Mountain Building

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.

You will need:

• A beach or bath towel

• 4inx6in index cards (3)

• Ruler

• Pencil or pen

• Glue

• A table

Instructions

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 rock layers can 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 they are showing ductile behavior.

 

Folding the towel in half two times.

Florissant Fossil Beds National Monument

Step One:

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 the folds).

 

Pushing the ends of the towel in towards each other.

Florissant Fossil Beds National Monument

Step Two:

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.

 

The towel starts to crinkle and fold.

Florissant Fossil Beds National Monument

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

 

The towel has folded over itself creating a bulge like a mountain.

Florissant Fossil Beds National Monument

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 to move either up or down in relation to each other. These blocks of rock 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.

 

The card is divided into measured sections.

Florissant Fossil Beds National Monument

Step Three:

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&1/4 inches, and 1/2 inch. Draw vertical lines to mark each section.

Step Four:

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.

 

Folding along the lines to crease each section.

Florissant Fossil Beds National Monument

Step Five:

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

 

Gluing the ends of the card together to make a mountain building block.

Florissant Fossil Beds National Monument

Step Six:

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.

 

Blocks are set up showing level ground on the top.

Florissant Fossil Beds National Monument

Step Seven:

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.

 

The middle block drops creating a valley between two mountains.

Florissant Fossil Beds National Monument

Step Eight:

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 grabben. The other two blocks are the horsts. Can you see how this created two “mountains” and a “valley”?

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.

New Words!

• 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 out

• 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

• Basin and Range: noun;

• 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 a fault with a lantern and wanted to hang it, you would hang the lantern on the hanging wall)

• Footwall: noun; a block of the earth’s crust that sits below a fault (if you stood on 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 block (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

 

Lesson Plan

Lesson Plan for Mountain Building Activity