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Physical Features of the Bottom of the Ocean

The majority of planet Earth -- more than 70 percent -- is covered by water. Most of this water is contained within the planet's four interlinking oceans. Although most people are aware of the variety of geographical features on land, most also do not realize that beneath the deceptively calm waters, oceans have their own share of mountain ranges, volcanoes, plains and trenches.

Continental Shelf
- The continental shelf is the area of the ocean floor nearest to landmasses. The maximum depth of a continental shelf is about 650 feet. This area is normally the only part of the ocean floor most people ever get to see since the rest is largely inaccessible. This area is the most prolific region in the ocean because it permits the most light to reach the ocean floor. The predominant ground cover here is sand.
Continental Slope
- Beyond the continental shelf, the ocean floor begins to dip more steeply. This region is known as the continental slope. In some areas the continental slope is interrupted by submarine canyons and plateaus. The main covering on the floor of the continental slope is mud composed of sand and other sediment from the continental shelf. All ocean area beyond the continental slope is known as the abyss.
Mid-Oceanic Ridge
- The most bountiful geographic feature in the abyss is oceanic ridges. These underwater mountain ranges are present in all four of the oceans, and their combined length is about 50,000 miles. Formed when magma seeps through the tectonic plates, these ridges are characterized by higher temperatures.
Oceanic Trenches
- Also in the abyss, oceanic trenches are long, narrow trenches that result when two tectonic plates meet. Trenches form when one plate slips beneath another, and they are usually parallel to volcanic island arcs. These trenches are the deepest areas of the ocean. The deepest of all is the Challenger Deep of the Mariana Trench, which reaches 35,797 feet below sea level.
Volcanoes
- Submarine volcanoes can be part of a volcanic island arc or a hot-spot volcanic chain. Volcanic island arcs form where two tectonic plates collide. They always form an arc shape and are parallel to mountain ranges. Japan and the Philippines were formed as a result of volcanic island arcs. Hot-spot volcanic chains, on the other hand, are volcanoes that develop in a chain along the middle of a tectonic plate as the plate passes over a hot spot. The Hawaiian Islands are the result of a hot-spot volcanic chain.

Nature