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Plate Boundaries

The earth’s lithosphere is made of the crust and upper mantle. But this is not one big piece! Instead, it is broken into several pieces called tectonic plates. These plates meet at plate boundaries!
A diagram of tectonic plates and subduction zones.

Types of Plate Boundaries

The Earth’s plates are always moving, but their movement is very slow. In one year, most plates move less than the length of one of your fingers! Even though we can’t see their movement, scientists have evidence that the plates move.
World map of tectonic plates.

There are three different kinds of movement at plate boundaries!

The plates can move next to each other, towards each other, or away from each other. Each of these kinds of movement creates a different type of plate boundary. The picture above and video below shows what these different types of movement look like.

Divergent Boundaries

Plates move away from each other at divergent boundaries. Magma comes up from the Earth’s mantle between the two plates. When it reaches the crust, it cools and forms new igneous rock. This new rock becomes part of the crust of the two plates.
Most divergent boundaries are found in the ocean. The new crust that forms at the boundary is sima, or oceanic crust. It often rises higher than the rest ocean floor, forming an underwater mountain range. This is calledmid-ocean ridge. The plates then continue to move the new seafloor away from the boundary.

Convergent Boundaries

Plates move towards each other at convergent boundaries. When an oceanic plate meets a continental or another oceanic plate, subduction occurs. This means that the heavier oceanic plate slides underneath the other plate. The oceanic crust melts when it meets the mantle, forming magma. Volcanoes and oceanic trenches often form at convergent boundaries.
A diagram of plate subduction.

Subduction creates deep trenches and volcanoes!

When two continental crusts meet, there is no subduction. The continents’ crust is too light to get pushed down into the earth. Instead, the crust gets pushed up, forming mountain ranges.
Diagram of tectonic plates forming a mountain.

Mountain ranges form when continental plates collide!

Transform Boundaries

At transform boundaries, plates slide past each other. Unlike the other boundaries, the crust isn’t created or destroyed. Instead, the crusts move in opposite directions next to each other. Movement at transform plate boundaries is rarely smooth. As plates move past each other they get stuck on each other. This causes energy to build up. The release of that energy causes an earthquake. The San Andreas Fault is a transform boundary that has caused many earthquakes.

Other Great Resources

Tectonic Plates and Plate Boundaries – GNS Science: 
Understanding Plate Motion – USGS: https://pubs.usgs.gov/gip/dynamic/understanding.html
What is Plate Tectonics? – Live Science: https://www.livescience.com/37706-what-is-plate-tectonics.html
BrainPOP Video on Plate Tectonics: 

Written by: Alexa Wnorowski.