Niagara Falls is a product of erosion. The
force of the water tumbling
over the Horseshoe Falls continually causes large sections of rock to
erode and fall away.
The erosion is estimated at 1 foot (32 cm)
approximately every 10 years. The hard top layer of dolomite limestone
is underlain by softer layers of sandstone and shale. The thumbling
waters cut away the shale and sandstone layers until the undermined top
layer collapses, thus maintaining the vertical face of the Falls.
About 12,000 years ago, Niagara Falls was 7
miles (11 kilometers)
downstream from its present position. Until the early 1950's, the Falls
eroded at the average rate of 3 feet (approximately 1 metre) per year.
Since then major water diversions for the Sir Adam Beck #2 Generating
Station (1954) on the Canadian side of the border combined with the
construction of the International Control Works (1954-1963) to spread
the flow more evenly over the entire crestline of the Horseshoe Falls
and the construction of the Robert Moses Niagara Power Plant (1961) on
the American side of the Niagara River have sloved the rate of