Types of Plate Boundaries

volcanic landscape with glaciers and caldera lake
Active subduction along the southern Alaska coast has formed a volcanic arc with features including the Katmai caldera and neighboring Mount Griggs. Katmai National Park and Preserve, Alaska.

NPS photo.

Introduction

The landscapes of our national parks, as well as geologic hazards such as earthquakes and volcanic eruptions, are due to the movement of the large plates of Earth’s outer shell.

There are three types of tectonic plate boundaries:

  • Plates rip apart at a divergent plate boundary, causing volcanic activity and shallow earthquakes;
  • At a convergent plate boundary, one plate dives (“subducts”) beneath the other, resulting in a variety of earthquakes and a line of volcanoes on the overriding plate;
  • Transform plate boundaries are where plates slide laterally past one another, producing shallow earthquakes but little or no volcanic activity.

Another large-scale feature is a hotspot, where a plate rides over a rising plume of hot mantle, creating a line of volcanoes on top of the plate. National Park Service lands contain not only active examples of all types of plate boundaries and hotspots, but also rock layers and landscapes that reveal plate-tectonic activity that occurred in the distant past.

Plate Boundaries and Hotspot Demonstration

Oreo® cookies are a fun way to demonstrate the three types of plate boundaries and a hotspot. (Modified from “Oregon's Island in the Sky: Geology Road Guide to Marys Peak, by Robert J. Lillie, Wells Creek Publishers, 75 pp., 2017, www.amazon.com/dp/1540611965).

Divergent Plate Boundary

Volcanic eruptions and shallow earthquakes are common where plates rip apart.

divergent plate block diagram and cookie demonstration


Convergent Plate Boundary

Where plates crash together, one dives (“subducts”) beneath the other, causing volcanoes (red triangles) to erupt on the overriding plate and earthquakes (black stars) at a variety of depths. The large white star represents the zone where plates lock together for centuries then suddenly let go, causing the largest earthquakes.

convergent boundary diagram and cookie demonstration


Transform Plate Boundary

Shallow earthquakes and little volcanism occur where one plate slides laterally past another.

transform boundary diagram and cookie demonstration


Hotspot

In places like Hawaii and Yellowstone, a plate rides over a rising plume of hot mantle, causing earthquakes and a chain of volcanoes.

block diagram of hotspot and cookie model of hotspot

Photos and illustrations above modified from “Oregon's Island in the Sky: Geology Road Guide to Marys Peak, by Robert J. Lillie, Wells Creek Publishers, 75 pp., 2017, www.amazon.com/dp/1540611965.


How fast do the plates move?

Look at your fingernails and watch them grow. That will give you an idea of how fast the plates move relative to one another—about a fraction of an inch to a few inches per year! That doesn’t seem like much, but over time it adds up. For example, moving at about 2 inches (5 centimeters) per year, in our lifetime the Pacific Plate moves 10 to 15 feet (3 - 5 meters) past the North American Plate along the San Andreas Fault, a transform plate boundary in California. As Europe and Africa move away from North and South America at about 1½ inches (4 centimeters) per year, the Atlantic Ocean has opened to a width of 4,000 miles (6,000 kilometers) in the past 150 million years!


Figures Used


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Site Index & Credits

Plate Tectonics and Our National Parks (2020)

  • Text and Illustrations by Robert J. Lillie, Emeritus Professor of Geosciences, Oregon State University [E-mail]

  • Produced under a Cooperative Agreement for earth science education between the National Park Service's Geologic Resources Division and the American Geosciences Institute.


Last updated: February 11, 2020

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