After seeing the sheer size of Niagara Falls, it is almost impossible to think that such a volume of water could ever stop, but it has – twice, in fact, and one of those was entirely down to humans.
The first was a simple tale of unfortunate timing. On March 29, 1848, local people woke to find the enormous waterfall no longer had any water flowing over it. The river had entirely stopped, causing the entire area to dry out, creating an otherworldly sight. It happened because huge blocks of ice in Lake Erie suddenly got caught in strong winds that pushed them toward the source of the Niagara River. Somehow, the entire channel got blocked, creating a natural dam that prevented all water from passing through. This blockage remained in place for around 30 hours before the winds shifted, releasing the ice as the weight of the water caused it to fail.
The only other time that Niagara Falls has stopped, though, is a fascinating effort from the U.S. Army Corps of Engineers.
Niagara Falls is made of three falls, the second largest of which is American Falls. It is easily spotted by the huge build-up of rock at the base of the falls, called a talus, that has slowly accumulated over the years due to rockslides. This became a concern for the US, as they worried that continued deposits of rock would shorten the water drop and perhaps stop the falls entirely.
So, the US and Canada came to an agreement – they would stop the flow of water over American Falls for five months. During this time, they would study how the waterfall deposited rock, its geological composition, and whether they would need to intervene and remove some debris.
The mission was a gargantuan effort. Over 1,200 trucks delivered around 28,000 tonnes of rock into the river upstream of American Falls over the course of three days in 1969. The water was diverted towards Horseshoe Falls and the water supply to American Falls dwindled to just a trickle, drying out the massive cliff of rocky debris.
The dry waterfall revealed millions of coins that had been thrown into the river over the years, causing a mad rush of residents and tourists. Two bodies were pulled out, which sounds macabre but was actually a surprisingly low amount for such a large river – particularly one infamous for suicides and daredevil stunts.
Probing into the rock, the engineers looked for fault lines and points of stress, trying to understand whether any more areas were ready to give way. They reinforced areas of weakness with bolts and drilled holes to allow water an alternative path, reducing points of overwhelming pressure. In doing so, the team could identify how likely it was that further rockfall would occur and over what timeframe.
After the study period, the engineers decided against removing any rock – it would be a mammoth task and cost a huge amount of money which isn’t usually reserved for making waterfalls prettier. The dam was removed and water flowed across the falls once more, marking the last time it was dry. All that remains is a few images of the rocky falls, which look rather strange without thousands of gallons of water flowing over them.
Source Link: America Once Made Niagara Falls Stop Flowing For Science
