Figure 16.18

Niagara Falls knickpoint. (A) A waterfall migrates upstream when the more resistant lip of rock that forms it is undercut and collapses into the plunge pool. (B) Niagara Falls, on the United States–Canada border, is one of the best-known waterfalls in the world. Niagara Falls consists of three waterfalls. The largest is Horseshoe Falls in Canada; American Falls and Bridal Veil Falls are in the United States. The Niagara knickpoint has retreated upstream (south) by almost 11 km (7 mi) during the last 10,000 years.