【瀑布问答】尼亚加拉大漩涡是如何形成的？

How was the Whirlpool created?

The huge volume of water rushing from the Falls is crushed into the narrow Great Gorge, creating the Whirlpool Rapids that stretch for 1.6 kilometres (1 mi.). The water surface here drops 15 metres (50 ft.) and the rushing waters can reach speeds as high as nine mps (30 fps).

• The whirlpool is a basin 518 metres (1,700 ft.) long by 365 metres (1,200 ft.) wide, with depths up to 38 metres (125 ft.). This is the elbow, where the river makes a sharp right-angled turn.
• In the whirlpool, you can see the “reversal phenomenon.” When the Niagara River is at full flow, the waters travel over the rapids and enter the pool, then travel counter-clockwise around the pool past the natural outlet. Pressure builds up when the water tries to cut across itself to reach the outlet and this pressure forces the water under the incoming stream.
• The swirling waters create a vortex, or whirlpool. Then the waters continue their journey to Lake Ontario. If the water flow is low (water is diverted for hydroelectric purposes after 10 p.m. each night) the reversal does not take place; the water merely moves clockwise through the pool and passes to the outlet. Below the whirlpool is another set of rapids, which drops approximately 12 metres (40 ft.).