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The Three Gorges region - comprising the Qutang, Wu, and Xiling gorges - is a series of breakthrough-valleys along the Yangtze River.
The starting point for the emergence of a breakthrough valley is usually a mountain that is oblique or transverse to the large-scale flow direction of a river. Over the course of millions of years, the river carries the mountains along a tectonic weakness or fault line. The breakthrough therefore often exposes the stratifications of the mountains in a clearly visible manner and allows conclusions to be drawn about the mountain formation. When mountain regions are rising - often still by 1 to 3 mm per year - some rivers will sink to the same degree. Debris and gravel are deposited at high tide in the basins of the upper reaches or below the breakthroughs, while fine gravel and sand mostly reach the main river. Due to the removal of material, the river cuts steadily further towards its source into the underground. This process is called retrograde erosion.
Breakthrough-valleys are divided on the basis of their origin in antecedent, epigenetic and Overflow breakthrough-valleys.
Antecedent breakthrough-valleys are valleys of rivers which direction exists before the onset of mountain uplift. The river cuts into the rising mountains a river bed instead of having to relocate.
Epigenetic breakthrough-valleys are valleys, which originally arose on loose rocks, covering a buried ridge. By deep erosion the river was in a position to incise in the mountain back and thus to form the valley.
Overflow breakthrough-valleys caused by the fact that behind of a naturally deposited debris mass (eg landslide) water dams and finally overflows at the lowest point.
Other well-known breakthrough valleys:
- The Kali Gandaki in Nepal, deepest breakthrough valley in the world, between the mountains Dhaulagiri und Annapurna
- The Iron Gate (Danube River) by the Southern Carpathians between Serbia and Romania
- The Red Towerpass in the middle reaches of the Olt, Romania
- The Delaware Water Gap (Delaware-breakthrough) in the Appalachian Mountains between the U.S. states of New Jersey and Pennsylvania
- The Manawatu Gorge on North Island of New Zealand
1. What kind breakthrough valley will you find here? Justify your answer.
2. Depending on the season you travel the Yangtze. What is the main difference when travelling in wet season (June – September)? What are you able to see?
3. Have a look at the mountain face. Ist he valley u-shaped or v-shaped? What is the inclination angle?
4. What will you find at the coordinates in order to observe the mountains more closely? Describe the features of the rocks (e.g. colour, structure and surface)?
The coordinates might not be very accurate. Travelling in the Gorge there is typically a stop. You can answer the question there.
5. How wide ist he valley at the given coordinates?
三峡地区 - 包括瞿塘，吴和西陵峡 - 是长江沿岸的一系列突破性山谷。
突破谷的出现的起点通常是倾斜或横向于河流的大规模流动方向的山。在数百万年的过程中，这条河沿着构造的弱点或断层线载着山脉。因此，突破经常以清晰可见的方式暴露山脉的分层，并且可以得出关于山地形成的结论。当山区上升 - 通常每年仍然增加1至3毫米 - 一些河流将下降到相同的程度。 碎屑和砾石在涨潮时沉积在上游盆地或突破口下方，而细砂砾和沙子大部分到达主要河流。由于物质的清除，河流进一步向源头进入地下。这个过程称为逆行侵蚀。
先行突破 - 河谷是河流的山谷，其方向存在于山脉隆起之前。这条河流入冉冉升起的山脉河床而不是搬迁。
表观遗传突破 - 山谷是山谷，最初出现在松散的岩石上，覆盖着埋藏的山脊。通过深度侵蚀，河流能够在山体中切割，从而形成山谷。
溢流突破 - 由于自然沉积的碎屑质量（例如滑坡）水坝背后最后溢出的事实造成的波谷。
- 尼泊尔的Kali Gandaki，世界上最深的突破谷，位于Dhaulagiri和Annapurna之间
(No hints available.)