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Why Mountains Stop Growing
山脈為什么停止上升了
If you live up in the mountains, understanding the continually shifting landscape can mean survival.
如果你居住在山上，了解持續不斷移動的風景就意味著生存。
Mountains are continually shifting? Because of the erosion? Not just erosion.
山脈是不斷移動的嗎？因為侵蝕？不僅僅是因為侵蝕。
Erosion wears mountains down, but active mountain ranges are also continuously rising. And here's the interesting thing: despite this, once mountains reach a certain height, they achieve a state of equilibrium. So they rise but do not get any taller? Weird.
侵蝕磨損山體使之高度下降。但是活躍的山脈也同樣不斷在上升。這有個有趣的現象：盡管山脈會不斷上升，但上升到一定高度后，它們就達到一種平衡狀態。所以它們上升但高度不會繼續增加？真不可思議。
You see, mountain ranges form in places where tectonic plates meet—those are the thick sheets of rigid rock that cover the earth's surface. When one tectonic plate slides beneath the other, the parts of it that are scraped off pile up in buckling folds to form mountains.
你看。山脈是在地殼板塊交接的地方形成的，地殼板塊是覆蓋地球的堅硬巖石厚片。當某地殼板塊俯沖到另一板塊下面時，被摩擦掉的那部分巖石就以褶皺的形式堆積起來形成山脈。
Of course, we're talking geological time here, which is measured in tens of thousands of years. So one question geologists are investigating is which forces counteract the shifting and colliding of the tectonic plates and enable still-active mountain ranges to level off at a certain height.
當然，我們現在談論的是地史時期，是以數萬年測量的。因此地質學家一直研究的一個問題就是哪些力量中和了板塊的移動和碰撞，并使得仍活躍的山脈在某一特定高度呈平衡狀態。
And that's where erosion comes yet. Yes, but erosion is caused by many factors, like weather and rivers carving into the mountains. Also, as mountains get higher, they get steeper, and the greater the slope, the more sediment ends up sliding down into the oceans instead of accumulating on the mountains themselves.
那就是侵蝕出現的原因了。是的，但是侵蝕是由多種原因引起的，比如天氣和侵蝕山脈的河流。同樣，山脈變高時，他們也變陡峭了，坡度越大，就會有越多的沉積物滑向海洋，而不是堆積在山脈上。
So the big question is what role each of these factors plays in maintaining the height of mountain ranges. And that's where the debate comes in—and it's a tough one.
所以最大的問題就是這些因素在保持山脈高度時各自扮演著什么角色。而且那就是爭論的源頭——是個難題。
