Plate Tectonics (Danielle Boman)

Student prior knowledge: The movement of the plates creates three types of tectonic boundaries: convergent, where plates move into

one another; divergent, where plates move apart; and transform, where plates move sideways in relation to each other.

Convergent Boundaries: Where plates serving landmasses collide, the crust crumples and buckles into mountain ranges. India and Asia crashed about 55 million years ago, slowly giving rise to the Himalaya, the highest mountain system on Earth. As the mash-up continues, the mountains get higher. Mount Everest, the highest point on Earth, may be a tiny bit taller tomorrow than it is today.

These convergent boundaries also occur where a plate of ocean dives, in a process called subduction, under a landmass. As the overlying plate lifts up, it also forms mountain ranges. In addition, the diving plate melts and is often spewed out in volcanic eruptions such as those that formed some of the mountains in the Andes of South America.

At ocean-ocean convergences, one plate usually dives beneath the other, forming deep trenches like the Mariana Trench in the North Pacific Ocean, the deepest point on Earth. These types of collisions can also lead to underwater volcanoes that eventually build up into island arcs like Japan.

Divergent Boundaries: At divergent boundaries in the oceans, magma from deep in the Earth's mantle rises toward the surface and pushes apart two or more plates. Mountains and volcanoes rise along the seam. The process renews the ocean floor and widens the giant basins. A single mid-ocean ridge system connects the world's oceans, making the ridge the longest mountain range in the world.

On land, giant troughs such as the Great Rift Valley in Africa form where plates are tugged apart. If the plates there continue to diverge, millions of years from now eastern Africa will split from the continent to form a new landmass. A mid-ocean ridge would then mark the boundary between the plates.

Transform Boundaries: The San Andreas Fault in California is an example of a transform boundary, where two plates grind past each other along what are called strike-slip faults. These boundaries don't produce spectacular features like mountains or oceans, but the halting motion often triggers large earthquakes, such as the 1906 one that devastated San Francisco.

Explanation:

After going through the power-point presentation with students, pass out the materials that are needed to do the experiment. Students will be working with graham crackers and frosting to examine the phenomena of plate movement and the changes they can cause in the earth's features.

The first plate boundary the students should experiment with is transform boundaries. The students need to first spread a thick layer of frosting in the middle of the wax paper. The frosting will act as magma in their experiments so they can see what actions the magma takes during the plate motions. The students will lay two crackers down on the frosting, very close together. Once they are placed in the frosting, the students will push them together than slide one cracker away from themselves, and the other towards them. This will create a grinding and it will be difficult to move. This is the fault line that causes earthquakes.

The second plate boundary the students should experiment with is divergent plate boundaries. To do this the students will need to use the plastic knife to scrape as much frosting off the crackers as possible. They will also need to re-smooth the frosting so that there is a clean work surface to begin with. The students need to place the two crackers down close to each other, but not touching. To create a divergent plate boundary, the students need to push-down on the crackers while slowly pushing them apart from one another. This will cause the frosting to come up in the middle and create a rift.

The third plate boundary, and final boundary that the students will be working with is the convergent boundary. The students will once again need to scrape as much frosting from the crackers as possible. The students will use two new crackers for this boundary. The end of both crackers will be dipped quickly in water so that it is a little damp. Once this is done, the students will place the crackers close to one another, but not touching. Then the students will push the crackers together. They will push together in an upward motion forming what looks like a mountain range.

Questions & Answers: Give three thought-provoking questions and provide detailed answers.

1. What is an example of a natural feature of the earth that is an example of a convergent boundary? Why do you believe this?

The Himalayas, a mountain range in Asia is home to the highest peaks in the world. The mountain range is lifted by the subduction of the Indian tectonic plate under the Eurasian plate. The mountain range is rising at a rate of about 5mm per year.

2. What is an example of a natural feature of the earth that is an example of a divergent boundary? What features of the landmark give you clues that it is formed from a divergent boundary.

The Great Rift Valley in Africa is an example of a divergent boundary. The two plates are sliding apart, creating new crust. The valley is lined with active volcanoes. The trench extends almost 6,000 km.

3. What causes earthquakes?

When two plates meet and are pushing on one another they build up pressure. When the plates build up enough pressure they slip or slide past each other. This sends vibrations through the ground and produces the shaking feeling that occurs when there is an earthquake.

Applications to Everyday Life: Explain (don't just list) three instances where this principle can be used to explain other phenomenon.

The information in the lesson can be used to explain three different phenomenon that are directly related to the three different types of boundaries. The transform plate boundaries results in earthquakes. Living in California, many of us are familiar with the feeling of earthquakes and the shaking that occurs.

Convergent plate boundaries are responsible for two different natural landmarks. When two plates collide and the plates go through the uplift process, mountains are formed. If the plates continue to collide, the mountains continue to grow in height. When one plate is sucked under the other (or subduction), the plate is recycled back into the mantle. This is the point at which volcanoes are formed.

Divergent plate boundaries are where the plates drift apart. There is a gap between the two existing plates, which is filled with magma. There is new crust created in this area. The gap between the plates are called a rift or a trench.

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made.