system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does the coastline have beaches in some places and Rocky cliffs in other places, even right next to each other?
gpt
Different water currents. Normally cliffs would just keep eroding, and waves would wash the sand away. But in some places the currents *re-deposit* the sand up onto the shore, refreshing the beach so it doesn't disappear.