Niagara Fall
| Niagara Falls | |
|---|---|
 | |
| Location | Border of Ontario, Canada, and New York, United States |
| Coordinates | 43.0799°N 79.0747°W |
| Type | Cataract |
| Total height | 167 ft (51 m) |
| Number of drops | 3 |
| Watercourse | Niagara River |
| Average flow rate | 85,000 cu ft/s (2,400 m3/s) |
Niagara Falls (/naɪˈæɡrə/) 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 New York state. 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 lies on the border of the United States and Canada[1] with the American Falls entirely on the United States' side, separated by Goat Island. The smaller Bridal Veil Falls are also on the United States' side, separated from the other waterfalls by Luna Island.
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 that has a vertical drop of more than 165 feet (50 m). During peak daytime tourist hours, more than six million cubic feet (168,000 m3) of water goes over the crest of the falls every minute.[2] Horseshoe Falls is the most powerful waterfall in North America, as measured by flow rate.
The falls are 17 miles (27 km) north-northwest of Buffalo, New York, and 75 miles (121 km) south-southeast of Toronto, between the twin cities of Niagara Falls, Ontario, and Niagara Falls, New York. Niagara Falls was 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.
Niagara Falls is famed both for its beauty and as a valuable source of hydroelectric power. Balancing 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 188 feet (57 m), while the height of the American Falls varies between 70 and 100 feet (21 and 30 m) because of the presence of giant boulders at its base. The larger Horseshoe Falls are about 2,600 feet (790 m) wide, while the American Falls are 1,060 feet (320 m) wide. The distance between the American extremity of the Niagara Falls and the Canadian extremity is 3,409 feet (1,039 m).
The peak flow over Horseshoe Falls was recorded at 225,000 cubic feet (6,400 m3) per second. The average annual flow rate is 85,000 cubic feet (2,400 m3) per second. 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 100,000 cubic feet (2,800 m3) 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 – the International Control Dam – 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 50,000 cubic feet (1,400 m3) per second. Water diversion is regulated by the 1950 Niagara Treaty and is administered by the International Niagara Board of Control (IJC).
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 1 foot (0.30 m) per year, down from a historical average of 3 feet (0.91 m) per year. It is estimated that 50,000 years from now, even at this reduced rate of erosion, the remaining 20 miles (32 km) to Lake Erie will have been undermined and the falls will cease to exist
Geology
The features that became Niagara Falls were created by the Wisconsin glaciation about 10,000 years ago. The same forces also created the North American Great Lakes and the Niagara River. All were dug by a continental ice sheet that drove through the area, deepening some river channels to form lakes, and damming others with debris.[9] Scientists argue there is an old valley, St David's Buried Gorge, buried by glacial drift, at the approximate location of the present Welland Canal.
When the ice melted, the upper Great Lakes emptied into the Niagara River, which followed the rearranged topography across the Niagara Escarpment. In time, the river cut a gorge through the north-facing cliff, or cuesta. Because of the interactions of three major rock formations, the rocky bed did not erode evenly. The top rock formation was composed of erosion-resistant limestone and Lockport dolostone. That hard layer of stone eroded more slowly than the underlying materials. The aerial photo on the right clearly shows the hard caprock, the Lockport Formation (Middle Silurian), which underlies the rapids above the falls, and approximately the upper third of the high gorge wall.
