Plate Tectonics Plate Movement Unit 3 Plate Tectonics Plate Movement

Lithospheric Plates Scientists believe that the lithosphere is broken into 10-12 major plates, plus many smaller ones. Plate boundaries are the area where two plates meet. Lithospheric plates can be either continental or oceanic.

Plate Movement Lithospheric plates are always moving at a rate of 2-20 cm per year. At plate boundaries plates can collide, separate, or slide past each other.

Convergent Plate Boundaries Convergent boundaries occur when the edges of plates move toward each other or collide. If the converging plates are equal in density the boundary will crumble upward and form mountains. If one of the plates is more dense than the other, the denser plate will slide below as they collide.

Subduction When one plate is pushed under another it is called subduction. When two oceanic plates collide and one sinks below, a deep-sea trench is formed. The sinking plate is heated causing it to partially melt, forming volcanoes in the plate above.

Divergent Plate Boundaries Divergent boundaries occur when the edges of plates move apart from each other or separate. As the plates separate rising magma cools and forms new seafloor. As the plates continue to spread a chain of volcanoes called a mid-ocean ridge will form.

Transform Plate Boundaries Transform boundaries occur when the edges of plates slide past each other. Lithosphere is neither created nor destroyed along a transform boundary. Destructive earthquakes are common along transform boundaries.