Niagara Falls

Niagara Falls is a group of three large waterfalls on the Niagara River, on the border between Canada and the United States. On 29 March 1848 the falls stopped. Strong winds had pushed ice from Lake Erie into the mouth of the river, jamming it, and for about thirty hours the water slowed to a trickle.^[1] Local people walked out on the exposed riverbed, picking up objects that had been under the falls. It is the only time a waterfall has been visited from the inside.

Switched off

In 1969, engineers deliberately turned off the American Falls, the smaller of the main falls, for several months. They built a temporary dam of rock and earth upstream to divert the water over the larger Horseshoe Falls, so that they could study the loose rock at the foot of the American Falls and whether it needed to be removed.^[2] In the end they decided to leave it, and turned the falls back on.

It is the only river feature to have been switched off for maintenance and found to be working normally.

Moving

The falls are slowly moving upstream as the water wears away the rock at the edge. Over thousands of years they have retreated about eleven kilometres from where they began. Water is now diverted for hydroelectric power, which slows the erosion to around 30 centimetres a year or less. At the old rate, the falls would eventually reach Lake Erie, in about 50,000 years, and become a much less interesting lake.

• 1848: stopped by ice (about 30 hours).
• 1969: American Falls turned off (months).
• Moving upstream: slowly.
• Arriving at Lake Erie: not soon.

See also

• River – which it is part of
• Lake – where it may one day end up
• Ice – which once stopped it

References

1. Torrent, T. (1848/2003). It Stopped. Fictional reprint.
2. Cofferdam, C. (1969/2010). “Off for Maintenance”. Engineering Notes 1: 1.
3. Erosion, E. (1999). Fifty Thousand Years. Gorge Press.