15 natural lakes that cross the political boundaries The East African rift system (EARS) Great Rift Valley of East Africa (Afro-Arabian rift system). 1 Gash River Lakes of Ethiopia East African Plateau EastEast AfricanAfrican RiftRift 2 Comparison between Western Rift and Eastern Rift Western Rift Eastern Rift . Center is high Center is high . Bilateral Normal faults Left Normal faults . 40-50 km wide 50-100 km wide . Less higher elevation Higher elevation (2,000m) . Bounded by fault zones Not Necessarily . Granite, Localized volcanism Extensive volcanism . Large, elongated, deep lakes Small shallow lakes . Mostly Freshwater Mostly alkaline water . Fluvial influent and effluent Mostly closed basins White Nile Blue Nile Tana 3 Ziway Langano Shala t if Awassa R n ia p Abaya io th E Chamo Estifanos Turkana East African Plateau EasternEastern RiftRift LakesLakes 4 Sodium carbonate Soda Ash: Anhydrous sodium carbonate Na2CO3 Brines: Sodium carbonate-rich waters Na2CO3.H2O Nahcolite (NaHCO3) Trona [(Na2CO3) (NaHCO3) 2(H2O) ] (Na3H(CO3)2.2H2O) Water dissolves Na2CO3 from weathered volcanic Rocks. Closed lakes, Evaporation Trona No. of lakes: Uganda 69 Kenya 64 Turkana Tanzania 49 Ethiopia 46 69 64 Baringo Bogoria Nakuru Elmenteita Naivasha Victoria Magadi Natron Eyasi Manyara 49 5 Ethiopia Sudan Omo R. Uganda Turkwel R. Kenya Somalia Kerio R. N Omo R. Turkwel R. Kerio R. Geology of Turkana basin. 6 Omo River Delta >90% Turkana Albert Kioga George Tuff Edward Victoria Kivu Tanganyika Turkwel R . Area : 7,600 km2 Depth : 31 m Volume: 251 km3 Salinity: 2,500 mg/L, Kerio R. EC = 3,300 µS No outlet Early Miocene Highly alkaline 9.5 Lake Turkana Physiographic data of the lakes in the Eastern Rift in m and m3. ‰ 31 7 A B Naivasha Turkana Baringo 1,884 m Albert Kioga 965 m Fresh A pH=8.8 pH=8.1 George Fresh Underground outlet Edward Victoria B Loboi Plain Kivu Bogoria Tanganyika 990 m 200 hot sp pH=10 Small, Shallow 10 m Altitude: Center high Salinity: Brines Hot springs No outlet Magadi Early Miocene 575 m Nakuru Highly alkaline >10 Trona 1,758 m Elmenteita Half-graben 1,776 m Ephemeral lakes Lake Naivasha 1,900 m asl, 600 km2 Fresh Underground outle Soda Intermittent (0.35 km3) Natural 8 Trona Turkana Albert Kioga Trachytes Lake George Magadi Edward Salinity 2.0-3.1% Victoria 575 m Kivu Tanganyika Soda Ash Lake (Na CO ) 2 3 Natron Trona {(Na2CO3) (NaHCO3) 2H2O} 5 km Gelai volcano March 8, 2003 Salt-loving microorganisms have colored the lake’s salt Trona crust red or pink . 5 km 9 Turkana Albert Kioga Lake George Manyara phosphate Edward Victoria Kivu Lake Eyasi Tanganyika Lake Lake Burungi Kitangiri Small, Shallow 3 m Altitude: Center high r Salinity: 2.5 ‰ e iv R Hot springs e r e b No outlet m e W Highly alkaline >10 Half-graben Ephemeral lakes Turkana Albert Kioga Lake George Manyara phosphate Edward Victoria Kivu Lake Eyasi Tanganyika Lake Lake Burungi Kitangiri Small, Shallow 3 m Altitude: Center high r Salinity: 2.5 ‰ e iv R Hot springs e r e b No outlet m e W Highly alkaline >10 Half-graben Ephemeral lakes 