Incredible nature

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Across
  1. 2. Elevated portion of earth
  2. 3. A natural flowing water course
  3. 5. A rupture of the planetary surface that allows hot lava to escape
  4. 7. Large water body surrounded by land
Down
  1. 1. A point in a river where the water flows in a vertical drop
  2. 4. A piece of land surrounded by water
  3. 6. A natural underground hollow space