natural

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Across
  1. 2. Large ice formation)
  2. 4. Reef-building organism
  3. 5. Natural underground chamber
  4. 6. Erupting mountain
  5. 7. Large group of trees
  6. 9. Wetland with reeds
Down
  1. 1. Arid land with little vegetation
  2. 3. Lowland area between hills
  3. 5. Deep narrow valley
  4. 8. Shining celestial body