Container for each group (at least 12"x6")
Larger container for demonstration purposes
Glass bottle filled with water (closed)
The previous day, put a glass bottle into the freezer wrapped in newspaper. Also, crinkle up the aluminum foil and place it into the freezer.
Begin by explaining the differences between erosion and weathering. Weathering is the gradual (generally) breakdown of rock. Ask the students how this might occur. Normally, this is due to people, animals, plants (through root development), and frost wedging. To explain frost wedging, pull out the glass bottle and explain that water expands when it freezes. Be careful when you unwrap the bottle, since there will probably be loose shards of glass. Next, explain that erosion is the movement of weathered soil. Ask students how erosion might occur. Normally this happens when water (rivers, rain, and tides), wind, or ice (glaciers) "grabs" onto the loose particles and transports them.
How powerful is air?
Place some sand in the large container. Ask the students if wind is a powerful force in erosion (most will say yes since tornadoes quickly come to mind). Next, turn the hairdryer on very low. Only a few particles of sand should move each second. Tell the students that most winds move at approximately that speed. Ask the question again (most will change their minds). Now turn the hair dryer on high so that almost all of the sand is moved. Explain that wind is a powerful form of erosion and that even at slow speeds (a few grains per second) mountains can get eroded over millions of years. If you have pictures of badlands formations, let the students see some of the results of wind.
Water, water, everywhere...
Water comprises the majority of the earth. Ask the students to explain how water can become an important erosional force. Explain that water can move sediment through rivers, rain, and tides. If available, show a picture of the Grand Canyon or some other dramatic example of river erosion. Show pictures of tidal erosion on coastlines or mudslides in California. Next, ask the students whether or not the speed of water has an effect on erosion. For example, does fast moving water move more sediment than slow moving water? Make two mounds with the topsoil. For the first mound, hold the cup of water 2" above the soil when you pour. Make sure the students see how much sediment is being carried. Next, hold the cup 12" above the topsoil and pour. Notice that much more sediment is moved.
Ice a MILE thick?
In Michigan, we have glacial evidence everywhere. During the last ice age, the glaciers were approximately a mile thick in places. Pull the aluminum foil out of the freezer. Flatten out a long piece of Play-doh. Have one of the students pull the piece of frozen aluminum foil across. Notice the scour marks. Explain that some of the glaciers moved boulders larger than cars. Further, these gouges can be found throughout the Keweenaw Peninsula. An obvious one (for those interested) can be found on the playground at Calumet High School.
Now that the students understand what erosion and weathering are, have them compete in a little contest. Break the students down into groups of 3-4. The object is to have each group create a "mound" that must stand up to erosion (wind and water). Allow the students to choose from (using any or all of one type) topsoil, sand, and small pebbles. Once the students have built their indestructible mounds. submit each to the blow dryer and a cup of water. Very few will be left standing.
A real-world problem
When the contest is over, explain to the students that what they did today is a problem that is dealt with on a worldwide basis. Environmental and civil engineers have spent millions of dollars and hours trying to prevent erosion from occurring. Planting trees and grass, building break walls and jetties in lakes and oceans, and constructing walls and reinforcing the sides of mountains along roads are all attempts to prevent erosion from modifying the landscape.
Shawn Len, 2000.