Ocean Floor Features

About this topic

The ocean floor has continental shelves (shallow edges of continents), steep continental slopes, the flat abyssal plains, mid-ocean ridges (where new crust forms), deep trenches (subduction zones, the Mariana Trench is nearly 11 km deep), seamounts and hydrothermal vents.

Sonar and satellite altimetry map the seafloor. Vents support unique ecosystems based on chemosynthesis rather than sunlight. Sea-floor spreading helped confirm plate tectonics.

The Mid-Atlantic Ridge is the longest mountain chain on Earth, about 16,000 km long and mostly under water, with a central valley where new crust is made. At the other extreme, the Challenger Deep in the Mariana Trench is about 10,935 m below the surface, so deep that Mount Everest would be covered by more than 2 km of water. Pressure there exceeds 1,000 atmospheres, like having an elephant standing on a thumbnail.

Hydrothermal vents, discovered in 1977, spew mineral-rich water heated to over 350 degrees C, and bacteria use hydrogen sulfide to make food, supporting tube worms, crabs and shrimp far from sunlight. Seamounts act as biodiversity hotspots. The continental shelf is where most fishing, oil and gas, and wind farms are found, while the abyssal plain is covered by slowly settling sediment called ooze, accumulating a few millimetres per thousand years. A common misconception is that the ocean floor is a flat sandy basin; it has mountains, canyons and volcanoes larger than on land. Another is that nothing lives in the dark; the deep sea has abundant specialised life.