Plate Boundaries

The plate boundaries are the borders of tectonic plates, which are the huge moving slabs of the lithosphere. The lithosphere in turn consists of the crust and the upper mantle, being divided into plates that drift about over a sea of molten rock. There are three types: 1) convergent boundary, which is the point where the edges of two tectonic plates meet as they collide; 2) divergent boundary, which is when their borders separate from one another; 3) transform boundary, where the edges of two plates slide by, sideways without collision.

Convergent Boundary

It is the geological phenomenon when one plate collides against another. As it crashes against the other plate, it slips violently under its edge. The convergence of two slabs of the lithosphere releases a huge amount of energy, causing strong seismic and volcanic activities, with the formation and/or elevation of mountains. When an oceanic crust plate collides against a continental crust block, it sinks and slides under the continental plate. This is so, because the oceanic crust plate is much denser and heavier that the continental one. A good example of this is the convergence of the Nazca Plate, which form the floor of the South Pacific Ocean, and the South American Plate, with the former pushing and slipping under the latter. This collision gave birth to the Andes Mountain Range and it has caused the strongest earthquake in the world, affecting the Chilean coastal cities.

Divergent Boundary

It is the space marked when two tectonic plates drift away from one another. When this happens, new crust crops up in the form of molten magma from the depth of the upper mantle to fill in the gap. Thus, most divergent boundaries are located along mid-ocean ridges in the ocean floor where this separation takes place. In this case there is no seismic activity. The plates separation and the rising of new crust form a long ridge of rock; an example of this is the ridge in the Atlantic Ocean, where the South American Plate drifts away from the African Plate. When divergent boundaries take place on land, they form deep valleys, which are called rift valleys; an example of this is the Great Rift Valley in Eastern Africa, which marks the separation of the African Plate from the Arabian Plate.

Transform Boundary

It is formed when two plates slides past each other as they move in opposite direction, but they do not collide. In this type of boundary, there is no formation of new crust and the long line that mark the sliding is called fault. The San Andreas Fault in the State of California is a good example of this phenomenon and it is where the Pacific Plate slips sideways northwards by the North American Plate. Earthquake is also quite common along transform boundary.

Dow below, the Andes Mountain Range between Argentina and Chile. It was shaped by the convergent boundary between the Nazca Plate and the South American Plate.