The correct answer is - seamounts.
The seamounts are isolated mountain ranges on the ocean floor, totally being under water. A seamount is geological formation that is the result of a volcanic activity. When there was volcanic activity the magma was constantly rising up and pilling new layers of new rocks as it was cooling off. Over time it managed to create underwater mountains, known as seamounts, on the places where the volcanic activity was present. The seamounts can be pretty high and they rise from the seafloor anywhere from 1,000 meters to 4,000 meters.