The Niagara River, as is the complete Great Lakes Basin of which the river is an essential part, is a bequest of the last Ice Age. 18,000 years ago southern Ontario was sheltered by ice sheets 2-3 kilometers broad. As they sophisticated southward the ice sheets gouged out the basins of the Great Lakes. Then as they melted northward for the last time they free enormous quantities of melt water into these basins. Our water is "fossil water"; less than one percent of it is renewable on a yearly foundation, the respite leftover from the ice sheets.
The Niagara Peninsula became gratis of the ice about 12,500 years ago. As the ice retreated northward, its melt waters began to flow down during what become Lake Erie, the Niagara River and Lake Ontario, down to the St. Lawrence River, and, in conclusion, down to the sea. There were initially 5 spillways from Lake Erie to Lake Ontario. Eventually these were abridged to one, the original Niagara Falls, at Queenston-Lewiston. From here the fall began its steady corrosion during the bedrock.
However, about 10,500 years ago, through interplay of environmental effects as well as alternating retreats and re-advances of the ice, and rebounding of the land when at large from the intense weight of the ice (isostatic rebound), this process was intervallic. The glacial melt waters were rerouted during northern Ontario, bypassing the southern route. For the next 5,000 years Lake Erie remain only half the size of nowadays, the Niagara River was condensed to regarding 10% of its present flow, and a much-reduced Falls delayed in the area of the Niagara Glen.
It was a brief and aggressive stumble upon, geological instant lasting only weeks, maybe even only days. In this instant the fall of the youthful Niagara River intersected an old riverbed, one that had been covered and preserved during the last Ice Age. The fall turned into this hidden gorge, tore out the hostile remains that filled it, and battered the old river base clean. It was perhaps not a falls at all now but a huge, churning rapid. When it was all over it left after a 90-degree turn in the river we know nowadays as the Whirlpool, and North America's major sequence of standing impression we know today as the Whirlpool Rapids.