The Niagara Falls started some 10,000 years ago in the Wisconsin glaciation period. Both the North American Great Lakes and the Niagara River are the results of this last continental ice sheet, a huge glacier that swept across the area from eastern Canada. During the birth of Niagara Falls the glacier ripped through the area like a giant bulldozer, destroying rocks and soil, tossing them around, and turning some river channels into lakes. It dammed other channels with debris, forcing these rivers to divert and make new channels. It's believed is an ancient valley, buried by glacial drift, about where, now, the Welland Canal is located.
Once the ice melted, drainage from the upper Great Lakes became the Niagara River, which could not follow the now filled valley, so it found the deepest outlet on the new landscape. Over the years the river cut a gorge across the Niagara Escarpment, the north facing cliff of the southern tilted and resistant Lockport formation between Lake Erie and Lake Ontario. As it moved through there it exposed old marine rocks that are quite a bit older than the comparatively recent glaciation. There are three major formations that were exposed in the gorge that was cut by the Niagara River.
The Falls plunge about 170 feet (52 meters), however, the American Falls have a only a drop of 70 feet (21 meters) before hitting a pile of fallen rocks which were deposited by a massive rock slide in 1954. The bigger Canadian Falls are about 2,600 feet (792 meters) wide, while the American Falls are 1,060 feet (323 meters) wide. The amount of water approaching the Falls during peak flow season is 202,000 feet (5,720 meters). However in the summer months, when the largest diversion of water for hydroelectric power occurs, 100,000 feet (2,832 meters) of water actually spills over the Falls, and about 90% of that goes over the Horseshoe Falls. This volume is further cut in half at night, when most of the water delivery to hydroelectric facilities occurs.
Although erosion has been drastically reduced in this century by modern day techniques, the falls will eventually recede far enough to drain most of Lake Erie, since the bottom of the lake is higher than the bottom of the falls. Engineers are working to reduce the rate of erosion to delay this event as long as possible. Originally the Niagara Falls were located near the site of Lewiston, New York, and Queenston, Ontario, but erosion at the top has caused the waterfalls to move some miles south. Just upstream from their current location, Goat Island causes a split in the the course of the Niagara River, resulting in separating the Horseshoe Falls in the west from the American and Bridal Veil Falls in the east. "