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Deep ocean trenches

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Deep ocean trenches

  1. 1. By Connor
  2. 2.  Deep-sea trenches generally lie seaward and parallel to arcs or mountain ranges of the continental margins.  They are closely associated with and found in subduction zones— that is, locations where a lithospheric plate bearing oceanic crust slides down into the upper mantle under the force of gravity.
  3. 3.  Both types of subduction zones are associated with large earthquakes that originate at a depth of as much as 700 km (435 miles).  The deep earthquakes below subduction zones occur in a plane that dips 30° or more under the overriding plate.  Typical trench depths are 8 to 10 km (5 to 6 miles). The longest trench is the Peru-Chile Trench, which extends some 5,900 km (about 3,700 miles) along the west coast of South America.
  4. 4.  Ocean trenches are the deepest parts of the ocean. They are also called submarine valleys.  An ocean trench is a long, deep depression in the ocean floor, similar to deep chasms on the Earth’s dry land.  Some trenches are near continental shelves. Others are found near chains of volcanic islands, often called volcanic arcs.  Some volcanic arcs include the Aleutians, and the island nations of Japan and the Philippines
  5. 5.  Trenches are formed as a result of plate tectonics, or the movement of the Earth’s crust.  Tectonic plates slip underneath each other in a process known as subduction.  When the leading edge of a heavy plate meets the edge of a lighter plate, the heavier plate bends downward.  This place where the heavier plate melts (subducts) beneath the lighter one is called the subduction zone.
  6. 6.  Ocean trenches can be formed by subduction between continental crust and oceanic crust. Continental crust is always lighter.  The long series of Peru-Chile Trenches off the west coast of South America is formed by the oceanic crust of the Nazca plate subducting beneath the continental crust of the South American plate.  Ocean trenches can also be formed when two plates carrying oceanic crust meet. These are more rare.
  7. 7.  The Mariana Trench, in the South Pacific Ocean, is formed as the massive Pacific plate subducts beneath the Philippine plate.  The deepest place on Earth is called the Challenger Deep. It is found in the Mariana Trench in the Pacific Ocean, near the island of Guam.  The Challenger Deep is 10,994 meters (36,070 feet) below the ocean’s surface.  For comparison, Mount Everest, the world’s tallest mountain, is 8,850 meters (29,035 feet) above sea level. Mount Everest could fit inside the Mariana Trench with more than 2 kilometers (1 mile) to spare
  8. 8.  In June 2009, scientists sent an unmanned deep-sea robot, the Nereus, to explore the Mariana Trench and Challenger Deep.  The vehicle had to be designed to withstand extreme pressure of 15,000 pounds per square inch— more than 1,000 times the pressure felt at sea level.  Scientists want to learn more about the subduction process that created the trench.
  9. 9.  The deepest part of the Atlantic Ocean is the Puerto Rico Trench.  It is just over 8,600 meters (28,232 feet) deep and is about 280 kilometers (175 miles) long.  The Puerto Rico Trench was formed by the North Atlantic plate sliding beneath the Caribbean plate.
  10. 10.  Animals that live in ocean trenches have to survive a habitat of extreme pressure.  Most organisms collected from the Challenger Deep have been microscopic. The organisms, or foraminifera, are similar to algae or slime-molds.  Scientists believe the foraminifera they found at the bottom of the Challenger Deep are similar to Earth’s earliest life forms.
  11. 11. National geographic