What causes waterfalls to erode over time?

Waterfalls erode over time as the flowing water wears away the rock at their base. The force of the water creates a plunge pool, gradually undercutting the harder rock above. Sediments carried by the water further enhance the erosion process. Eventually, this causes the waterfall to recede upstream, altering its shape and position over time. Famous waterfalls, like Niagara Falls, showcase this continuous geological transformation.