Kinu's drainage to the Nile River system. The flow of water subsequently poured into Lake Tanganyika and established the Ruzizi River of present, as well as created an outflow for the lake through the Lukuga River.
A cooler and drier climate around 3,500 years ago cut off inflow from the Ruzizi River and outflow through the Lukuga, and the lake level dropped 75 meters below the current level. For the next few thousand years until present, the water level in Tanganyika gradually rose to current levels.