During highstands of sea level, the submarine canyons off the east coast of North America are many tens of kilometres from the coastline, and the downslope movement through them is slowed down dramatically or perhaps even ceases. Core samples taken in abyssal plains in the Atlantic Ocean off North Carolina show distinctive shelf molluscan fragments in gravity-flow deposits that have traveled hundreds of kilometres and that can be traced back through the Hatteras submarine canyon system. Sand and mud are carried down these systems, many times bypassing the slope-rise system to be carried directly out onto the abyssal plains of the ocean floor. During lowstands of sea level, rivers empty directly into the heads of many Atlantic canyons. Submarine canyons act as conduits to bring sand-sized sediments from the continental margins to the deep sea. Even so, many submarine canyons end in a series of distributary channels through the continental rise, and these channels often emerge in the deep sea on abyssal plains that are found adjacent to the continents, especially in the Atlantic basin. The submarine canyons have a substantial number of tributaries at their heads but generally do not have as many tributaries in their lower courses as do the land canyons. Moreover, the drainage pattern of submarine canyons differs from that of their terrestrial counterparts. The submarine canyons, for example, tend to have steeper side slopes, much higher gradients, and considerably narrower floors. In most cases, however, the characteristics of the submarine variety and those of the nearby land canyons are quite distinct. They usually are many kilometres in width for instance, the Grand Bahama Canyon measures 37 km (23 miles) at its widest point.Ī relatively large number of submarine canyons are located directly offshore of river canyons of adjacent land areas and may have once been connected to extensions of the latter. Most submarine canyons extend only about 48 km (30 miles) or less in length, but a few are more than 320 km (200 miles) long. The walls of the Grand Canyon of the Colorado River, by comparison, measure about 1.6 km (1 mile) high. Those of the Grand Bahama Canyon, which are thought to be the highest, rise nearly 5 km (3 miles) from the canyon floor. The majority of these V-shaped depressions have steep, rocky walls thousands of metres high. They also occur along the slopes of the Hawaiian Islands and possibly certain other ocean islands. Unlike deep-sea trenches, which are found in areas where one tectonic plate slides beneath another, undersea canyons are found along the slopes of most continental margins. Submarine canyons are so called because they resemble canyons made by rivers on land. They are rare on continental margins that have extremely steep continental slopes or escarpments. Submarine canyons originate either within continental slopes or on a continental shelf. Submarine canyon, any of a class of narrow steep-sided valleys that cut into continental slopes and continental rises of the oceans. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.
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