Waterfalls advance by retreating. Although the river runs downstream, falling water can excavate the rock beneath a waterfall, undermining its lip until collapse shifts the drop upstream. Height is the distraction. At Niagara, Victoria, Iguazu, Gullfoss, Kaieteur and Yosemite Falls, the spectacle invites attention upward, while the explanation often begins below, where water meets bedrock.The plun...More