Niagara Falls is a collective name for three waterfalls—Horseshoe Falls, American Falls, and Bridal Veil Falls—that straddle the international border between the United States and Canada. While the falls’ existence and scale are the result of natural geological forces over millennia, human intervention has profoundly influenced the river’s flow and physical appearance. The modern spectacle is a complex blend of natural history and extensive engineering.
The Geological Birth of Niagara Falls
The origin of Niagara Falls lies in the powerful force of the last major ice age, the Wisconsin Glaciation. Approximately 12,000 years ago, as massive ice sheets retreated, they left behind a rearranged landscape and enormous quantities of meltwater. This meltwater filled the basins carved by the glaciers, forming the Great Lakes system.
The Niagara River emerged as the channel draining the upper Great Lakes (primarily Lake Erie) northward into Lake Ontario. The river’s path crossed the Niagara Escarpment, a prominent north-facing cliff composed of ancient rock layers. The initial waterfall began at the escarpment near present-day Queenston, New York, and Lewiston, Ontario.
The distinct structure of the falls is a result of differential erosion between rock layers. The top layer, or caprock, is composed of hard, erosion-resistant dolomite and limestone from the Lockport Formation. Directly beneath this strong layer lies the softer, more easily eroded shale of the Rochester Formation.
As the water plunges over the falls, it wears away the soft shale, undercutting the hard caprock until it collapses in large chunks. This process causes the falls to retreat upstream, slowly carving the 7-mile-long Niagara Gorge. The falls have retreated about 6.8 miles from their original position over thousands of years.
Water Diversion for Hydroelectric Power
The immense volume and drop of the Niagara River made it an obvious target for generating hydroelectric power. Both the United States and Canada divert a substantial portion of the river’s water upstream through massive tunnels and canals to power generating stations. This diversion began in the late 19th century and was formalized by international agreement in the mid-20th century.
The International Niagara Treaty of 1950 established rules to balance power generation with the preservation of the falls’ scenic beauty. The treaty dictates specific minimum flow requirements that must be maintained over the falls. During daylight hours in the tourist season (April 1 to October 31), the flow cannot be less than 100,000 cubic feet per second (2,832 cubic meters per second).
At night and during the non-tourist season, the minimum flow is halved to 50,000 cubic feet per second, allowing power companies to divert a larger amount of water. The International Niagara Control Works, a series of weirs and gates upstream of Horseshoe Falls, manages this precise daily and seasonal redirection.
Structural Engineering and Erosion Management
Beyond redirecting water for power, extensive engineering projects stabilize the rock structure and slow the natural rate of erosion. The inherent geological instability means the falls would otherwise continue to rapidly retreat and eventually collapse into a gentler cascade, losing their dramatic height.
One notable effort involved the 1969 dewatering of the American Falls, where a temporary cofferdam diverted the water to the larger Horseshoe Falls. This five-month-long project allowed the U.S. Army Corps of Engineers to study the rock face and the large accumulation of boulders, known as talus, at the base. While engineers decided against removing the talus, they reinforced the bedrock with steel bolts, cables, and concrete to prevent future rockfalls.
To enhance the scenic curtain of water, the crestline of the Horseshoe Falls has also been physically altered through excavation and filling. These “remedial works” were designed to spread the reduced water flow more evenly across the brink, creating the impression of a greater volume of water. These structural and flow-management efforts have successfully reduced the rate of erosion by more than 85 percent.