|
Lake Victoria (''Nam Lolwe'' in Luo; "Nalubaale" in Luganda; ''Nyanza'' in Kinyarwanda and some Bantu languages〔(【引用サイトリンク】url=http://www.wdl.org/en/item/2557 )〕) is one of the African Great Lakes. The lake was named after Queen Victoria by the explorer John Hanning Speke, the first Briton to document it. Speke accomplished this in 1858, while on an expedition with Richard Francis Burton to locate the source of the Nile River. With a surface area of , Lake Victoria is Africa's largest lake by area, and is also the largest tropical lake in the world. Lake Victoria is the world's second largest freshwater lake by surface area; only Lake Superior in North America is larger. In terms of its volume, Lake Victoria is the world's ninth largest continental lake, and it contains about 2,750 cubic kilometers (2.2 billion acre-feet) of water. Lake Victoria receives its water primarily from direct precipitation and thousands of small streams. The largest stream flowing into this lake is the Kagera River, the mouth of which lies on the lake's western shore. Lake Victoria is drained solely by the Nile River near Jinja, Uganda, on the lake's northern shore. Lake Victoria occupies a shallow depression in Africa and has a maximum depth of and an average depth of .〔United Nations, ''Development and Harmonisation of Environmental Laws Volume 1: Report on the Legal and Instituional Issues in the Lake Victoria Basin'', United Nations, 1999, page 17〕 Its catchment area covers 184,000 square kilometers (71,040 sq mi). The lake has a shoreline of , with islands constituting 3.7% of this length, and is divided among three countries: Kenya (6% or ), Uganda (45% or ) and Tanzania (49% or ).〔J. Prado, R. J. Beare, J. Siwo Mbuga & L. E. Oluka, 1991. A catalogue of fishing methods and gear used in Lake Victoria. UNDP/FAO Regional Project for Inland Fisheries Development (IFIP), FAO RAF/87/099-TD/19/91 (En). Rome, Food and Agricultural Organisation.〕 ==Geology== During its geological history, Lake Victoria went through changes ranging from its present shallow depression, through to what may have been a series of much smaller lakes.〔 Geological cores taken from its bottom show Lake Victoria has dried up completely at least three times since it formed.〔 These drying cycles are probably related to past ice ages, which were times when precipitation declined globally.〔 Lake Victoria last dried out 17,300 years ago, and it refilled beginning about 14,700 years ago. Geologically, Lake Victoria is relatively young – about 400,000 years old – and it formed when westward-flowing rivers were dammed by an upthrown crustal block. This geological history probably contributed to the dramatic cichlid speciation that characterises its ecology, as well as that of other African Great Lakes, although some researchers dispute this, arguing while Lake Victoria was at its lowest between 18,000 and 14,000 years ago, and it dried out at least once during that time, there is no evidence of remnant ponds or marshes persisting within the desiccated basin. If such features existed, then they would have been small, shallow, turbid, and/or saline, and therefore markedly different from the lake to which today's species are adapted. The shallowness of Lake Victoria, its limited river inflow, and its large surface area compared to its volume make it vulnerable to the effects of climate changes. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lake Victoria」の詳細全文を読む スポンサード リンク
|