Convergent Boundary |
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Here crust is destroyed and recycled back into the interior of the Earth as one plate dives one another. These are known as Subduction Zones - mountains and volcanoes are often found where plates converge. I chose this video because it shows and describes (in subtitles) what happens during and after a Convergent Boundary. There are 3 types of convergent boundaries: Oceanic-Continental Convergence; Oceanic-Oceanic Convergence; and Continental Convergence.
When an oceanic plate pushes into and subducts under under a continental plate, the overriding continental plate is lifted up and a mountain range is created. Even though the oceanic plate as a whole sinks smoothly and continuously into the subduction trench, the deepest part of the subducting plate breaks into smaller pieces. These smaller pieces become locked in place for long periods of time before moving suddenly and generating large earthquakes. Such earthquakes are often accompanied by uplift of the land by as much as a few meters.
When two oceanic plates converge one is usually subducted under the other and in the process a deep oceanic trench is formed. The Marianas Trench, for example, is a deep trench created as a result of the Philippine Plate subducting under the Pacific Plate. Oceanic-Oceanic plate convergence also results in the formation of undersea volcanoes.
When two continents meet head-on, neither is subducted because the continental rocks are relatively light and, like two colliding icebergs, resist downward motion. Instead, the crust tends to buckle and be pushed upward or sideways. The collision of India into Asia 50 million years ago caused the Eurasian Plate to crumple up and override the Indian Plate. After the collision, the slow continuous convergence of the two plates over millions of years pushed up the Himalayas and the Tibetan Plateau to their present heights.
At divergent boundaries new crust is created as one or more plates pull away from each other. Oceans are born and grow wider where plates diverge or pull apart. When a diverging boundary occurs on land a 'rift', or separation will arise and over that time that mass of land will break apart into distinct land masses and the surrounding water will fill the space between them.
Transform-Fault Boundaries are where two plates are where two plates are sliding horizontally past one another. These are also known as transform boundaries or more commonly as faults. Most transform faults are found on the ocean floor. They commonly offset active spreading ridges, producing zig-zag plate margins, and are generally defined by shallow earthquakes. A few, however, occur on land.
Mountains
Himalayas- The Himalayan mountain range and Tibetan plateau have formed as a result of the collision between the Indian Plate and Eurasian Plate which began 50 million years ago and continues today.
Andes- The leading edge of the Nazca Plate is subducting below the South American Plate at a plate boundary known as a subduction zone. During this subduction some Nazca crust is scraped off along base of the Andes, adding height to the entire range.
Aleutians- The Aleutian Islands were formed by interactions between the North American and Pacific plates. They are located on the southern edge of the North American plate where it collides with the Pacific to form a convergent plate boundary. In this area, the location of the plate boundary is marked on the ocean floor by the Aleutian Trench.
Hawaii- The Hawaiian Islands where formed by a hot spot occurring in the middle of the Pacific Plate. While the hot spot itself is fixed, the plate is moving. So, as the plate moved over the hot spot, the string of islands that make up the Hawaiian Island chain were formed.
The Mariana Trench- The Mariana Trench was created by the process that occurs in a subduction zone, where two massive slabs of oceanic crust collide. At a subduction zone, one piece of oceanic crust is pushed and pulled underneath the other, sinking into the Earth's mantle, the layer under the crust. Where the two pieces of crust intersect, a deep trench forms above the bend in the sinking crust. In this case, the Pacific Ocean crust is bending below the Philippines crust.
Mid-Atlantic Ridge- a mid-ocean ridge, a divergent tectonic plate boundary located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. It separates the Eurasian Plate and North American Plate in the North Atlantic, and the African Plate from the South American Plate in the South Atlantic.