system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 - How can oases exist in deserts? Where does the water come from? How come they don't just vaporize? And where do trees and plants there grow from?
gpt
Oases exist where groundwater comes to or near to the surface. This usually happens in low places, where all the underground water flows end up. The water itself comes ultimately from rains, which, however rare, occur in every desert. The water then seeps down through the ground until it reaches a barrier made of impermeable rock, and then flows down along that barrier towards an oasis, where it accumulates. This way the infrequent rainfall over many thousands of square kilometers of desert can support a single small oasis in the low place of the area.