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USGS Geology in the Parks

The action is at the edges!

If you are lucky enough, or sometimes, unfortunate enough to live where two plates meet, you've probably had first-hand experience with moving plates! That's because many potentially catastrophic geologic phenomena, such as earthquakes, volcanic eruptions, and tsunamis originate at the narrow boundary zones between plates.

There are three basic things that can happen where the edge of one plate meets another. The plates can push against each other, producing a convergent plate boundary, the plates can move apart, forming a divergent plate boundary, or the plates can slip past each other side to side, which geologists call transform plate boundaries. Wherever plates grind against each other, you can expect earthquakes.

Divergent plate boundary

Divergent plate boundaries

Almost all the Earth's new crust forms at divergent boundaries, but most are not well known because they lie deep beneath the oceans. These are zones where two plates move away from each other, allowing magma from the mantle to rise up and solidify as new crust. Click here to learn more about divergent plate boundaries.


Convergent plate boundary

Convergent plate boundaries

This image shows a slice through the Earth at a convergent plate boundary. This view illustrates just one of the ways that plates behave when they collide. In this case, one plate is pulled beneath another (subduction), forming a deep trench. The long, narrow zone where the two plates meet is called a subduction zone.

The fate of the colliding plates depends mostly on what type of lithosphere they are made of. Plates with thick, buoyant continental lithosphere behave very differently from plates with thin, dense oceanic lithosphere! Click here to learn more about convergent plate boundaries.

Transform plate boundary

Transform plate boundaries

At transform plate boundaries plates grind past each other side by side. This type of boundary separates the North American plate from the Pacific plate along the San Andreas fault, a famous transform plate boundary that's responsible for many of California's earthquakes.

| Into Earth | | Putting the pieces toge ther | | Action at the edges |
| National Parks by Tectonic Regions |
| Earth through time | | Detailed version: This Dynamic Earth |


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