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Danube Delta
The Danube Delta ((ルーマニア語、モルドバ語():Delta Dunării) ; (ウクライナ語:Дельта Дунаю, ''Del'ta Dunaju'')) is the second largest river delta in Europe, after Volga Delta, and is the best preserved on the continent.〔(Danube Delta - UNESCO World Heritage Centre )〕 The greater part of the Danube Delta lies in Romania (Tulcea County), while its northern part, on the left bank of the Chilia arm, is situated in Ukraine (Odessa Oblast). The approximate surface area is , and of that, are in Romania. With the lagoons of Razim-Sinoe ( with water surface), located south of the main delta, the total area of the Danube Delta reaches . The Razelm - Sinoe lagoon complex is geologically and ecologically related to the delta proper and their combined territory is part of the World Heritage Sites.
==Geography and geology==
The modern Danube Delta began to form after 4000 BCE in a bay of the Black Sea, when the sea rose to its present level. A sandy barrier blocked the Danube bay where the river initially built its delta. Upon filling the bay with sediments, the delta advanced outside this barrier-blocked estuary after 3500 BCE, building several successive lobes:〔Giosan et al., 2006, Young Danube delta documents stable Black Sea level since the middle Holocene: Morphodynamic, paleogeographic, and archaeological implications, ''Geology'', 34, 757–760 (2006). ()()〕 the St. George I (3500-1600 BCE), the Sulina (1600-0 BCE), the St. George II (0 BC-Present) and the Chilia or Kilia (1600 CE to present). Several other internal lobes were constructed in the lakes or lagoons bordering the Danube delta to the North (Chilia I and II) and toward the South (Dunavatz).〔Giosan et al., 2009, Early Anthropogenic Transformation of the Danube-Black Sea System, ''Scientific Reports'', 2, 582, ()()〕 Much of the alluvium in the delta and a major expansion of its surface area in the form of lobes resulted from soil erosion associated with clearing of forests in the Danube basin during the 1st and 2nd millennium. Geologist Liviu Giosan told ''The New York Times'' that:
Probably 40 percent of the Delta was built in the last 1000 years. Finding that was like a eureka moment.”〔
At present the delta suffers from a large sediment deficit after the construction dams on Danube and its tributaries in the later half of the 20th century. However, construction of a dense network of shallow channels in the delta over the same period attenuated the deficit on the delta plain but increased erosion at the coast 〔Giosan et al., 2009, Maintenance of large deltas through channelization: Nature vs. humans in the Danube delta. Anthropocene.〕〔http://www.whoi.edu/news-release/maintaining_deltas〕 The Danube Delta is a low alluvial plain, mostly covered by wetlands and water. It consists of an intricate pattern of marshes, channels, streamlets and lakes. The average altitude is 0.52 m, with 20% of the territory below sea level, and more than half not exceeding one meter in altitude. Dunes on the most extensive strandplains of the delta (Letea and Caraorman strandplains) stand higher (12.4 m and 7 m respectively). The largest lakes are Dranov (21.7 km2), Roșu (14.5 km2), Gorgova (13.8 km2).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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