Why does desert oasis exist?

Related questions

1. Who owns pretty green brand?
2. Which is the largest oasis in the world?
3. When did Noel Gallagher join Oasis?
4. What is an example of an oasis?
5. What is Oasis What is its significance?
6. What is the biggest selling album ever?
7. What was Oasis first hit?
8. Who wrote Oasis songs?
9. What was Oasis first song?
10. When did Oasis last tour?

Tags

1. #becomes
2. #beneath
3. #rocks
4. #below
5. #underground
6. #desert
7. #oasis
8. #naturally
9. #source
10. #percolate
11. #river
12. #surface
13. #water
14. #there
15. #because
16. #plants
17. #accumulated
18. #which
19. #fertile