The seething spectacle of Niagara, really two falls in one, has few rivals for its dual traits of beauty and sheer overwhelming power. The Niagara River is not very long. From its source, the outlet of Lake Erie, to its end in Lake Ontario, it flows a total distance of only about 35 miles (55 kilometers). Yet its name is known far and wide. About halfway along its short northward course the river, which carries the overflow of four of the five Great Lakes, plunges over a precipice in the paired cascades of Niagara Falls.
A thunderous, unending roar greets visitors long before the falls come into view. But nothing can quite prepare them for the sight of the two seething sheets of water hurtling into the gorge on either side of Goat Island. To the north of the island is the long, nearly straight line of the American Falls, spanning a distance of about 1,060 feet (325 meters). To the south and west, on the side of Canada of the river is the gracefully curving arc of Horseshoe Falls, with the length of its crest measuring slightly more than 2,200 feet (670 meters). Both cascades drop a total of 180 feet (55 meters).
Although the falls may seem both very old and quite unchanging, they actually are neither. Niagara Falls came into being only as the Ice Age drew to a close some 10,000 years ago. As the enormous ice cap that had covered much of northern North America wasted away, the Great Lakes gradually assumed their present form and drainage pattern. The lakes once emptied into the Mississippi River. But as the ice receded to the north, they eventually found their present outlet to the sea by way of Lake Ontario and the St. Lawrence River.
Besides being the easternmost of the Great Lakes, Ontario is also the closest to sea level. About 7 miles (11 kilometers) north of Niagara Falls, the surface of the land drops abruptly in a steep escarpment. And originally it was there that the Niagara River made its breathtaking plunge en route to Lake Ontario. But the falls did not remain at the edge of the cliff for long. The escarpment is capped by a thick, nearly horizontal layer of extremely hard dolomite (a type of limestone). Beneath the dolomite are layers of shale, sandstone, and other much more easily eroded rocks. As water poured over the precipice, churning up fallen rocks in the riverbed below, the softer underlying layers were worn away, leaving an overhanging cornice of dolomite. But eventually tensions in the dolomite became so great that huge blocks of it came crashing down.
Century by century, as undercutting of the dolomite continued, the falls receded upstream, leaving the deep Niagara Gorge in their wake. It is believed that they reached more or less their present location about 600 years ago, when the obstruction of Goat Island divided them into two separate cataracts.
Because the river is both wider and deeper on the southwestern side of the island, erosion proceeded much more rapidly there, and carved the deep, curving indentation of Horse-shoe Falls. (According to one estimate, Horseshoe Falls have receded more than 1,000 feet, or 300 meters, since the French explorer Louis Hennepin first viewed them in 1678.) With less than 10 percent of the river’s flow channeled over them, the American Falls are much more stable, forming a long, more or less straight line.
Parks have been established on both sides of Niagara. The best known of several bridges that span the gorge is Rainbow Bridge, just below the falls, which affords fine views of the rainbows that form on the falls’ towering clouds of spray. Other favored vantage points include scenic walkways in the parks (the most dramatic views are from the Canadian side), as well as nearby observation towers. The falls can also be inspected from helicopters, but the most unusual views are from boats that ply the turbulent water in the gorge below the falls. The boats have traditionally been named Maid of the Mist, commemorating the legend of an Indian girl who is said to have gone over Niagara in a canoe, and whose ghostly image sometimes appears in the spray.
Because the Niagara River drops a total of 326 feet (99 meters) between lakes Erie and Ontario, its huge volume of flow has long been used for generating power. Today water is diverted from the river above the falls and channeled through mammoth ducts to the generating plants downstream. Thus, though few are aware of it, only about half as much water spills over the falls as did in the past.
The lessened flow has slowed the rate of erosion, as have elaborate control structures built above the falls. The cataracts are still receding, although very slowly now, and experts predict that they will remain in their present general location for hundreds of years to come.