Here's why:

* Erosion: The process of wearing away and transporting rock and soil by forces like waves, wind, and water.

* Deposition: The process of dropping or settling of eroded material in a new location.

Sea arches are formed when waves repeatedly crash against a headland, eroding the rock. Over time, this erosion creates a cave. If the cave erodes through the headland completely, it forms an arch.

Let me know if you have more questions!