Glacial activity and erosion helped create Niagara Falls, a spectacular natural wonder that attracts millions of visitors yearly. First-time tourists may be surprised to learn that Niagara consists of three separate falls: American and Bridal Veil Falls near Niagara Falls, NY, and Canadian Horseshoe Falls close to Ontario, Canada.

American Falls, with a width of 259 meters (850 feet), is much wider than Bridal Veil Falls, whose width is 15.2 meters (50 feet). Canadian Horseshoe Falls is the widest measuring 670.6 meters (2,200 feet). It's also the tallest with a vertical drop of 57.3 meters (188 feet). The other two falls only drop 54.9 meters (180 feet). Water from the Niagara River flows over the Niagara Escarpment's edge to create the three falls. This escarpment, an area where elevation changes suddenly, stretches from Ontario through New York and several other states.

The area where Niagara Falls sits was under a mile of glacial ice during the last ice age. When the ice retreated about 16,000 years ago, water from the Great Lakes looked for a low path over which it could flow. About 12,000 years ago, that water found a path through the Niagara Escarpment and began to carve out the Niagara River. When you visit the area, you'll see the water flowing over the escarpment's edge at a rate of 169,901.0 cubic liters (6 million cubic feet) per minute.

Niagara falls was 11.23 kilometers (7 miles) further downstream 12,000 years ago than it is today. Continuous water flow eroded Niagara's rocks, causing the falls to move upstream. This erosion, which created the Niagara Gorge, continues today and moves the falls back at an estimated 0.3 meters (1 foot) per year.