Constructive margins occur when two plates move away from each, and in the gap between the two plates new crust is created. This process can happen in two ways, as it can occur when two oceanic plates move away from each other or when two continental plates move away from each other. When two oceanic plates move away from each other the term given to it is sea floor spreading. The gaps created between the two plates are then filled with magma, which creates new basalt rock to fill the gap. An example of this is the mid Atlantic ridge where the Eurasian and African plates are moving away form the North and South American plates. Here is a diagram showing the movement of these plates and the land formations they create.
Where the two plates have moved apart the magma which takes its place forms a mountainous landscape under the sea with mountains larger than Everest. These mountains can be so big that they can form new land about sea level; Iceland is created in this way and is getting larger all the time from plate movement. The other possibility is that two continental plates could be moving apart. When this happens it creates a rift valley, like in Africa. Section of the crust fall down when the plates move apart creating block valleys over 600m deep in places. In some places the blocks can slip so much that the space gets invaded with water, like the red sea.
The second type of plate boundary is deconstructive. This is when continental plate meets oceanic plate. This causes the oceanic to be subducted which then melts due to the friction forming magma and causes additional pressure, as the new magma is more viscous rises trying to find a way to the surface, which usually forms a volcano. The subduction can also cause large earthquakes due to the extra pressure.
Two continental plates can also move towards each other so that they make huge mountain rangers. The Himalayas were formed in the manner as India crashed in to the Indo-Australian plate. As continental crust does not sink both continental crusts are forced to move upwards, this is when fold mountains occur and where the crust is at its thickest. Where oceanic plates collide Island arches and volcanoes are formed. This is happening in the area surrounding Japan, where the Eurasian plate is meeting the pacific.
The final type of plate margin is the conservative margin. This is where two plates rub against each other. This occurs along the San Andreas Fault by Los Angeles. The diagram shows the motion and factor evolved with this kid of plate movement.
The way the world is constructed is due to the movements of the plates, which make up its crust. The way the earth looks now will be different in the future as the plates are constantly moving, and it was this movement that changed the worlds appearance from the single continent Pangea to the way things are today. The landforms that occur at the plate boundaries all contribute and sculpt the way our surface is.