World+Geography+Understanding+a+Changing+World

Niagara Falls

Straddling the border between Canada and the United States, Niagara Falls is one of the world's most famous and most powerful waterfalls, transporting nearly 2.7 billion gallons of water an hour pouring over a sheer drop of up to 188 feet. Although hundreds of waterfalls around the world are taller, this combination of volume and height has long made Niagara Falls an awe-inspiring tourist destination as well as a major source of hydroelectric power. The Niagara River, of which the falls are a part, drains four of the five Great Lakes and connects Lake Erie with Lake Ontario.

Niagara Falls actually comprises three separate waterfalls: Horseshoe Falls on the northern (Canadian) side of the river, and American Falls and Bridal Veil Falls on the southern (U.S.) side. Horseshoe Falls averages 188 feet high and is 2,200 feet wide; American Falls ranges from 70 feet to 110 feet high and is 850 feet wide. Bridal Veil Falls is just 50 feet wide and lies between the two larger falls, separated from them by Goat and Luna Islands, which divert the Niagara River's flow into three channels. Combined, the falls stretch more than 3,000 feet across, separating the river's upper and lower stretches. The Niagara River's deepest pointâ€”170 feetâ€”is directly below the falls, where the sheer force of the water has eroded a massive plunge pool over thousands of years.

Glacial meltwaters formed the falls about 12,300 years ago, near the end of the last Ice Age. At that time, a sheet of ice well over a mile thick covered what is now southern Ontario province in Canada. As it began to melt, this ice formed the Great Lakes and carved their eastern outlet to the Atlantic, via Lake Erie, the Niagara River, Lake Ontario, and the St. Lawrence River. Initially, five separate water courses connected Lakes Erie and Ontario. These eventually converged at the Niagara Escarpment, a cliff seven miles downstream of the present falls, where Lewiston, New York and Queenston, Ontario are today. Erosion at the falls was so great that it wore away the underlying rock at a rate of up to six feet per year, steadily moving the falls upstream to their present location.

The force of the falling water (280 tons at American and Bridal Veil falls, and 2,509 tons at Horseshoe Falls) continues to erode the Niagara Escarpment, though at a much slower rate due to the diversion of water for hydroelectric power. (Historically, up to 5.5 billion gallons of water plunged from atop the falls every hour.) The top of the escarpment consists of dolostone, a hard sedimentary rock formed from layers of sediment laid down by an ancient, tropical sea more than 400 million years ago. Below this hard rock "cap" are softer layers of shale, sandstone, and limestone that wear away more rapidly. Erosion of these softer rocks undercuts the dolostone cap, which periodically collapses into the gorge below.

This process was altered when the U.S. and Canadian governments signed the 1950 Niagara Treaty, which determined how much water could be diverted for generating hydroelectric power. Niagara Falls had been a source of electricity since 1895, when the world's first large-scale hydropower generation project opened there. However, the 1950 agreement greatly increased capacity. The treaty requires that water flow over Niagara Falls must be maintained at 100,000 cubic feet per second (cfs) during daylight hours in the tourist season (April 1 through October 31). Outside this time frame, flow must be at least 50,000 cfs. Water in excess of these amounts can be diverted for drinking water, municipal sewage systems, andâ€”most significantlyâ€”power generation. Today Niagara Falls can produce more than 4 million kilowatts of electricity, and more than 1 million Canadians and Americans rely upon their waters in some way.

Since the 1950 hydropower diversion, the annual rate of erosion at Horseshoe Falls has slowed from just over four feet to just over two feet. American Falls are now stabilized by a mass of cables and bolts that has virtually eliminated erosion. In addition, diversions have lowered water levels in the Niagara River by about 16 feet.

Terri Nichols

MLA Citation Nichols, Terri. "Niagara Falls." World Geography: Understanding a Changing World. ABC-CLIO, 2015. Web. 15 Sept. 2015.