This is kind of old news, but it has a nice perspective of what might be found if the water stops flowing at Niagara Falls.
From LiveScience.com:
or the first time in nearly 50 years, officials are debating turning off the tap for part of Niagara Falls.
Officials have proposed drying out two of the three waterfalls that make up Niagara Falls — American Falls and Bridal Veil Falls — so that workers can repair the aging pedestrian bridges that span the rapids along the river that feeds the falls. (Horseshoe Falls is the third waterfall that makes up Niagara.) The proposed “dewatering” would do more than provide the curious with a rare chance to see the landscape transformed. It could also yield unprecedented insights into the rock-cutting process that is hidden beneath the flow of millions of gallons of water.
Niagara Falls are “very spectacular aesthetically, but they’re not studied a lot geologically,” said Marcus Bursik, a geologist with the University at Buffalo, who is proposing to measure some of the changes in the falls if the water is cut off. The new plan could provide a one-time chance to do some of that geological research, he added.