Lake Kivu is one of the Great Lakes of Africa. It is on the border between the Democratic Republic of the Congo and Rwanda, and is situated in the Albertine Rift, a part of the Great Rift Valley. Lake Kivu empties into the Ruzizi River, which flows southwards into Lake Tanganyika. The lake covers a total surface area of some 2,700 km2 (1,040 sq mi) and stands at a height of 1,460 metres (4,790 ft) above sea level. The lake bed sits upon a rift valley that is slowly being pulled apart, causing volcanic activity in the area, and making it particularly deep, its maximum depth of 480 m (1,575 ft) is ranked fifteenth in the world. The lake is surrounded by majestic mountains. The world's tenth-largest inland island, Idjwi, lies in Lake Kivu, while settlements on its shore include Bukavu, Kabare, Kalehe, Sake and Goma in Congo and Gisenyi, Kibuye and Cyangugu in Rwanda. Native fish include species of Barbus, Clarias, and Haplochromis, as well as Nile Tilapia. Limnothrissa miodon, one of two species known as the Tanganyika sardine, was introduced in 1959 and formed the basis of a new pelagic zone fishery. In the early 1990s, the number of fishers on the lake was 6,563, of which 3,027 were associated with the pelagic fishery and 3,536 with the traditional fishery. Widespread armed conflict in the surrounding region from the mid-1990s resulted in a decline in the fisheries harvest. Lake Kivu is one of three known exploding lakes, along with Cameroonian Lake Nyos and Lake Monoun, that experience violent lake overturns. Analysis of Lake Kivu's geological history indicates a periodic massive biological extinction about every 1,000 years. The trigger for lake overturns in Lake Kivu's case is unknown but periodic volcanic activity is suspected. The gaseous chemical composition of exploding lakes is unique to each lake; in Lake Kivu's case, methane and carbon dioxide due to lake water interaction with a volcano. The amount of methane is estimated to be 65 cubic kilometer and of carbon dioxide 256 cubic kilometer. The risk from a possible Lake Kivu overturn would be catastrophic, dwarfing other documented lake overturns at Lakes Nyos and Monoun, since approximately two million people live in the lake basin.
Lake Kivu, located 100 miles north of Lake Tanganyika at the highest point of the East-African Rift Valley (approximately 1500m in elevation), is one of three known volcanic lakes in the world that contain high dissolved volumes of CO2 in their deeper waters; the other known volcanic lakes are Lake Nyos and Lake Monoun in Cameroon (Degens et al, 1973; Witze, 2002). Lake Kivu has remained stably stratified for thousands of years; however, in the last few decades much attention in the scientific field has been directed towards the lake. A heat flux into the lake, or other meteorological and limnological forces may cause an overturn, or later described rollover, of the lake releasing the dissolved CO2 from pressure and causing a discharge of gas that could devastate communities located on or near the lake (Rice, 2000; Kling, 1989). Lake Kivu sits very close to the neighboring Nyiragongo Volcano in the Democratic Republic of the Congo. Lake Kivu is the largest of numerous freshwater lakes that shimmer in the valleys of Rwanda. Steep terraced hills lead down to the picturesque lake shore, and three resort towns, Gisenyi, Kibuye and Cyangugu, are an ideal stopping point to relax, swim, or take a boat excursion past the small lakeside villages that offer a rewarding glimpse of rural life. Set amid the dramatic mountains of the rift valley and the volcanic Virungas to the north, the irregular shores of Lake Kivu form numerous inlets and peninsulas and myriad forest-fringed waterfalls. The lake is a 2650 square kilometre freshwater expanse and the largest of all the lakes that fill the valleys of Rwanda. The beautiful lake is enclosed by the steep terraced hills that are characteristic of rural Rwanda and sitting on its shores are the three lakeside towns of Cyangugu, Kibuye and Gisenyi; the perfect tourist transit points between the Chimpanzee tracking destination of Nyungwe Forest National Park in the south, and gorilla tracking in Parc National des Volcans in the north.
Lake Kivu has never had a lake overturn but along with Monoun and Nyos it is one of the three lakes in the world which contain such large amounts of carbon dioxide making it very possible that the lake could overturn at some point. The lake is 2000 times bigger than Lake Nyos and has a population of two million people living around its shores. Professor Robert Hecky (University of Michigan) took samples of the sediments of Lake Kivu which gave a record of the history of the lake going back several thousand years. This showed that approximately every thousand years an event occurred which caused all living creatures in the lake to be wiped out and huge amounts of vegetation to be swept into the lake, which is consistent with a lake overturn. If the lake was to overturn huge amounts of carbon dioxide would be released, suffocating millions of living creatures, but the lake also contains a large amount of methane which could cause explosions above the lake. Kivu contains enough methane to power the US for a month, and five times as much carbon dioxide – about 200 km3. The waters of Lake Kivu manifest a particularly obvious 'stair-like' stratified structure following the variations of their physico-chemical parameters with depth. The exact explanation of this phenomenon of stratification is complex. The waters of the lake are made up of homogenous layers - where mixing by convection easily takes place - separated by layers with a high density gradient which act as barriers to the mixing process. A Franco-Swiss team of scientists is studying the physico-chemical makeup of the lake, its evolution through time, the origin of the dissolved gases and an evaluation of the risk of a gas explosion.
