Niagara Falls is a natural geological feature, a product of immense prehistoric forces. It stands as a powerful landmark situated on the border between the United States and Canada. While human engineering manages the flow of the Niagara River, the fundamental structure of the falls and the gorge are entirely the result of natural processes. This spectacle of three waterfalls—Horseshoe Falls, American Falls, and Bridal Veil Falls—is a testament to the slow, persistent power of water cutting through the Earth’s crust.
The Natural Forces That Created the Falls
The formation of Niagara Falls is directly linked to the massive glacial events of the last ice age, known as the Wisconsin Glaciation, which ended approximately 10,000 years ago. Glaciers over a mile thick carved out the Great Lakes basin, and when they melted, the water began to flow over a large geological formation called the Niagara Escarpment. This escarpment is not a fault line but a cuesta, a ridge of rock layers tilted slightly downward, which provided the initial drop-off for the falls.
The unique structure of the escarpment allows the cataract to persist through a process of differential erosion. The top layer of rock, which forms the riverbed and the crest of the falls, is a hard, erosion-resistant caprock composed of Lockport Dolomite, a Middle Silurian rock. Beneath this durable layer lies the softer, more easily worn away Rochester Shale. The Niagara River water erodes this softer shale layer, undermining the dolomite caprock above it.
As the softer shale is worn away, the hard dolomite caprock loses its support and eventually collapses in large blocks, causing the falls to slowly retreat upstream. This process has caused the falls to move approximately 11 kilometers from its original position at the edge of the escarpment over thousands of years. Before human intervention, the average rate of recession for the Horseshoe Falls was historically measured at up to 0.9 to 1.6 meters per year.
Major Human Interventions
The immense power of the falls has been harnessed for over a century through significant engineering projects designed to generate hydroelectric power. This large-scale diversion of the Niagara River’s flow is the primary reason many people mistakenly believe the falls are man-made. The first step in this process involves the International Control Structure (ICS), a gated weir built upstream of the falls that regulates the amount of water continuing over the crest.
The water is diverted into a system of massive underground infrastructure, including tunnels and intake pipes, before it ever reaches the brink of the falls. For instance, on the Canadian side, three diversion tunnels carry water beneath the city of Niagara Falls, Ontario, to the Sir Adam Beck hydroelectric complex. On the American side, similar tunnels direct water to the Robert Moses Power Plant in Lewiston, New York.
These tunnels feed the water into large forebays and reservoirs, such as the 300-hectare reservoir behind the Sir Adam Beck complex, which store water for pumped-storage power generation. This infrastructure allows power authorities on both sides of the border to tap into the river’s potential, generating electricity for millions of homes.
Controlling Erosion and Water Flow
Beyond the diversion for energy, other major structures were built directly into the riverbed to manage the falls’ physical integrity. The International Control Structure, constructed in 1954, serves the dual purpose of both diverting water for power and preserving the falls’ appearance. It consists of 18 sluice gates and extends partway across the river from the Canadian shore upstream of the Horseshoe Falls.
This control structure allows engineers to evenly distribute the water flow across the crest of the falls, which is necessary to prevent excessive erosion in one specific area. The structure ensures that a minimum flow is maintained over the falls as stipulated by the 1950 Niagara Treaty between the U.S. and Canada. The treaty mandates a minimum flow of 2,800 cubic meters per second during daylight hours in the tourist season to maintain an “unbroken curtain of water”.
During the night and the winter off-season, the flow over the falls is permitted to drop to 1,400 cubic meters per second, allowing more water to be diverted for maximum power generation. This active management of the water flow has dramatically slowed the natural rate of recession to a current average of about 30 centimeters (12 inches) per year.