EROSION BY WIND AND ICE
Our landscape is shaped by erosion. Wind and ice erosion are two main types of erosion that occur in extreme heat or extreme cold. Different types of wind and ice erosion are discussed in this activity.
To teach students about ice and wind erosion.
Students will be able to:
- Explain the difference between weathering and erosion.
- Describe at least two physical weathering processes.
- Describe at least one chemical weathering process
Set up: 10 min.
Activity: 30 min.
Discussion: 20 min.
- 5 lb. block of ice
- Paper punch holes
Rocks break down from large pieces to smaller pieces by physical and chemical processes. When these processes change the rock's size in place it is called weathering. When rock pieces break down and transport away, it is called erosion.
Physical weathering and erosion occur when large pieces of rock are broken into smaller pieces without changing the rock composition. This is known as a physical change. An example of a physical change is when you hit a rock with a hammer and it breaks into smaller pieces. Resulting pieces are still the same rock type but their size has changed.
Chemical weathering and erosion occurs when rock is changed into smaller pieces by chemical processes. This is known as a chemical change. Resulting rock is not the same as the original. For example, if acid is poured on chalk (CaCO3) it will fizz. Gases (CO2) are given off and the remaining rock piece is calcium (CaO). The chalk composition changes due to the chemical reaction. The rock changed to a different chemical composition.
Wind action physically erodes and creates landforms. Wind is a form of thin liquid that transports small pieces of rock. This kind of erosion is not very strong. Wind takes a lot of energy to transport sand and dust. This type of erosion is known for smoothing and rounding landscapes. This occurs as sand and dust impact into larger rocks like small torpedoes. Each impact can break off small pieces of the larger rock, leaving them in place. Sometimes the torpedoed grain explodes into smaller pieces. Resulting debris on the larger rock stay in place and wait for stronger forces, such as water, to transport them away.
Ice is a force that causes great amounts of physical erosion. As glaciers flow down slope, their weight presses into the hillside and gouges out the rock. During flow the glacier also melts and refreezes along the ice/rock contact, picking up rock pieces and incorporating them into the ice block. Once rock pieces are picked up by ice, they are dragged over other rocks and they break into smaller pieces. There is little chemical erosion by glaciers.
Solufluction is the downward movement of rock particles by the combination of ice and gravity. In tundra locations in the world the soil is commonly frozen together with ice crystals. Crystals grow and push the rock particles apart. When they melt soil particles move slightly down slope. When water freezes again it moves the particles away from each other and the process repeats itself. If the process occurs many days in a row, a hillside may form wrinkles on the surface like the top layer of soil is sliding down hill.
Another form of slow downhill movement is creep, as in 'creeping along'. Creep is caused by gravity alone. Hillslope particles give way to gravity and slowly fall down slope. This process is extremely slow and would be difficult to see without a lot of time and measurements.
Living organisms also erode the landscape. For example, plants that push their roots into cracks break the rock into smaller pieces as they grow. This kind of physical erosion is called root wedging. Plants also take minerals they need from the rocks, changing the chemical composition surrounding the roots. This is a chemical change. Plants can also help hold rock in place. Roots grow intertwined, forming a web in areas and do a good job of trapping and keeping the rock in place. This is why road cuts along a freeway are reseeded as quickly as possible.
Animals cause both chemical and physical erosion. When animals dig up dirt they expose it to the air and water, which causes chemical reactions. They also do a good job of pushing dirt downhill. Human interference, such as driving off designated roads and trails, causes erosion in new paths by destroying a soil crust or plants holding the soil in place. Walking off trails, which forms new trails, will hinder plant growth and allow erosion to take over the exposed ground.
The following activities provide students with firsthand experiments showing glacial, wind and creep erosion.
- Place block of ice on the ground outside. Have a student sit on the block and another student push the block slowly across the ground. Remember glaciers move slowly down hill because of their weight.
- Every five feet look at the bottom of the ice block. Observe and record what the ice has picked up and what has been pushed out of the way or ahead of the block.
- Repeat with different ground surfaces, including grass, sidewalk, sandbox, etc.
- Observe what has happened to the particles that have been picked up by the ice. Record the changes in the surface the ice has slid upon.
- Take a cup of sand and spread it on a flat surface about 2 millimeters thick. Take a pile of paper punch holes and spread them out on the same flat surface. Roll the piece of paper to form a funnel large enough to cover the entire fan.
- Aim the funnel at each spread, changing the diameter of the hole and determine which transports more particles. Explain that grain size and shape determines how much energy it will take to move a particle. Also explain that changing the diameter of the hole changes the energy exposed to the two spreads. Explain to the students that wind erosion take a lot more energy to change a landscape than water, ice and gravity erosion.
- Blow up all the balloons.
- Place two tables or desks on end next to the wall.
- Place a beach ball between the desks semi inflated with the hose of the pump still attached.
- Pile the rest of the balloons on top of the beach ball. Inflate and deflate the beach ball showing how the shrinking and swelling of the ball causes the balloons to settle. The growing and deflating of the ball is what happens to water crystals and the movement of balloons are the rock particles on the hillslope.
What is a glacier? What happened to the different surfaces our "mini-glacier" was pushed over? What got pushed away? What got picked up? What do all the pieces look like? Is this an example of erosion or weathering (both)? What kind of weathering is it (physical, mostly)? Did glaciers ever come through this area that we live in? If yes, find some evidence in your local community of glacial weathering and erosion and show it to the students. How much stuff was moved by small gusts of wind? Can large boulders move due to wind? What is creep? How much erosion is caused by creep? What causes creep?
Have students research National Park Service Sites to find examples of each of these processes. Have them present their findings to the class and defend their position as to why each NPS site presented is a good example.
Included National Parks and other sites:
Utah Science Core:
2nd Grade Standard 6 Objective 1, 2, 3
5th Grade Standard 1 Objective 2, 3
5th Grade Standard 2 Objective 1, 2, 3