Formation of East Lake, Wuhan, Eastern China

The East Lake, located in the downtown of Wuhan city, Hubei Province, is the largest city lake in China or even in Asia. It is one of the first batches of national key scenic spots and 5A tourist attractions, and has been an important water source area for industrial, agricultural production and aquatic base in Wuhan. Nowadays, in Wuhan it building the ecological green heart of East Lake, therefore there is great significance for resources, environment, ecology and humanity. However, the formation cause of the East Lake has long been disputed. This study is the first one to analyze the origin of the East Lake from many aspects, including geology, geomorphology and sedimentation, further to discuss the relationship between the East Lake and the Yangtze River. The main conclusions are as follow: (1) The geomorphological characteristics of the lake: branching, meandering coastline and headlands and bays, this is generally developed on the hillock of Middle-Late Pleistocene. (2) The thickness of lacustrine sediments in East Lake is various, showing thin in the south and thick in the north, thin in the margin and thick in the middle. The underlying strata are mainly the Late Pleistocene Xiashu loess, and the Late Pleistocene slope layer is locally distributed near the southern margin of the bedrock residual mound. There is an obvious unconformable relationship between lacustrine sediments and Xiashu loess. (3) The basin of East Lake was formed in the last glacial maximum (LGM) about 20 ka ago. In this time, the sea level of the East China Sea has dropped sharply, and induced the riverbed of the Yangtze River incised. The Luojia, Nanwang and Yujia mountains on the south bank of the Yangtze River were deeply incised landscape when it flowed into the Yangtze River due to low erosion baseline of the LGM, resulting in a series of gullies. After that, the Holocene global warming and high sea-level, the water surface of the Yangtze River rose rapidly, and the natural dikes along its banks developed and expanded with resultant in filling of the incised gullies, accounted for the formation of lake. Based on the above analyses, the East Lake was a gully choked lake. (4) According to the characteristics of geology and geomorphology, the East Lake and Shahu Lake are two independent lakes with different formation processes. The Yangtze River does not flow through the East Lake, however, the formation of the East Lake is related to the Yangtze River, which is the result of the complex feedback of the East China Sea-Yangtze River-East Lake, this process was driven by global climate change.(5)The worth of the East Lake lies in nature. Protecting its natural characteristics and conforming its natural laws is principles of protection and utilization of the East Lake. As a whole, for the scientific concept of mountain-water-forest-paddy-lake-grass community, it is necessary to regard lake shore and landform as a whole and regard catchment and basin as a whole to protect and manage the East Lake in a holistic and systematic way.