Niagara Falls (Waterfalls)

Niagara Falls

Niagara Falls, a spectacular waterfall in the NIAGARA RIVER, is the world's greatest waterfall by volume at 2832 m3. It is split in two by Goat Island. The American Falls are 59 m high (21-34 m to rock debris at the base of the falls) and 260 m wide and carry about 10% of the flow. The Canadian, or Horseshoe, Falls are 54 m high and 670 m wide, with the remaining 90% of the flow. However, only the Canadian Falls fall freely to the Maid-of-the-Mist pool, where they have excavated a pool as deep or deeper than they are tall. The falls were formed some 14 000 years ago as retreating glaciers exposed the NIAGARA ESCARPMENT, permitting the waters of Lake ERIE, which formerly drained south, to flow northward into Lake ONTARIO.

The falls have eroded the soft shales and limestones of the escarpment at an average rate of 1.2 m per year and now stand 11 km from their place of origin at present-day QUEENSTON. Their recession rate has been variable though, as the volume of water flowing from the upper Great Lakes controls it. Because of changing land and lake levels in northern Ontario, the flow through the Niagara River was reduced to 10% of its present volume for a period of 5000 years. During this time the falls were almost stationary.