英语听力文摘 English Digest 652 尼亚加拉大瀑布正在慢慢消失

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　　Niagara Falls has been a famous honeymoon¹ spot for over a hundred years: some honeymooners have been more faithful to it than to each other.

　　When The Falls Formed

　　Since the falls were formed during the late Pleistocene period, about twelve thousand years ago, they have been subject to the force of erosion. As they erode², the falls are moving upstream, so they will one day disappear into Lake Erie.

　　Like all waterfalls, Niagara erodes³ because water wears away the softer rock at the base of the cliff, where a turbulent pool forms below the waterfall. Because erosion affects the base of the cliff, the old cliff face will collapse⁴ and the new edge will be slightly upstream. The rate of erosion depends on factors like the volume of water going over the edge, the height of the drop, and the type of rocks that make up the base of the waterfall.

　　Water Volume

　　At Niagara, the volume of water is very high. In fact, one-fifth of the world’s fresh water empties from the Great Lakes Superior, Huron, Michigan, and Erie over the falls into Lake Ontario. Niagara is the second largest waterfall in the world.

　　Before you cancel your honeymoon suite⁵ with the heart-shaped tub, keep in mind that in the past 12,000 years the falls have moved about seven miles upstream and, at this rate, they will disappear into Lake Erie in just under 23,000 years. Enough time to visit on a honeymoon–and even a second honeymoon.

　　尼亚加拉大瀑布正在慢慢消失！

　　一百多年来，尼亚加拉大瀑布一直是闻名的蜜月旅行圣地：许多新婚夫妇对它的情有独钟胜过对彼此的忠诚。

　　瀑布是何时形成的

　　大瀑布形成于更新世时期晚期，距今一万两千年左右，自那以后大瀑布一直遭受外力的侵蚀。随着侵蚀的继续，大瀑布也在一天天地往上游移动，因此，终有一天，大瀑布将消失在伊利湖。

　　像所有的瀑布一样，尼亚加拉大瀑布也在遭受侵蚀，因为水流不断地磨损悬崖底部较软的石头，而那里正是瀑布下方湍流池形成的地方。因为侵蚀对悬崖底部影响较大，旧有的悬崖面在侵蚀的作用下倒塌，新的悬崖面形成并将逐渐往上游移动。侵蚀率取决于许多因素，诸如经过悬崖面的水流量、瀑布的高度以及构成瀑布底部的岩石的类型。

　　水流量

　　尼亚加拉大瀑布水流量非常大。事实上，世界上五分之一的淡水源自苏比利尔湖、休伦湖、密歇根胡和艾尔湖，它们流经大瀑布并最终进入安大略湖。尼亚加拉大瀑布是世界上第二大瀑布。

　　在你取消那配备着心形浴缸的蜜月套房前，一定要记住：在过去的12,000年，大瀑布已经往上游移动了七英里，按照这个速度计算，再过不到23,000年，它就要永远地消失在伊利湖了。在这之前，你有足够的时间可以进行一次蜜月之旅，即便是第二次蜜月之旅也来得及。

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