What causes waterfalls to form?

Waterfalls form when a river flows over layers of rock with varying resistance to erosion. Softer rock erodes more quickly than harder rock, creating a vertical drop. Over time, the cascading water deepens the plunge pool at the base of the waterfall. Tectonic activity, glacial movement, or changes in sea level can also lead to the formation of waterfalls. Iconic examples like Niagara Falls illustrate the dynamic power of flowing water in shaping landscapes.