- Grade Level:
- Middle School: Sixth Grade through Eighth Grade
In this classroom activity, students learn about the Mantle Plume Theory, plate tectonics, and Idaho geography by experimenting with a map of Idaho.
The theory of plate tectonics explains much of Earth's geology. For example, California's famous San Andreas fault is formed where two tectonic plates come together and slide by each other. The tension that is created along the fault is periodically released, like a rubberband stretched to its breaking point, resulting in earthquakes. Other geologic phenomena require a combination of theories to be explained. For example, events creating the Snake River Plain that stretches across southern Idaho from Oregon to Wyoming cannot be described as easily as the San Andreas fault. A combination of rifting, basin and range faulting, the mantle plume theory, and plate tectonics are required to explain that big crescent. For a concise description of these theories and the likely sequence of events that made the Snake River Plain see Geology for Teachers. The student activity that follows will require that teachers understand the basics of these theories.
- Students will be able to explain the basics of the mantle plume theory.
- Students will understand that the crust slides over the mantle.
- Students will be able to name key cities and geologic features of Idaho.
- Student Worksheet for each student
- Magic marker or highlighter for each student
- flashlight for teacher
- Small nougat filled candy bar for each student who completes the map (optional)
- Reference maps of Idaho and neighboring states
- Geology for Teachers
- Teacher's Answer Key
Part 1: Demonstrate Rifting
Show the students the blank map (student worksheet), a copy of which they will soon receive. Emphasize that if Idaho were really this big, the crust would be about the thickness of the paper. Idaho is part of a massive piece of crust called the North American Plate and it slides as a unit over the Earth's mantle.
With the Idaho map you will demonstrate the mantle plume theory, rifting, and plate tectonics. The students will then repeat the demonstration on their own maps individually and in teams, adding information to their maps as they work.
The ground beneath our feet in Southern Idaho is being stretched in an east to west direction. On the Eastern Snake River Plain beginning 15,000 years ago the crust was pulled apart, resulting in lava welling up to the surface. This deep tear in the earth, known as the Great Rift, runs 50 miles north-south and is over 600 feet deep in some areas! Locate the line through Craters of the Moon on your map that represents the Great Rift. Punch pencil holes along the line and tear slightly to demonstrate the rifting here.
As another way of demonstrating the process you may give each student a Snickers bar and let them pull and twist it to create faults and fractures before they eat it. You may wish to do this at the end of the class. Perhaps the Snickers bar could be used as a reward for demonstrating their knowledge to you about the formation of the Snake River Plain and geography of Idaho.
The Western Snake River Plain consists of a large fault-bounded block known as a graben. This graben has been subsiding for thousands of years has gradually filled with older lava and sediments.
Part 2: Demonstrate Mantle Plume Theory
Let the candle represent a hot spot in the mantle. Geologists think this heat source may have nuclear origins, like the heat generated in a nuclear reactor (it represents no threat to life because it is buried deep in the Earth). If you did "The Earth, from Core to Crust" activity you might want to get one of the models out to demonstrate the Mantle Plume Theory. Imagine some of the deep mantle material squeezing upward toward the surface in a "plume." That hotter, deep mantle rock creates the heat necessary for the volcanic activity expressed at the surface.
Light the candle to symbolize the hot spot. Hold the crust (your map of Idaho) over the stationary candle high enough so that it won't scorch. From the Geology for Teachers reading you now know that the mantle plume theory applies only to the Eastern Snake River Plain and that 10 million years ago the Plume was located under what is now Twin Falls. You also know that the North American Plate has crept southwest over the eons and that 600,000 years ago the plume or hot spot last erupted to form Yellowstone.
As you describe this to the kids, lower the Twin Falls area to just the point of scorching and slowly move the crust (the map) southwest to form the Eastern Snake River Plain between Twin Falls and Yellowstone. You or a student can say, "10 million years ago, 9 million years ago," and so on as you slowly move the paper over the candle toward Yellowstone so that by the time you get there you're at "one million years ago." Let the scorching paper represent the creation of the Eastern Snake River Plain.
Part 3: Student Maps
Issue your students copies of the provided maps. Have them label their maps with the following to improve their knowledge of Idaho geography. Then they should create the Western and Eastern Snake River Plain and the Great Rift (have them use a marking pen or highlighter instead of a candle for demonstrating the Mantle Plume Theory. Make sure they hold the pen stationary beneath the moving crust and count backward slowly from 10 million years ago until they arrive at Yellowstone).
|Directions||Rivers and Places|
|East||Yellowstone National Park|
|West||Craters of the Moon Nat'l Monument|
|North||Grand Teton National Park|
|Towns and Cities||Western Snake River Plain|
|Arco||Eastern Snake River Plain|
|Idaho Falls||States and Countries|
Make sure the students understand that the above geologic processes happened concurrently over millions of years and that this explanation is a simplified version of reality.