Oceanic trench
Deep-sea trenches (german trenches ), called in geology deep-sea trenches, are mostly elongated but relatively narrow depressions of the sea floor. Make the lowermost portions of the earth's surface represents the deepest of all deep-sea trenches with a maximum of 11,034 m water depth, the Mariana trough in the Pacific.
Deep-sea trenches are formed in the earth's crust when tectonic plates collide as a result of plate tectonic processes and one slides under the other ( subduction ). On such a plate subduction zone dips at an angle of up to 90 ° from the bottom. The deep trough marks the spot where the two plates meet, for example, a continental and an oceanic plate. The lowest point of the trough are currently 3,000 to 4,000 m below the level of the surrounding ocean floor.
General
In most reference works (eg, encyclopedias and atlases ) and media, these deep-sea trenches that are located within or on the edge of ocean basins and between deep sleepers and backing as trenches or deep-sea trenches designated; this happens mostly in everyday language and the language of the geosciences. However, this is from the viewpoint of tectonics wrong because grabens caused by elongation, Subduktionsprozess is however characterized by convergence. Since a tectonic " ditch " but is always limited by deporting distortions and represents an overall extensional structure, have the elongated depressions at subduction zones (active continental margin ) correctly as troughs ( deep-sea trenches ), not " deep-sea trenches ," are referred to. In contrast to a deep sea deep-sea trenches are usually very elongated and can " submarine " contrary be considered to lie on the high mountain country than that.
Because of the movement of tectonic plates often leads to undersea volcanic eruptions and tsunamis that can cause devastating tidal waves and tsunamis.
History of the term
Only in the late 1940s and early 1950s began in oceanography to develop an idea of the morphology of those immense depths, which are among the most spectacular phenomena on the surface of the earth. More than half of the earth's surface is attributed to the deep sea, but withdrew because of hostile for humans extreme conditions long period of observation and research.
End of the 19th century began with the laying of the transatlantic cable, the interest in the bathymetry, the measurement of submarine landscapes tremendously. But even after the famous Challenger Expedition (1872-1876), who had explored the 8,164 m with measured up to that lowest point of the world's oceans in the Mariana trough on 23 February 1875 used to the (now obsolete ) term deep-sea trench not yet, but spoke generally of a deep sea (german deep ocean ).
Only in the 1920s the term was digging for geological structures. Be first used Johnstone in 1923 in his textbook on oceanography ( "An Introduction to Oceanography " ) the term trench ( trench engl. ) for the elongated but narrow channels at the base of the deep sea.
One of the lowest points of the earth, one in 1951 by the crew of the English survey ship Challenger II in the Mariana trough in a sea depth of 10,899 m by sonar ( 10,863 m per Drahtlotung ) determined place was called the " Challenger Deep ". Today, most deep-sea trenches have been measured by echo sounder, some have been visited by dive boats.
Overview deep-sea trenches
The six deepest deep-sea trenches of the earth, of which about 11 km deep, and the other depending on more than 10 km deep, are the Mariana Trench (up to 11,034 m), the Tonga Trench (up to 10,882 m), the Japan trench (up to 10,554 m ) the Kuril (up to 10,542 m), the Philippine Trench (up to 10,540 m) and the Kermadecgraben (up to 10,047 m); they are all located in the western Pacific.