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Niagara Falls (, Cayuga: ''Gahnawehtaˀ'' or ''Tgahnawęhtaˀ'') is the collective name for three waterfalls that straddle the international border between Canada and the United States; more specifically, between the province of Ontario and the state of New York. They form the southern end of the Niagara Gorge. From largest to smallest, the three waterfalls are the Horseshoe Falls, the American Falls and the Bridal Veil Falls. The Horseshoe Falls lie mostly on the Canadian side and the American Falls entirely on the American side, separated by Goat Island. The smaller Bridal Veil Falls are also located on the American side, separated from the other waterfalls by Luna Island. The international boundary line was originally drawn through Horseshoe Falls in 1819, but the boundary has long been in dispute due to natural erosion and construction.〔Staff report (October 25, 1905). Niagara boundary issue. ''Boston Evening Transcript''〕 Located on the Niagara River, which drains Lake Erie into Lake Ontario, the combined falls form the highest flow rate of any waterfall in the world, with a vertical drop of more than 165 feet (50 m). Horseshoe Falls is the most powerful waterfall in North America, as measured by vertical height and also by flow rate.〔(【引用サイトリンク】title=City Profile for Niagara Falls, Ontario )〕 The falls are located north-northwest of Buffalo, New York and south-southeast of Toronto, between the twin cities of Niagara Falls, Ontario, and Niagara Falls, New York. Niagara Falls were formed when glaciers receded at the end of the Wisconsin glaciation (the last ice age), and water from the newly formed Great Lakes carved a path through the Niagara Escarpment en route to the Atlantic Ocean. While not exceptionally high, the Niagara Falls are very wide. More than six million cubic feet (168,000 m3) of water falls over the crest line every minute in high flow,〔(【引用サイトリンク】 Falls Facts (Trivia) – Niagara Parks, Niagara Falls, Ontario, Canada )〕 and almost four million cubic feet (110,000 m3) on average. The Niagara Falls are renowned both for their beauty and as a valuable source of hydroelectric power. Managing the balance between recreational, commercial, and industrial uses has been a challenge for the stewards of the falls since the 19th century. ==Characteristics== The Horseshoe Falls drop about ,〔(''Niagara Falls Geology Facts & Figures.'' ) Niagara Parks, Government of Ontario, Canada. Retrieved 26 July 2014.〕 while the height of the American Falls varies between because of the presence of giant boulders at its base. The larger Horseshoe Falls are about wide, while the American Falls are wide. The distance between the American extremity of the Niagara Falls and the Canadian extremity is . The volume of water approaching the falls during peak flow season may sometimes be as much as per second.〔(【引用サイトリンク】 Niagara Falls History of Power – Historical and engineering data on the U.S. and Canadian power stations )〕 The average annual flow rate is per second.〔(【引用サイトリンク】 Niagara Falls - World Waterfall Database )〕 Since the flow is a direct function of the Lake Erie water elevation, it typically peaks in late spring or early summer. During the summer months, at least per second of water traverses the falls, some 90% of which goes over the Horseshoe Falls, while the balance is diverted to hydroelectric facilities. This is accomplished by employing a weir with movable gates upstream from the Horseshoe Falls. The falls' flow is further halved at night, and, during the low tourist season in the winter, remains a minimum of per second. Water diversion is regulated by the 1950 Niagara Treaty and is administered by the International Niagara Board of Control (IJC).〔(【引用サイトリンク】 IJC – International Niagara Board of Control )〕 The verdant green colour of the water flowing over the Niagara Falls is a byproduct of the estimated 60 tonnes/minute of dissolved salts and "rock flour" (very finely ground rock) generated by the erosive force of the Niagara River itself. The current rate of erosion is approximately per year down from a historical average of per year. It is estimated that 50,000 years from now, even at this reduced rate of erosion, the remaining to Lake Erie will have been undermined and the falls will cease to exist.〔(【引用サイトリンク】url=http://www.niagaraparks.com/media/geology-facts-figures.html )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Niagara Falls」の詳細全文を読む スポンサード リンク
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