Familiar landforms lie far beneath the ocean surface.
The oceans cover more than 70 percent of Earth's surface. Far beyond the reach of sunlight and shrouded in perpetual darkness, much of the ocean floor remains unseen by human eyes. Most people know more about the surface of the moon than the ocean floor. However, draining the water from the seas would reveal many familiar landforms, such as mountain ranges and sprawling plains.
Abyssal Plains
Most people think of plains as wide, flat expanses of sun-soaked land, often covered by fields of wheat, corn or grass. But another type of plains lie under the ocean, beyond the continental shelf: the vast abyssal plains. Found at depths ranging from 10,000 to 20,000 feet, abyssal plains are the flattest regions on Earth. Generally found between a continental rise and a mid-ocean ridge, the abyssal seafloor comprises more than 50 percent of Earth's surface. Abyssal plains consist of organic sediment -- sometimes thousands of feet thick -- layered over the volcanic rock of the oceanic crust.
Mid-Ocean Ridges
On land, converging tectonic plate boundaries create imposing mountain ranges like the Andes, Himalayas and Rockies. Under the sea, divergent plate boundaries create long mountain chains called mid-ocean ridges. The best-known mid-ocean ridge is the 6,200-mile Mid-Atlantic Ridge, which runs from the Arctic Ocean to a point just south of South Africa. Most of its peaks are submerged, but some are tall enough to rise above the ocean's surface, forming islands such as Iceland. The Mid-Atlantic Ridge is one part of a nearly 50,000-mile ridge system that extends through almost all of the oceans.
Volcanoes
Volcanism typically occurs along tectonic plate boundaries. Island chains such as the Hawaiian and Aleutian Islands are arcs of volcanoes that have grown from the ocean floor. The largest volcano in the world, Mauna Loa, rises about 13,000 feet above sea level. But measured from its base on the ocean floor, it's nearly 30,000 feet, which is taller than Mt. Everest. Lo'ihi, near the island of Hawaii, is an example of a submerged volcano, or seamount. Scientists expect Lo'ihi to break the surface of the Pacific Ocean in 40,000 years, and become the newest island in the Hawaiian chain.
Other Oceanic Landforms
Other oceanic landforms similar to those seen on the continents include undersea ridges, rift valleys and plateaus. The abyssal seafloor also has regions of rolling hills, and many submerged canyons traverse the continental shelves near river mouths.
Tags: plate boundaries, abyssal seafloor, boundaries create, Earth surface, Mid-Atlantic Ridge, mid-ocean ridge, more than
