Final answer:
The width of the western beach and dunes differ because of erosion and deposition processes.
Step-by-step explanation:
The reason for the difference in width between the western beach and dunes is that they are formed by different processes. The western beach is eroding faster than the dunes, which causes it to have a narrower width. On the other hand, the dunes are growing faster as wind-blown sand deposits on top of existing dunes, resulting in a wider width.