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The lithosphere is broken up into several large pieces called crustal plates. These plates float on the denser semi-molten rock beneath them and move very slowly across the surface of the earth. Each plate move approximately 2cm per year interacting with each other in different directions.  The plates can move towards each other, away from each other as well as pass each other. The area where the edges of two plates meet is called a plate boundary or a plate margin.  There are three types of plate boundaries.  1. Where two plates are moving towards each other (converging), it is called a convergent plate boundary.  2. When two plates are moving away from each other (diverge), it is called a divergent plate boundary .  3. When two plates move past each other, it is called a transform plate boundary .

In some areas, plates are not moving towards or away from each other. Instead, at this plate boundary, they are sliding past each other. This plate boundary is also called a transcurrent plate boundary or a conservative plate boundary . At these plate boundaries, earthquakes occur because of the movement of the plates. These sometimes grind past each other during the movement. One famous transform plate boundary is at San Andreas Fault in California where several earthquakes occur each year. 

At divergent plate boundaries, plate move away from each other and creates a small space through which magma rises and cools on the surface creating or constructing new crust. For this reason, this plate boundary is also called constructive plate boundaries . The magma rising through weaknesses in the crust causes the formation of volcanoes and the plate movement causes earthquakes .  When divergent plate boundaries occur beneath the ocean, it creates a ridge . One famous example is the Mid-Atlantic Ridge which runs almost the entire length of the Atlantic Ocean. 

  Convergent plate boundaries  Convergent plate boundaries are also called destructive plate boundaries . At this boundary, plates collide causing earthquakes, volcanic activity and folding. As the plates push towards each other, it causes the rocks to crumble and fold. Some rocks fold downwards and some fold upwards forming very high mountains.  Where oceanic crust collide with continental crust, the denser oceanic crust is pushed under the less dense continental crust. This process is known as  subduction  and where it happens is known as a  subduction zone. As the oceanic crust is pushed below the continental crust, massive forces are generated. This causes the edge of the oceanic and continental plates to bend forming a V shaped depression called an ocean trench . The oceanic crust melts as it is pushed down into the mantle. This molten material may rise through weaknesses in the crust forming volcanoes near the plate boundary.  There are instance...

Earth Structure and Plate Tectonics For an introduction to the Earth's structure, click HERE! 👉lithosphere  The lithosphere is the rigid outer part of the earth consisting of the crust and the upper mantle. 👉asthenosphere The asthenosphere is the upper layer of the earths mantle, below the lithosphere 👉gutenburg discontinuity This is the distinct boundary between the core and the mantle 👉mohorovic discontinuity The boundary surface between the earth's crust and the mantle 👉crustal plates Crustal plates are large blocks or rigid layers of the earth's crust that are said to drift slowly. There are two types of plates. Oceanic and Continental.  👉 oceanic plate Oceanic plate or oceanic crust is also called SIMA as it is made up of basalt where silica (Si) and magnesium (Ma) are dominant. Oceanic crust is continuous around the earth surface and is 6-10km thick.  👉continental plate Continental plate or continental crust is also called SIAL as it consists of silica (Si) a...