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Lesson Plan

Mountain Building

Florissant Fossil Beds National Monument

Grade Level:

Upper Elementary: Third Grade through Fifth Grade

Subject:

Science

Lesson Duration:

60 Minutes

State Standards:

Colorado Academic Standards for Science
3.2.a - Identify how forces change Earth’s surface
3.2.b - Explain factors that change Earth’s surface

Thinking Skills:

Understanding: Understand the main idea of material heard, viewed, or read. Interpret or summarize the ideas in own words.

Essential Question

How are mountains formed?

Objective

Students will learn how tectonic forces form mountains and valleys. They will also learn to distinguish between compressional and extensional forces.

Background

There are two types of tectonic forces that can create mountains and valleys: compressional and extensional. At a convergent boundary, or compressional environment, two continents collide and rock layers undergo buckling and folding. The buckles and folds form mountains and valleys. In rock, the buckles can fracture and slide on top of each other. In this situation the rock behaves in a brittle fashion. If the rocks simply fold and don’t break, we call that ductile behavior. A modern day example of a compressional region is the Himalayan Mountains in India. When India collided with Asia millions of years ago, the Himalayan Mountains began to form and continue to grow today, as the plates are pushed together.

In a divergent boundary, or extensional environment, stretching of the continent causes it to thin and break. From this, faults form and allow large blocks of rock to either move up or down relative to one another. The blocks of rock are called fault blocks, which are divided into two categories: horsts and grabens.

Here in Colorado, we have both extensional and compressional forces that have shaped the Rocky Mountains as we see them today. The Laramide Orogeny (mountain building event) is an example of compressional forces that produced folding and uplift of many of the rocks we see in the Rocky Mountains. The Rio Grande Rift is an example of extensional forces that has produced mountains (Sangre de Cristo Mountains) and valleys (town of Buena Vista) in the Colorado Rocky Mountain region.

Preparation

You will need:

• A beach or bath towel

• 4inch x 6inch index cards (3)

• Pencil or pen

• Ruler

• Tape

• A table

Lesson Hook/Preview

The movement of tectonic plates generates forces that can create mountains and valleys through either compression or extension. In this activity you will show how these forces work and form these geographic formations.

Procedure

A convergent boundary is where two continental plates collide and rock layers buckle and fold. This is where compressional forces are at work. The buckles and folds form mountains and valleys as the plates push against each other. Sometimes the buckling layers fracture and slide over each other. We then say that the rock is behaving in a brittle fashion. If the rock doesn't break and keeps warping and folding we say that if is showing ductile behavior.

#1: Fold your towel in half twice; once vertically and again horizontally. Lay it on the table so you can see each “layer” of the towel (the edges rather than folds).
#2: Place a hand on either end of the towel. Slowly move your hands towards each other sliding the ends of the towel together. Watch as the middle folds upward.

This is how mountains are formed by compression at a convergent boundary.You can see how each layer of the towel has warped and folded over each other. As two plates push against each other the rock layers may fold like the towel did. As you drive through mountains you may see outcrops or road cuts showing how the layers of rock folded.

A good example of mountains being formed by compression is the Himalayan Mountains in India. When India crashed into Asia millions of years ago at a convergent boundary, the Himalayan Mountains began to form. The Indian and Asian continental plates are still pushing against each other, so the mountains are still growing!

A divergent boundary is where a continental plate is stretching making it get thinner and break. This is the work of extensional force. As the rock layers thin and pull apart, faults form letting large blocks of rock move either up or down in relation to each other. These blocks are called fault blocks and can be categorized as either horsts or grabens. A horst is a block that moves up. A graben is a block that falls down.

#3: Take an index card and measure length-wise 1inch and mark it with a pen or pencil. Measure four more sections marking each one in order: 1 inch, 1&1/4 inches, 1 inch, 2&1/4inches, and 1/2 inch. Draw vertical lines to mark each section.

#4: Take another card and measure and mark sections: 1&1/4 inches, 1 inch, 1&1/4 inches, 2 inches, and 1/2 inch. Draw vertical lines to mark each section. Do the same to the third card.

#5: Fold the card and make a crease along each line on all three cards.

#6: On one of the folded cards, glue the outer side of the 1/2 inch section to the inside of the opposite edge to make a block. Do the same with the other two cards so that you have three blocks.

#7: Place two of the blocks side by side with the wide side down and their edges touching. Place the third between the two blocks with the short side down. The two bottom blocks should hold up the third block. Try to get their tops even with each other.

#8: Pull the two bottom blocks away from each other. The block resting on top of them should slide down.

This is an example of extensional forces making mountains. The middle block that moved down is the graben. The other two blocks with their tops higher are the horsts. Can you see how this created two "mountains" and a "valley" between them?

The Rio Grande Rift is an example of extensional forces that created the Sangre de Cristo Mountains and valleys such as the town of Buena Vista in the Colorado Rocky Mountain region.

The Rocky Mountains in Colorado have been formed using both compression and extension. The Laramide Orogeny (a major mountain building event) involved compressional forces that led to folding and uplift of many of the rocks found in the Rocky Mountains today. 

Vocabulary

• Tectonic: adjective; of or relating to tectonics

• Compression: noun; the act, process, or result of compressing or pressing

• Extension: noun; the act of extending or stretching

• Orogeny: noun; a process where a section of the Earth's crust is folded and deformed by forces of compression and creates a mountain range

• Graben: noun; a block of the Earth's crust sitting between two faults that drops down relative to the blocks on either side of it

• Horst: noun; a block of the Earth's crust sitting between two faults that rises up relative to the blocks next to it on either side

• Hanging Wall: noun; a block of the Earth's crust that sits on top of a fault (if you stood on the fault with a lantern and you wanted to hang it, you would hand the lantern on the hanging wall)

• Footwall: noun; a block of the Earth's crust that sits below a fault (if you stood on a the fault with a lantern, your feet would be on the footwall)

• Fault: noun; a break in the Earth's crust accompanied by a displacement of rock masses parallel to the break

• Normal Fault: noun; a fault where one block (the "hanging wall") moves down relative to the opposite block (the "footwall")

• Reverse Fault: noun; a fault where one wall (the "hanging wall") moves up relative to the opposite block (the "footwall")

• Transform Fault: noun; a fault where two blocks move in opposite directions horizontally rather than up or down

• Ductile: adjective; able to be deformed without losing strength; pliable

• Brittle: adjective; easily broken, cracked, or snapped

Assessment Materials

Reflection

Ask the students, was there faulting in the first example of compressional forces (colored foam sheets)? Why or why not? Explain to them that the towel model represents ductile material, whereas the index card blocks represent brittle material. From here, go into further detail as to how in the field geologists find folded rocks that can be faulted (broken) and/or ductile (intact). Ask the students again; what are the different forces that build mountains? How do they work? Are there any mountains here? If so, do you know how they formed? Can we ever feel mountains moving? What do we call the shaking when we feel there is movement of the Earth’s crust? Share with the students that the Rocky Mountains of Colorado exhibit mountain building through both compressional (e.g., initial development of the mountain ranges) and extensional forces (e.g., San Luis Valley).

Rubric/Answer Key

Compression and extension forces both can build mountains from plates either pushing together or pulling apart. Earthquakes are caused by the movement of the Earth's crust.

Additional Resources

Check out our other Mountain Building activity webpage for step by step instructions with pictures!

Contact Information

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