Activity 1: Crustal Types

Lyle Hercularis



The crust of the Earth is divided into plates that move relative to one another. The interaction of these plates creates many of the earth's landforms. Provided information about crustal characteristics and plate boundaries, students will experiment with representative materials to understand crustal interactions.

Instructional Method: Experiment

Goal: Expose students to different crustal types and their interactions.

Objectives: Students will be able to:

  • List the three types of plate interactions.
  • Draw the three interactions.
  • Name one landform that results from each plate interaction.


Setup: 20 mins.
Experiment: 20 mins.
Discussion: 20 mins.

Materials Needed:

  • old cake pan
  • paraffin wax
  • heat source
  • knife
  • clear plastic container
  • water
  • napkins
  • foam and cardboard strips 4 inches wide, 8 inches long
  • markers
  • paper
  • chalkboard




We are most familiar with the layer of the earth called the crust. It is the layer we live on. Surprisingly, it is the thinnest of Earth's layers. The crust ranges in thickness from 5 to 100 km, yet it represents less than 0.1% of the total volume of Earth! The crust is ridged and brittle, and when it cracks or moves, earthquakes occur. The two crust types are continental crust and oceanic crust.

Continental crust is about 35 to 100km thick. It is thickest beneath mountain ranges and plateaus. Continental crust is much lighter, or less dense, than oceanic crust. It contains a large portion of quartz material (SiO2), also known as felsic material.

Oceanic crust is the rock found below the world's oceans. It is the thinner, about 5-10 km thick, and more dense. It is composed of mafic (iron- and magnesium-rich) rock such as basalt. Because oceanic crust is more dense it tends to sink below the lighter continental crust when the two crust types collide.

On Earth the crust is fragmented into a dozen or more large and small regions known as plates. A single plate can be made of both continental and oceanic crust. These plates move relative to one another as they ride atop hotter, mobile material.

Moving plates create and destroy landforms such as mountain ranges, basins, trenches, and deep-sea ridges. Places where different plates touch, and sometimes collide, are called plate boundaries. There are three types of plate boundaries:

  • continental crust to continental crust
  • oceanic crust to oceanic crust
  • continental crust to oceanic crust

Each boundary can be classified in one of three ways:

  • divergent
  • convergent
  • transform

Divergent boundaries form when plates break and spread apart from one another. This occurs when a convection current develops below the crust. Upwelling hot magma forces plates to spread as the magma oozes through cracks at the surface, creating new crust. The place where new oceanic crust is formed is called a spreading ridge. An example of a spreading ridge is the Mid-Atlantic Ridge at the bottom of the Atlantic Ocean.

Divergent boundaries are not found only in the ocean. Sometimes a continental plate will tear apart due to the same upwelling forces that tear apart oceanic plates. For example, Lake Superior is believed to be the remnant of a failed continental rift. That rift did not succeed in tearing the continent into two separate pieces, but it did create a valley that is now filled by water.

Sea floor spreading example

Convergent boundaries are found where two plates collide. Large scale examples of this are seen when continents collide. When plates collide they buckle like the hood of a car in a head-on collision, forming huge mountain ranges. The mountains of Denali National Park are the result of continent - continent collision.

When continental and oceanic crusts collide, heavier oceanic plates slide under lighter continental plates. This process is known as subduction. As it slides below the continental crust, sinking deeper into the hot mantle, the oceanic crust begins to melt. This melted oceanic crust becomes less dense (because it is now in a liquid form) and therefore rises towards the surface causing continental crust to rise up above it, forming mountains and volcanoes.

Mountain ranges formed near subduction zones include the Andes, the Cascades and the Aleutian Islands in Alaska. The Andes formed as the Nazca Plate was subducted below the South American Plate. The Cascades and the Aleutian Islands are forming as the Pacific Plate slides under the North American Plate.

Deep underwater trenches form where continental and oceanic crusts collide. A trench is a depression in the sea floor that can be over a mile deep and hundreds of miles long. When oceanic crust collides with oceanic crust one plate subducts and begins to melt. The melting plate rises towards the surface and can push through the above plate forming underwater mountains and volcanoes. Volcanoes produced from oceanic-oceanic collisions can result in island chains. The Marianas Islands were produced from an oceanic-oceanic collision.

Subduction example

Transform boundaries form where two plates collide and slide next to each other along a fault instead of uplifting or subducting. A famous example of such a collision is the San Andreas fault in California. The thin strip of California to the west of the fault rides with the Pacific Plate as it slides along the side of the North American Plate. The San Andreas is very active, and this constant movement results in frequent earthquakes. Point Reyes National Park in California preserves the beauty associated with fault movement.

The following activities can be used to explain different crustal types, interactions between them, and fault boundaries.

Instructional Procedures:


I. Subduction example:

  1. Fill a clear plastic or glass container with water. Container should be at least 10 inches deep and wider than a paper towel for best results.
  2. Float a paper towel (like those from the bathroom) on the surface of the water.
  3. Carefully, using your finger, dip one end of the paper towel under the surface of the water.
  4. The paper towel should start to sink, or "subduct", similar to the action of a sinking oceanic plate.

II. Sea floor spreading example:

  1. Fill an old cake pan with wax (about 1 to 2 inches thick) and heat over a hot plate to melt the wax.
  2. Bring the wax to a temperature that allows for a thin, cooled film of wax to form on the surface. This represents the earth's crust.
  3. Using a sharp knife, cut a spreading ridge in the center of the pan, above the heat source. Cutting a simple straight line will demonstrate the action at a spreading center. Cutting a zigzag pattern using horizontal lines connecting vertical lines will demonstrate a spreading ridge where both divergent and transform boundaries are found. This is closer to real-life than a simple straight cut.
  4. The wax "plates" should begin spreading due to upwelling convection currents of warm wax from below. If there is little motion in the "plates", try separating the "plates" from the rest of the wax by cutting simple straight boundaries to separate the "plates" from the excess "crust".


Ask students to describe the two types of crust. Which one is thicker? Which one is heavier? How do those differences affect the landforms we see on Earth's surface? What types of landforms result from different plate interactions? What happens when a subducted plate starts to melt? Why do plates move? What is convection?


The following variation is much less complicated and allows students to perform the plate interactions with foam and cardboard. This variation will help students visualize different plate boundaries with foam pieces.

  1. Give foam pieces to each small group or pair of students. There should be either two thick foam pieces labeled "continental crust", two cardboard pieces labeled "oceanic crust" or one "continental" foam and one "oceanic" cardboard. These foam pieces represent plates floating on the mantle (or table, in this case).
  2. Have students move the strips along the top of the table simulating the three types of plate interactions: colliding (convergent boundary), pulling apart (divergent boundary) and sliding next to each other (transform boundary).
  3. Students then draw pictures of how the foam pieces interact and label the types of interactions.
  4. After the interactions are noted, have students exchange pieces of foam to have different plate interactions; continent-continent, continent-ocean, ocean-ocean.
  5. You may want to diagram the interactions on the board for the students before starting the activity.


Have students draw a step by step cartoon of how Oceanic and Continental crust interact. Label each frame with an explanation of landforms and interactions resulting from the collision.

Included National Parks and other sites:

Aniakchak National Monument and Preserve
Bryce Canyon National Park
Denali National Park
North Cascades National Park
Point Reyes National Seashore


Paunsaugunt Fault near Bryce Canyon

Utah Science Core:

5th Grade Standard 2 Objective 1,2,3


Last updated: February 24, 2015

Contact the Park

Mailing Address:

P.O Box 640201
Bryce, UT 84764


(435) 834-5322

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