Rate of Recession of Niagara Falls
Rate of Recession of Niagara Falls
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尼亚加拉大瀑布的衰退速度
DOI：
10.1086/278833
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发表时间：
1907
期刊：
影响因子：
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通讯作者：
D. W. Johnson
中科院分区：
文献类型：
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作者：
D. W. Johnson
542美国博物学家[第一卷XLI向上游后退，瀑布下方的峡谷是这次衰退的结果，通过足够准确的观察，将有可能确定衰退的速度。然后，他讨论了计算衰退速度必须基于的数据，包括对1842年、1875年、1886年、1890年和1905年瀑布顶线的调查；以及1827年的相机-光感素描。在考虑了不同调查和草图的相对准确性，并将结果放在一起后，作者得出结论，马蹄形瀑布的衰退是渐进的，而美国瀑布的衰退速度要慢得多。这些变化通过对比鲜明的照片和素描表现出来，这些照片和素描是从相同的角度制作的，但相隔多年。关于这项研究的定量结果，作者指出，可以用不同的方式处理现有的数据，并使其产生截然不同的结果。不和谐的部分原因是调查中的不准确，其中一些是不可避免的；部分是因为石灰岩顶部剥离的速度必然是不规律的。因此，不应把太多信心寄托在衰退速度的精确数学表达式上。然而，总的来说，证据证明，马蹄形瀑布在1842年至1905年的63年间，每年衰退约5英尺，误差可能不超过1英尺；而在1827年至1905年的78年间，美国瀑布的衰退每年不到3英寸。本报告没有考虑从刘易斯顿附近以前的位置下跌的总衰退时间，但作者简要指出了在估计这一时间时必须考虑的许多可变因素中的一些因素。W.Carvel Hall关于瀑布顶线的最新调查的简短报告附在论文之后。
542 THE AMERICAN NATURALIST[VoL. XLI receding upstream, that the gorge below the falls is the result of this recession, and that it would be possible, by sufficiently accurate observations, to determine the rate of recession. He then discusses the data upon which computations of the rate of recession must be based, consisting of surveys of the crest-line of the falls made in 1842, 1875, 1886, 1890, and in 1905; and camera-lucida sketches made in 1827. After considering the relative accuracy of the different surveys and sketches, and platting the results together, the author concludes that a gradual recession of the Horseshoe Falls is demonstrated, while a much slower rate of recession is indicated for the American Falls. These changes are strikingly represented by contrasted photographs and sketches made from the same view-point, but many years apart. Concerning quantitative results of the study, the author points out that the available data may be treated in a variety of ways, and made to yield widely divergent results. The lack of harmony is due iin part to inaccuracies in the surveys, some of which are unavoidable; and in part to the fact that the rate at which the limestone crest breaks away is necessarily irregular. Too much confidence should not, therefore, be placed in exact mathematical expressions of the rate of recession. In general, however, the evidence proves a recession of about 5 feet a year with a possible error of not more than 1 foot, for the Horseshoe Falls, in the sixty-three years from 1842 to 1905; and a recession of less than 3 inches a year for the American Falls, in the seventy-eight years from 1827 to 1905. The time consulme (1 in the total recession of the falls from their former position near Lewiston is not considered in this report, except that the author briefly notes some of the many variable factors which must be taken into account in estimating such time. A short report by W. Carvel Hall on the latest survey of the crest line of the falls is appended to the paper.