55 Waterfalls-Mid

Waterfalls FOCUS Question How are landforms and waterfalls interrelated?

瀑布焦点问题地貌和瀑布是如何相互关联的?

Wonderful Water It seems as if the dry desert canyon will never end. The sun beats down on your skin as you trudge up the steep slopes. Soon the walls of the canyon grow tall and narrow, casting cool shade. You hear the most wonderful sound— rushing, flowing, gurgling water. Despite the heat you hike on, and around a corner you find a beautiful surprise. A shimmering waterfall roars and splashes into a clear blue pool. Waterfalls are some of the most beautiful and inspirational natural features. You can find them in mountains and rainforests, and near beaches. Even in deserts, wherever a river meets a drop-off, a waterfall is born. How do waterfalls form, and why do they occur in some places but not others?

干燥的沙漠峡谷似乎永远不会结束。 当你艰难地爬上陡峭的山坡时，阳光直射在你的皮肤上。 很快峡谷的岩壁变得又高又窄，投下凉爽的阴影。 你会听到最美妙的声音——流水潺潺。 尽管天气很热，但在拐角处你会发现一个美丽的惊喜。 一个闪闪发光的瀑布咆哮着，溅进一个清澈的蓝色水池。 瀑布是最美丽和最鼓舞人心的自然特征之一。 你可以在山区、热带雨林和海滩附近找到它们。 即使是在沙漠中，河流在任何地方汇合，瀑布就会诞生。 瀑布是如何形成的，为什么它们只出现在某些地方而不是其他地方?

What Makes a Waterfall? A waterfall needs two parts—a stream or river and a steep section of land. The water flows over a slope, ledge, or cliff. Some waterfalls, called falls, drop vertically through the air. Others, called cascades tumble over several drops or steps. Water always flows downhill. It takes just the right combination of flowing water and dramatic landforms to make a spectacular waterfall. Word Wise A rapid is a section of a river where the water flows swiftly and turbulently over a rocky surface. but it is not considered a waterfall.

瀑布是怎么形成的?瀑布由两部分组成:溪流或河流和陡峭的土地。 水流过斜坡、壁架或悬崖。 有些瀑布，叫做瀑布，垂直地从空中落下。 另一些叫做瀑布，在几滴或几级台阶上翻滚。 水总是往低处流。 它需要流动的水和引人注目的地貌的恰当组合，才能形成壮观的瀑布。 急流是河流的一段，水流在岩石表面上迅速而湍流地流动。 但它不被认为是瀑布。

Vertical Drop-Offs True falls require land that drops away suddenly, such as a steep slope or cliff. These landforms can form in many ways. Uneven Erosion Different types of rock wear away at different rates In some places very hard rock lies next to or on top of softer rock. Wind and water wear away the soft rock more quickly. The hard rock remains forming a steep cliff called a scarp. Mountains Where the large plates of Earth's crust meet, the edges can collide and push upward to form mountains with steep slopes and canyons. Faults Faults are enormous cracks in Earth's surface. The rock on one side of a fault can push up or slide down as plates move, forming a steep slope or cliff.

真正的瀑布需要地面突然下降，比如陡坡或悬崖。 这些地貌可以以多种方式形成。 不均匀侵蚀不同类型的岩石以不同的速度磨损。在一些地方，非常坚硬的岩石位于较软的岩石旁边或上面。 风和水更快地磨损软岩石。 坚硬的岩石残留下来形成了一个陡峭的悬崖，叫做陡壁。 在地壳的大板块相遇的地方，边缘会碰撞并向上推动，形成山坡陡峭的山脉和峡谷。 断层断层是地球表面的巨大裂缝。 当板块移动时，断层一侧的岩石可以向上推或向下滑动，形成陡峭的斜坡或悬崖。

Volcanic Flows When a volcano erupts, thick, slow-flowing lava may move across the land. These lava flows can form tall piles. After the lava cools the rock often cracks apart and falls away in big chunks, leaving behind slopes and cliffs. Glacial Valleys Glaciers are enormous rivers of ice that creep downhill. They bulldoze huge U-shaped valleys with high steep sides. Sea Cliffs Ocean waves wear away soft rock, forming tall sea cliffs. Travertine Cliffs Travertine is a kind of rock that forms from minerals dissolved in water. When water carrying certain minerals flows across a surface some of the minerals get left behind. Over time the minerals build up, forming a sloped shelf of travertine rock.

火山流动当火山爆发时，厚厚的、缓慢流动的熔岩可能在陆地上移动。 这些熔岩流可以形成高高的堆。 熔岩冷却后，岩石通常会破裂成大块下落，留下斜坡和悬崖。 冰川是向下坡蔓延的巨大冰河。 他们推平了巨大的u型山谷，山谷的两边都是高陡的。 海浪冲刷柔软的岩石，形成高耸的海崖。 石灰华是一种由溶解在水中的矿物质形成的岩石。 当携带某些矿物质的水流经地表时，有些矿物质会被留下。 随着时间的推移，矿物逐渐堆积，形成了石灰华岩石的倾斜架子。

Just Add Water Once a steep or sloping landform is present flowing water goes to work. A stream flows down a slope. Or it might flow over a drop, such as a fault or a boulder. The flowing water begins to wear away the underlying rock. The softer layers of rock wear away faster than the harder ones. If the top layer is the hardest, a ledge forms. The water flows faster as it drops over the ledge. This faster- moving water erodes the softer rock at the bottom of the drop even more. As the slope gets steeper, the water flows even faster. The water erodes the drop even more. As this process continues, a large waterfall eventually forms. Over time, the waterfall shifts upstream due to erosion.

只要加水，一旦出现陡峭或倾斜的地形，流动的水就会发挥作用。 一条小溪沿着斜坡流下来。 或者它可能流过一滴，如断层或巨石。 流水开始侵蚀下面的岩石。 较软的岩石层比较硬的磨损得更快。 如果最上面的一层是最硬的，就会形成一个壁架。 当水流过岩壁时，水流得更快。 这种快速流动的水对水滴底部较软的岩石的侵蚀更大。 坡度越陡，水流越快。 水对水滴的侵蚀更大。 随着这个过程的继续，最终形成了一个巨大的瀑布。 随着时间的推移，瀑布因侵蚀而向上游移动。