Final answer:
Wave action is the type of water erosion that causes the most changes along a coast, reshaping coastal landscapes through continuous energy impacting beaches and cliffs.
Step-by-step explanation:
The type of water erosion that causes the most changes along a coast is wave action. Ocean waves, with their continuous crashing against beaches and coastal cliffs, have a significant erosive impact. This erosive action can lead to the formation of various coastal features such as caves, arches, and eventually cliffs. Other types of water erosion like rill erosion, glacial melting, and gully erosion do not have the same profound effect on coastal landscapes as wave action does.
Gully erosion and rill erosion are more related to the effects of running water on land surfaces, such as in the case of the formation of the young gullies discovered by the Mars Global Surveyor. Glacial melting contributes to sea-level rise, which can alter coastlines over time, but the direct erosion by glaciers is more relevant to mountainous and polar regions rather than the immediate coastline. Ocean waves, powered by the wind, create and move along symmetrical ripple marks, indicating the back-and-forth motion typical of shallow marine environments. As a result of their energy, waves can reshape coastal landscapes dramatically and therefore are the primary cause of coastal changes due to erosion.