Niagara Falls

Niagara Falls is a set of massive waterfalls located on the Niagara River in eastern North America, on the border between the United States and Canada. Three separate waterfalls constitute Niagara Falls: the Horseshoe Falls (Canadian Falls), the American Falls, and the smaller, adjacent Bridal Veil Falls. The falls are located 16 miles from the U.S. city of Buffalo and 43 miles from the Canadian city of Toronto. The falls formed after the receding of the glaciers of the most recent Ice Age, as 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. With more than six-million cubic feet of water falling over the crestline every minute in high flow, and almost four million cubic feet on average, they constitute the most powerful waterfall in North America.

Not renowned only for their beauty, the falls are a valuable source of hydroelectric power for both Ontario and New York. Preserving this natural wonder from commercial overdevelopment while allowing for the needs of the area's people has been a challenging project for environmental preservationists since the nineteenth century. A popular tourist site for over a century, the falls are shared by the twin cities of Niagara Falls, Ontario and Niagara Falls, New York. Some 20 million visitors are expected to visit the falls in 2007, with the annual rate increasing in 2009 to over 28 million tourists a year.

Formation

The historical roots of Niagara Falls lie in the Wisconsin glaciation, which ended around tren thousand years ago. The North American Great Lakes and the Niagara River are effects of this last continental ice sheet, an enormous glacier that crept across the area from eastern Canada. The glacier drove through the area like a giant bulldozer, grinding up rocks and soil, moving them around, and deepening some river channels to make lakes. It dammed others with debris, forcing these rivers to make new channels.It is thought that there is an old valley, buried by glacial drift, at the approximate location of the present Welland Canal.

After the ice melted, drainage from the upper Great Lakes became the present-day Niagara River, which could not follow the old filled valley, so it found the lowest outlet on the rearranged topography. In time the river cut a gorge across the Niagara Escarpment, the north facing cliff or cuesta formed by erosion of the southwardly dipping (tilted) and resistant Lockport formation between Lake Erie and Lake Ontario. In doing so it exposed old marine rocks that are much older than the geologically recent glaciation. Three major formations are exposed in the gorge that was cut by the Niagara River.

When the newly established river encountered the erosion-resistant Lockport dolostone, the hard layer eroded much more slowly than the underlying softer rocks. The aerial photo 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. It is composed of very dense, hard, and very strong limestone and dolostone.

Immediately below, comprising about two thirds of the cliff, is the weaker, softer, and more crumbly and sloping Rochester Formation (Lower Silurian). It is mainly shale, though it has some thin limestone layers, and contains large quantities of fossils. Because it erodes more easily, the river has undercut the hard cap rock and created the falls.

Submerged in the river in the lower valley, hidden from view, is the Queenston Formation (Upper Ordovician), which is composed of shales and fine sandstones. All three formations were laid down in an ancient sea, and their differences of character derive from changing conditions within that sea.

The original Niagara Falls were near the sites of present-day [[Queenston, Ontario, Canada, and Lewiston, New York, but erosion of their crest has caused the waterfalls to retreat several miles southward. Just upstream from the Falls' current location, Goat Island splits the course of the Niagara River, resulting in the separation of the Canadian Horseshoe Falls to the west from the American and Bridal Veil Falls to the east. Although erosion and recession have been slowed in this century by engineering, the falls will eventually recede far enough to drain most of Lake Erie, the bottom of which is higher than the bottom of the falls. Engineers are working to reduce the rate of erosion to retard this event as long as possible.

The Canadian Horseshoe Falls drop about 170 feet, although the American Falls have a clear drop of only 70 feet before reaching a jumble of fallen rocks which were deposited by a massive rock slide in 1954. The larger Canadian Horseshoe Falls are about 2,600 feet wide, while the American Falls are 1,060 feet wide. The volume of water approaching the Falls during peak flow season is 202,000 cubic feet per second.By comparison Africa's spectacular Victoria Falls has over 19 million cubic feet of water falling over its crestline each minute in the wet season, and spray from this rises several hundreds of feet into the air because of the incredible force of the falling water.

During the summer months, when maximum diversion of water for hydroelectric power occurs, 100,000 cubic feet per second of water actually traverses the falls, some ninety percent of which goes over the Horseshoe Falls. This volume is further halved at night, when most of the diversion to hydroelectric facilities occurs.

Credited to new world encyclopedia and flickr:Jenny Cohn,Harry1125,Wolfgang Staudt,