英語聽力文摘652 尼亞加拉大瀑布正在慢慢消失
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Niagara Falls has been a famous honeymoon 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 erode, the falls are moving upstream, so they will one day disappear into Lake Erie.
Like all waterfalls, Niagara erodes 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 collapse 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 suite 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.
尼亞加拉大瀑布正在慢慢消失!
一百多年來，尼亞加拉大瀑布一直是聞名的蜜月旅行圣地：許多新婚夫婦對(duì)它的情有獨(dú)鐘勝過對(duì)彼此的忠誠。
瀑布是何時(shí)形成的
大瀑布形成于更新世時(shí)期晚期，距今一萬兩千年左右，自那以后大瀑布一直遭受外力的侵蝕。隨著侵蝕的繼續(xù)，大瀑布也在一天天地往上游移動(dòng)，因此，終有一天，大瀑布將消失在伊利湖。
像所有的瀑布一樣，尼亞加拉大瀑布也在遭受侵蝕，因?yàn)樗鞑粩嗟啬p懸崖底部較軟的石頭，而那里正是瀑布下方湍流池形成的地方。因?yàn)榍治g對(duì)懸崖底部影響較大，舊有的懸崖面在侵蝕的作用下倒塌，新的懸崖面形成并將逐漸往上游移動(dòng)。侵蝕率取決于許多因素，諸如經(jīng)過懸崖面的水流量、瀑布的高度以及構(gòu)成瀑布底部的巖石的類型。
水流量
尼亞加拉大瀑布水流量非常大。事實(shí)上，世界上五分之一的淡水源自蘇比利爾湖、休倫湖、密歇根胡和艾爾湖，它們流經(jīng)大瀑布并最終進(jìn)入安大略湖。尼亞加拉大瀑布是世界上第二大瀑布。
在你取消那配備著心形浴缸的蜜月套房前，一定要記住：在過去的12,000年，大瀑布已經(jīng)往上游移動(dòng)了七英里，按照這個(gè)速度計(jì)算，再過不到23,000年，它就要永遠(yuǎn)地消失在伊利湖了。在這之前，你有足夠的時(shí)間可以進(jìn)行一次蜜月之旅，即便是第二次蜜月之旅也來得及。
