Geography of the Ocean floor

(14.1 & 14.2)

Geography of the Oceans

The world ocean can be divided into four main ocean basins the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, and the Arctic. The Pacific Ocean is the largest ocean. It covers more than half of the ocean surface area on Earth. It is also the world's deepest ocean, with an average depth of 3940 meters. The Atlantic Ocean is about half the six of the Pacific Ocean. The Atlantic and Pacific Oceans ate bounded to the east and west by continents. The Indian Ocean is slightly smaller than the Atlantic Ocean. The Indian Ocean is located almost entirely in the southern hemisphere. The Arctic Ocean is only a little more than one-quarter as deep as the rest of the oceans.

Continental Margins

The zone of transition between a continent and the adjacent ocean basin floor is known as the continental margin. In the Atlantic Ocean, thick layers of undisturbed sediment cover the continental margin. This region has very little volcanic or earthquake activity. In the Pacific Ocean, oceanic is plunging beneath continental crust. This force results in a narrow continental margin that experiences both volcanic activity and earthquakes. The continental shelf is the gently sloping submerged surface extending from the shoreline. The shelf is almost nonexistent along some coastlines. Continental shelves contain important mineral deposits, large reservoirs of oil and natural gas, and huge sand and gravel deposits. Marking the seaward edge of the continental shelf is the continental slope. This slope is steeper than the shelf and it marks the boundary between continental crust and oceanic crust. Steep-sided valleys known as submarine canyons are cut into the continental slope. These canyons may extend to the ocean basin floor. Turbidity currents are occasional movements of dense, sediment-rich water down the continental slope. They are created when sand and mud on the continental shelf and slope are disturbed perhaps by and earthquake and become suspended in the water. In regions where trenches do not exist, the steep continental slope merges into a more gradual incline know as the continental rise.

Ocean Basin Floor

Between the continental margin and mid-ocean ridge lies the ocean basin floor. This region includes deep-ocean trenches, very flat areas known as abyssal plains, and tall volcanic peaks called sea mounts and guyots. Deep-ocean trenches ate long, narrow creases in the ocean floor that form the deepest parts of the ocean. A portion of the one trench the Challenge Deep in the Mariana Trench. Trenches form at sites of plate convergence were one moving plate descends beneath another and plunges back into the mantle. Earthquakes and volcanic activity are associated with these regions. Abyssal plains ate deep, extremely flat features. In fact, these regions ate possibly the most level places on Earth. The sediments that make up abyssal plains ate carried there by turbidity currents or deposited as a result of suspended sediments settling. The submerged volcanic peaks that dot the ocean floor are called seamounts. They are volcanoes that have not reached the ocean surface. Some seamounts form at volcanic hot spots. This chain stretches from the Hawaiian islands to the Aleutian trench. Once underwater volcanoes reach the surface, they form islands. Over time, running water and wave action erode there volcanic islands to near sea level.

Mid-Ocean Ridges

The mid-ocean ridge is found near the center of most ocean basins. It is an interconnected system of underwater mountains that have developed on newly formed ocean crust. This system is the longest topographic feature on Earth's surface. These are offset by large transform faults where plates slide past each other horizontally, resulting in shallow earthquakes. A high amount of volcanic activity takes places along the crest of the mid-ocean ridge. Seafloor spreading occurs at divergent plate boundaries where two lithosphere plates ate moving apart. New ocean floor is formed at mid-ocean ridges as magma rises between the diverging plates and cools. Hydrothermal vents form along mid-ocean ridges. These are zones where mineral-rich water, heated by the hot, newly-formed oceanic crust, escapes through cracks in oceanic crust into the water. As the super heated, mineral rich water comes in contact with the surrounding cold water, minerals containing metals such as sulfur, iron, copper, and zinc precipitate out and are deposited.