fall

A waterfall is a place where water drops vertically or nearly so due to an abrupt steepening of a river channel. Waterfalls are characterized by their erosive power, which can cause them to migrate upstream over time. This erosion often creates plunge pools beneath the falling water.1

Waterfalls can form in several ways:
* Differential Erosion: This occurs when rocks of varying resistance are present. Harder rocks overlie weaker ones, and the weaker rock erodes faster, leaving the harder rock as a ledge over which water falls. A prime example is Niagara Falls.2
* Constructional Processes: These include the precipitation of calcium carbonate, lava flows damming rivers, ice dams, and debris from landslides or avalanches.3
* Discordance of River Profiles: This can result from faulting, glaciation (creating features like hanging valleys), or karst topography.1

A "rockfall" is a mass of falling or fallen rocks. A "rockslide" is a rapid downward movement of rock fragments sliding over an inclined surface. Landslides are classified by their movement type, which can include falls, slides, or flows.456