<P> The volume of water approaching the falls during peak flow season may sometimes be as much as 225,000 cubic feet (6,400 m) per second . The average annual flow rate is 85,000 cubic feet (2,400 m) per second . Since the flow is a direct function of the Lake Erie water elevation, it typically peaks in late spring or early summer . During the summer months, at least 100,000 cubic feet (2,800 m) per second of water traverses the falls, some 90% of which goes over the Horseshoe Falls, while the balance is diverted to hydroelectric facilities . This is accomplished by employing a weir--the International Control Dam--with movable gates upstream from the Horseshoe Falls . The falls' flow is further halved at night, and, during the low tourist season in the winter, remains a minimum of 50,000 cubic feet (1,400 m) per second . Water diversion is regulated by the 1950 Niagara Treaty and is administered by the International Niagara Board of Control (IJC). </P> <P> The verdant green colour of the water flowing over the Niagara Falls is a byproduct of the estimated 60 tonnes / minute of dissolved salts and "rock flour" (very finely ground rock) generated by the erosive force of the Niagara River itself . The current rate of erosion is approximately 1 foot (0.30 m) per year, down from a historical average of 3 feet (0.91 m) per year . It is estimated that 50,000 years from now, even at this reduced rate of erosion, the remaining 20 miles (32 km) to Lake Erie will have been undermined and the falls will cease to exist . </P> <P> The features that became Niagara Falls were created by the Wisconsin glaciation about 10,000 years ago . The same forces also created the North American Great Lakes and the Niagara River . All were dug by a continental ice sheet that drove through the area, deepening some river channels to form lakes, and damming others with debris . Scientists argue there is an old valley, St David's Buried Gorge, buried by glacial drift, at the approximate location of the present Welland Canal . </P> <P> When the ice melted, the upper Great Lakes emptied into the Niagara River, which followed the rearranged topography across the Niagara Escarpment . In time, the river cut a gorge through the north - facing cliff, or cuesta . Because of the interactions of three major rock formations, the rocky bed did not erode evenly . The top rock formation was composed of erosion - resistant limestone and Lockport dolostone . That hard layer of stone eroded more slowly than the underlying materials . The aerial photo on the right clearly shows the hard caprock, the Lockport Formation (Middle Silurian), which underlies the rapids above the falls, and approximately the upper third of the high gorge wall . </P>

Where does the water of niagara falls come from
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