11.   These are rocket-shaped projectiles loaded with vitrified waste, and dumped from ships to plunge into soft sediments on the ocean floor.

12.   These of course raise little or no dust unless the impactor reaches the ocean floor before detonating.

13.   They continued to pursue their own explanations for the mysterious mountains on the ocean floor.

14.   This took the form of an unusual series of stripes, discovered as ships towing magnetometers trolled above the ocean floor.

15.   While nodules are loose deposits, lying on the sea bed, sulphides are massive deposits below the ocean floor.

16.   Ships towing huge magnets trolled the ocean floor.

17.   A chasm in the ocean floor.

18.   Their company has discovered new oil deposits below the ocean floor.

19.   They were trolling the ocean floor.

20.   The island was created by an upheaval of the ocean floor.