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.
1. Demonstrate Rifting
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.
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.
3. Students 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.