PLATE F-3
HUANG HE, SHANXI PROVINCE, CHINA

Plate F-3	Map

This specially processed Landsat scene, produced by Earth Satellite Corporation, shows the Fen River (Fen He) valley immediately south of the Taiyuan Basin. The Fen He has developed a broad alluvial plain that has terraces overlain with thin loess. Flat loess areas (yuan) dominate in the lower left of the scene, where the Fen He flows into the Huang He (Yellow River). Highly dissected "liang" topography forms a sharp contact with the Yuan surface.

The Landsat scene immediately to the west (E-152502455-7) is shown in Figure F-3.1. It shows the Huang He valley through typical liang surfaces of the Loess Plateau. FigureF-3.2 depicts the Huang He and its valley elsewhere in the region. The dissected uplands shown in Figure F-3.3 are characteristic of nearby loess plateaus.

Figure F-3.1	Figure F-3.2

The contrast between the alluvial plains and the dissected loess plateau is especially striking on the imagery. The alluvial plains are characterized by modern floodplains and terraces. Terraces are abandoned floodplains formed when rivers flowed at higher levels than at present. Changes in river position within the valley occur because of changes in the major controls on channel gradients and patterns. In the Loess Plateau, it is probable that past changes in discharge and sediment load were induced by major climatic changes during the Pleistocene. The rivers responded by cycles of aggradation and degradation that were superimposed on the long-term trend of valley incision. Terraces formed when floodplain levels were abandoned by subsequent river incision.

Traditional opinion inside China, going back to at least 32 B.C., has consistently held that the loess is primarily an eolian sediment derived from the deserts to the north and west. Recent work has confirmed this hypothesis, showing that loess accumulation followed the desiccation of the high central Asian plateaus in the early Pleistocene. A severe periglacial environment prevailed during glacial periods, associated with prevailing northwesterly winds. The dust blowing from the cold dry plateaus was trapped by the southeasterly climatic gradient toward humid subtropical monsoonal areas of China.

Figure F-3.3

Loess is perhaps the most easily erodible material available to moving water. As a result, the sediment loads of the Huang He are greatly in excess of those for any other large river in the world. Where it leaves the loess plateau, the Huang He is estimated to transport between 1.5 and 1.9 billion metric tons of sediment per year. Much of that load is transported to the Yellow River delta (Figure 5-1) and the Gulf of Bo Hai. The Yellow Sea, of which the gulf is the western arm, derives its name from the immense load of sediment that is delivered to it.

Interestingly, the river delivers its immense load with a relatively small water discharge: 49 km³/yr or an average of 1550 m³/s (Milliman and Meade, 1983). This contrasts with the nearby Yangtze River (Chang Jiang), which does not drain loess. The Yangtze delivers less than one-third the sediment, but its discharge is nearly 20 times as great. The unique qualities of the Huang He give it the highest sediment concentrations of any major river. Average yearly concentrations of sediment in Huang He water are as great as 48 g/liter and average monthly concentrations can exceed 70 g/liter. Landsat 30597-02293-7, October 23, 1979.