Question 6

(1)When two plates move towards each other, they would collide. This is called a convergent plate movement. As the plates collide, some crust is destroyed due to the impact, therefore this convergent boundary is also called a destructive boundary. When a continental plate and an oceanic plate collide, subduction occurs. The oceanic plate sinks under the continental plate as it is denser. The crust carrying the ocean melts underneath at the subduction zone due to the immense friction and high heat of the magma, which is acidic with higher silican and sulphuric content. The impact of the collision also causes cracks to form in the crust. The heat and pressure from the mantle forces the acidic magma to rise up these cracks. As the magma continues to rise up the cracks, it escapes onto the surface and solidifies, building up a volcano. Magma on the surface is now known as lava. Thus, an acid lava volcano is formed.(1) (2)divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. These areas can form in the middle of continents but eventually form ocean basins. Divergent boundaries within continents initially produce rifts which produce rift valleys. If the rifting process stops, a failed rift results. Therefore, most active divergent plate boundaries exist between oceanic plates and are often called oceanic rifts(2)(3) A transform fault is a fault which runs along the boundary of a tectonic plate. The relative motion of such plates is horizontal in either sinistral or dextral direction. Typically, some vertical motion may also exist, but the principal vectors in a transform fault are oriented horizontally. Not all faults are transform faults, and not all plate boundaries are transform faults.(3)
The features of the earths tectonic plates are (3)plates at our planet’s surface move because of the intense heat in the Earth’s core that causes molten rock in the mantle layer to move. It moves in a pattern called a convection cell that forms when warm material rises, cools, and eventually sink down. As the cooled material sinks down, it is warmed and rises again.

Scientists once thought that Earth’s plates just surfed on top of the mantle’s giant convection cells, but now scientists believe that plates help themselves move instead of just surfing along. Just like convection cells, plates have warmer, thinner parts that are more likely to rise, and colder, denser parts that are more likely to sink.

New parts of a plate rise because they are warm and the plate is thin. As hot magma rises to the surface at spreading ridges and forms new crust, the new crust pushes the rest of a plate out of its way. This is called ridge push.

Old parts of a plate are likely to sink down into the mantle at subduction zones because they are colder and thicker than the warm mantle material underneath them. This is called slab pull.(4)

(1) © Team 17701 TQ'98 (Cheong Kai Lin, Ng & Viren)
http://library.thinkquest.org/17701/high/tectonics/ptconv.html
(2)
http://en.wikipedia.org/wiki/Divergent_boundary

(3) http://en.wikipedia.org/wiki/Transform_boundary

(4) © The Regents of the University of Michigan. All Rights Reserved.
http://www.windows.ucar.edu/tour/link=/earth/interior/how_plates_move.html