# 2.5: Types of Plate Boundaries

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Categorization of plate boundaries is based off of how two plates move relative to each other. There are essentially three types of plate boundaries, which are divergent, convergent, and transform. In the case of divergent plate boundaries, two of earth’s plates move away from each other. Spreading centers and areas where new ocean floor are generally located at divergent plate boundaries. An example of a divergent plate boundary is the Mid-Atlantic Ridge. Depending on what type of lithospheric crust each diverging plate is, whether oceanic or continental, varying geographic features are formed. For example, when two continental plates diverge from each other, an ocean basin is created due to the separation of land. On the other hand, if two oceanic plates diverged, a mid ocean ridge would form, which is also known as a spreading center. Divergent plate boundaries are commonly associated with shallow earthquakes.

When two plates move towards each other, the boundary is known as a convergent boundary. As previously mentioned, depending on what type of crust each converging plate is, different geographic features are formed. When two continental crusted plates converge, they eventually collide and end up producing mountains; this was how the Himalayan Mountains were created. Neither continental crust will subduct underneath one another because of their similar densities. When two oceanic plates converge, the denser plate will end up sinking below the less dense plate, leading to the formation of an oceanic subduction zone. When an oceanic plate converges with a continental plate, the oceanic crust will always subduct under the continental crust; this is because oceanic crust is naturally denser. Convergent boundaries are commonly associated with larger earthquakes and higher volcanic activity. Whenever a subduction zone is formed, the subducted plate will end up being partially melted by the earth’s internal magma and molten. This melting leads to heat being transferred upwards and uplifting the crust, eventually developing into a volcano. Subduction zones are the reason why oceanic crust older than 200 million years old cannot be found. Old, dense crust tends to be subducted back into the earth. An example of a subduction zone formed from a convergent boundary is the Chile-Peru trench.

The last type of plate boundary is the transform boundary, which is where two plates slide past one another. Unlike the other two types of plate boundaries in which new seafloor is created at divergent boundaries and where old seafloor is subducted at convergent boundaries, transform plate boundaries neither create nor destroy the seafloor. The rubbing caused by the sliding is what causes earthquakes along the transform faults; one example would be the San Andreas fault.