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如何漫长的河流的存在吗?

我最近在一个长途飞行在西伯利亚上空,它给我的印象是相当显著的勒拿河可能存在。似乎很奇怪,有一个从贝加尔湖附近的一些随机点超过2800英里左右的北冰洋,一路下坡。同样,密苏里河告诉我们,有一个更长的downhill-only从某个地方在蒙大拿墨西哥湾。

但这些东西肯定确实存在,它是一个世界各地的模式重复:绝大多数的地球表面是由河流排水下坡跑到大海。他们不困,他们似乎并没有形成大量的湖泊有洪水面积提高水位在一些障碍。我知道的内陆河流域海洋不流失,但他们只覆盖大约18%的陆地表面,主要在中亚。

是长下坡路线的存在比我想象的更有可能吗?(我不知道如果我认为这是更有可能在山区比在平坦地区,这说明我对这个可怜的直觉)还是地球只是一个巧合?河流使下坡路径本身吗?

回答

我将尝试这些考虑后挖出你的有趣的问题:1。在大陆范围内,流水没有显著的惯性,所以水流后,* * * *最大斜率。河是一条沿着大陆之后的最大局部斜率在任何地方通过。2。让你感到惊奇的(让我解释)是大陆大部分由河流排水流量不断* * * * *下坡的*。当水缺乏一个下坡的路(地方地形最低),它形成了一个湖。所以,引人注目的是,有这样的地形最小值相对较少,湖泊和沼泽,在我们的大陆。3所示。如果河流海洋中结束,它早已是由大陆和它的曲折度的大小。如果它以一个内陆河盆地(关闭,internally-drained,陆内),然后通过定义河流将形成一个湖泊最低的盆地。 4. Because continents are above the level of the surrounding ocean, it is clear that between any location at the continent and the coast, every path will be, on average, downslope. Continental areas below sea level are by definition endorheic (see 3) and therefore they drain to internally-drained lakes. 5. Provided some slope, erosion makes the river network gradually entrench the terrain at typical rates of 0.01 to 1 mm/yr. Rivers move laterally more easily at very flat regions, where they loose energy and deposit their sediment load, forming meanders and marshes. Over geological time, the river network, together with other *surface transport* processes, make the landscape decay towards a flat (peneplain) surface at the level of the ocean. So what would be the opposite to a landscape dominated by long rivers? Answer: Having many locations with no downhill slope to follow, topographic minima (basins) where **lakes** form. Therefore your question reduces to this one: **"Why aren't there more lakes?"** The 117 million lakes on Earth occupy only 4% of the land surface[1]. The rest of the continental surface has a downhill slope for water to flow. Even endorheic drainage basins are drained mostly by rivers, although these drain to close lakes instead of the ocean. Importantly, large lakes are relatively rare because they are ephemeral: once they form by tectonic and geodynamic changes of the topography they tend to disappear due to two processes: A) Lake basins tend to fill up with the sediment carried by tributary rivers[2]. B) Lake basins tend to be lowered in level due to the erosion along their outlet river[3], see my point #5 above. Consider a landscape formed with a purely random topography. It will contain many lakes because their steepest descent path will not lead to the sea. Processes A and B would tend to fill the lakes and erode their outlets, making this topographic minima disappear and establishing a *normal* fluvial network with progressively fewer lakes. On Earth, erosion is a process trying to remove lake basins in timescales of hundreds of thousands to tens of millions of years, depending on the size or elevation of the lake and its drainage basin. If we still have this 4% of the planet surface occupied by lakes it is because river erosion competes with relief-generating mechanisms such as plate tectonics or glaciers. But that's a different story. [1]: National Geographic: [117 Milion lakes in the planet](http://voices.nationalgeographic.com/2014/09/15/117-million-lakes-found-in-latest-world-count/). [2]: Carroll, A.R., and Bohacs, K.M., 1999, Stratigraphic classification of ancient lakes: Balancing tectonic and climatic controls: Geology, v. 27, p. 99–102, doi:10.1130/0091-7613(1999)027<0099:SCOALB>2.3.CO;2. [3]: Garcia-Castellanos, D., 2006. Long-term evolution of tectonic lakes: Climatic controls on the development of internally drained basins. In: Tectonics, Climate, and Landscape evolution. Eds.: S.D. Willett, N. Hovius, M.T. Brandon & D.M. Fisher. GSA Special Paper 398. 283-294. doi:10.1130/2006.2398(17)

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\ begingroup美元 “只有当他们到达河流横向移动非常平坦的地区”——这不是真的。河流不断雕刻的山边。他们肯定横向移动速度和极在山区,但他们仍然移动。 \ endgroup美元
- - - - - -naught101
2017年2月21日在22:56
\ begingroup美元你是对的,我将会改变 \ endgroup美元
- - - - - -DrGC
2017年11月7日在十四16
\ begingroup美元一个小湖组成的1903人弗兰克的幻灯片几乎已经满是泥沙。 \ endgroup美元
- - - - - -基思·麦克
2017年11月9日20:22

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