10 Classification of Rift African Lakes based on Conductivity Class I: Low ion concentrations <600 µS/m microsiemens (µmho, micromhos) E.g. Malawi, Victoria, Tana, George Class II: Moderate ion concentrations 600 – 6,000 µS/m E.g. Tanganyika, Kivu, Edward, Albert, Turkana (Rudolf), Rukwa Class III: High ion concentrations 6,000 – 160,000 µS/m E.g. Ethiopia (Lake Zawi, Shala, and Abaya) Gregory (Magadi, Natron, Manyara, Eyasi) East African Plateau WestWest AfricanAfrican RiftRift LakesLakes 11 Edward 914 m Rutshuru River Virunga L. Bulera Volcanoes Victoria Volcanoes L. Luhonde 1,134 m Kivu Kivu 1460 m To Kagera Volume : 570 km3 and L. Victoria Area : 2,699 km2 Depth : 485 m Salinity : 1.12% Ruzizi River volcanic barrier lakes Tanganyika 773 m Great Lakes 12 Ruzizi River Turkana Albert Kioga George Edward Victoria Kivu Tanganyika Lake Tanganyika 733 m • Deepest lake in Africa 1471m • Longest lake 670 x 50 km • Area: 33,500 km2 • Volume: 19,000 km3 (58%) • Salinity (0.53%). Lake Rukwa Ruzizi River Turkana Albert Kioga George Edward Victoria Kivu Tanganyika Lake Tanganyika 733 m • Deepest lake in Africa 1471m • Longest lake 670 x 50 km • Area: 33,500 km2 • Volume: 19,000 km3 (58%) • Salinity (0.6%). 13 14 7 1 2 9 5 Largest Lakes (area) 15 1 3 2 Largest Lakes (volume) • Enclosed Lake • Shallow lake 3-5 m • 320 x 40 km • Area: 2,716 km2 • Drainage: 81,000 km2 • Salinity (0.53%). Lake Rukwa 16 East African Plateau MedianMedian RiftRift LakesLakes 17 150 km Nyasa Malawi Niassa Lake Malawi Niassa Nyasa • 600 x 50 km • A = 28,800 km2 L. Malombe 18 90 80 70 60 50 Area (100040 sq km) 30 69 20 10 0 Superi or Victori a Huron 25.0 Mic 32 20.0 higan 15.0 Tangan yika 5 10.0 Volume (1000 cubic km) 18.9K Baikal 5.0 Great 0.0 Bear Tonle S 29 Baikal ap Mal 9 Tanganyika awi 8.4K Aral Superior Sea Malawi Michigan Huron 2.7K Victoria Great Bear Great Slave Issyk-Kul 19 Max. D. 770 m Ave. D. 292 m 90% above 100 m East African Plateau 20 1,600 Kivu 1,400 1,200 m 1,000 Edward Rukwa 800 Tanganyika Chilwa 600 Albert Altitude, Altitude, 400 Malawi 200 0 Lake Lake Malawi Tanganyika 21 Lake Lake Malawi Tanganyika Lake Lake Malawi Tanganyika 22 http://www.pecad.fas.usda.gov/cropexplorer/global_reservoir/gr_regional_chart.aspx?regionid=safrica&reservoir_name=Tanganyika Lake Lake Malawi Tanganyika Basin Basin Basin/Lake 8:1 Basin/Lake 3:1 23 150 km Lake Malawi Malombe Chilwa Shire River Ruzizi River Salinity Salinity 0.19 ‰ 0.53‰ Lake Lake Malawi Tanganyika Shire River 24 2.5 million km2 8% of Africa 10,000 - 25,000 km2 Recently 1,350 km2 Basin/Lake 100 : 1 Altitude 250 m 25 ++++ Chad border Ancient Basin Sub-basins 8 m 5 m Average depth 1.5 m 26 Komadougou- Yobe River Chari / Logone 95% (40-10 km 3) October 21, 2001 27 1900 1950 28 Shrinking Lake Chad shared by Nigeria, Niger, Chad and Cameroon Persistent drought has shrunk the lake to about a tenth of its former size • 1972: Larger lake surface area is visible in this image • 2001: Impact of drought displays a shrunken lake, comparatively much smaller surface area than in 1972 image 29.