Seafloor Spreading

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Across
  1. 2. _______ sounding is a type of sound used to determine the depth of water by transmitting (sending out) sound waves into water.
  2. 4. _________ boundaries form when tectonic plates move away from each other.
Down
  1. 1. An underwater mountain system created by tectonic plates it's the largest single volcanic feature on Earth
  2. 3. ________ boundaries gives us mountains, valleys, and trenches.