Lesson: The Earth is a Changin'Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
Educational Standards :
Learning Objectives (Return to Contents)
After this lesson, students should be able to:
Introduction/Motivation (Return to Contents)
Have you ever wondered why the surface of the Earth looks the way it does today? Does it look the same as it did 100 years ago? Actually, the Earth's landscape is continually being shaped and molded by different forces of nature. Things like water, wind, ice and temperature have all had a hand in making the Earth look the way it does today. These processes are called erosion, which is the wearing away of the Earth by natural processes. There are several different types of erosion: chemical, water, wind, glacier and temperature. (List these on the board.) We are going to learn more about these types today.
Chemical erosion is a reaction that usually involves acid rain. Acid rain is rain that has been polluted by chemicals in the air. These chemicals change the pH of the rainwater and can be harmful to streams, lakes, forests and the animals living there. Acid rain can also be harmful to buildings and decorative statues by breaking away the materials in which the structures are constructed. If you have ever visited Mammoth Cave in Kentucky or Carlsbad Cavern in New Mexico, then you have seen the affects of chemical erosion. Both of these caves were actually carved out of the land by chemical reactions! Engineers are working on acid rain and chemical erosion by creating cleaner burning fuels and machines (e.g., cars) that do not release as much pollution into the air.
Water erosion is perhaps the most familiar type of erosion. Have you ever watched the moving water in a river or stream pull bits of the bank along with it? When water from rivers, streams or even rain, breaks away at bits (or larger chunks) of land while moving over it, that is considered water erosion. Water can wash away valuable nutrients from farmland, but is also responsible for shaping the Grand Canyon in Arizona and Rainbow Bridge in Utah. Engineers attempt to reduce water erosion by directing the flow of water with dams and levees. They also design technologies to measure scouring, which is the water erosion of a stream bed around the supports for a bridge, which has caused many bridges to collapse in the past.
Wind erosion happens when wind blows away the top layer of soil or sand. Some of the tiny particles of sand that are carried away by the wind act like sandpaper, wearing down larger objects as they pass. Wind erosion can create and move entire sand dunes, shape rocks and other structures, and cause dust storms. The Dust Bowl of the 1930s is a good example of the damage wind erosion can cause. Engineers work on developing technologies that will help reduce the effects of wind erosion for farmers.
Glacier erosion is not as common as other types of erosion. A glacier is created by fallen snow that has been pressed into large areas of hard ice on land. These glaciers are slowly being pulled downhill by gravity, and wear away at the Earth's surface as they move. Have you ever ridden on the Matterhorn at Disneyland? The Matterhorn is an actual mountain in Europe that was formed by glacier (ice) erosion. Glacier erosion has caused many large rock formations on Earth, such as Yosemite Falls in California and the Grand Tetons in Utah.
Lastly, you have probably noticed that sidewalks are not just continuous sheets of concrete, but rather have grooves in them. We often call these grooves "cracks" in the sidewalk. Why do you think they are there? These grooves actually help prevent the sidewalk from cracking too much by allowing it to grow and shrink as the weather gets warm and cold. This is called temperature erosion. Temperature erosion can cause metals or concrete to break, such as roads and bridges.
Engineers need to learn about and understand erosion in order to safely design and build structures for people to use and visit. Engineers also learn about erosion to help protect existing land formations and monuments that document our world's history. Civil engineers use their knowledge of erosion to design buildings, roads and bridges in areas that might not have a lot of natural erosion or by using sturdy materials to build them that resist erosion. Environmental engineers plant trees and other plants in order to help prevent wind and water erosion from damaging land. (Plants and trees have ample roots underground that help hold the Earth and soil around them in place.) Engineers also design highways, overpasses and sidewalks in a way that allows them to expand and contract with temperature changes so that they will not crack too much (e.g., the grooves in the sidewalk), remaining safe for their users.
Lesson Background & Concepts for Teachers (Return to Contents)
Erosion is the wearing away of the surface of the Earth by natural processes (weathering, dissolution, abrasion, corrosion, etc.). Chemical, water, wind, glacier and temperature are continually changing the landscape of the Earth.
Chemical erosion involves a chemical reaction (one or mores substances changed into others). Most chemical erosion is the result of acid rain. Acid rain occurs when rain mixes with elements and gasses in the air, specifically pollutants like sulfur oxides and nitrogen oxides. These pollutants come from vehicles, factories and power-generation plants (which burn fossil fuels). See Figure 2 for an illustration of the acid rain cycle. This causes the water to have an acidic pH of approximately 5. (Note: On the pH scale, 7 is neutral (i.e., "pure" water), with any number towards 1 being more of an acid, and any number higher than 7 being more of a base. Visit http://www.epa.gov/acidrain/ph.html for more information.) Wind can then carry this contaminated water hundreds of miles away from the original pollution site, which then harms streams, lakes, forests and any water life which resides there (i.e., frogs and fish, among others). In addition to hurting nature, acid rain also destroys man-made structures, such as historical buildings and monuments. Some other examples of chemical erosion are Mammoth Cave in Kentucky or Carlsbad Cavern in New Mexico (both carved out by this process).
Environmental engineers try to neutralize acid rain by planting trees, as they can have a buffering effect on acid rain. Forests reduce the acidity through the leaching process on leaves and the ion exchange in the soil. Engineers are also working on decreasing pollution by creating cleaner burning fuels and machines (e.g., cars) that do not release as much pollution into the air. Engineers try and protect structures from chemical erosion by using building material that are resistant to acid rain
Water erosion is perhaps the most familiar type of erosion. Water erosion can take many different forms. Sheet erosion is when a fairly uniform layer of topsoil is removed by raindrop splash and run-off during storms. This can cause soil to lose nutrients, which affects the land's ability to produce crops. Rill erosion is caused by run-off water gathering in flow lines (usually on recently cultivated land). It leaves small channels along the soil and often deposits this soil in streams or reservoirs, which can damage the surrounding ecosystem. If rill erosion is not addressed, water will continue to deepen these channels into gullies (gully erosion). Gully erosion results in the loss of significant amounts of land. Tunnel erosion occurs when water removes soil below the Earth's surface. This causes cavities to form underground, which weakens the surface. If these tunnels collapse, they become deep gullies. Tunnel erosion is dangerous because these cavities could collapse at anytime and cannot be detected from above. Stream-bank erosion is caused by moving streams or river water wearing away the surrounding banks. This can drastically change the course of a river and ultimately the surrounding landscape. Shore erosion deposits sediment into the body of water and changes coastline (storms, such as hurricanes, can accelerate this process). Water erosion has also shaped canyons (e.g., the Grand Canyon in Arizona) and rock formations (e.g., Rainbow Bridge in Utah).
Engineers try and minimize erosion by directing the flow of water using dams and levees. Planting grass and trees (to form a strong root system) or laying out netting can also decrease water erosion. Scouring is the erosion of streambed material that supports bridges and has been the cause of disasters and near-disasters throughout the nation. Engineers have developed several systems to measure scouring, including remote sensors and active sonar that monitors stream scouring as it happens. Figure 4 illustrates different types of water erosion.
Wind erosion creates and moves entire sand dunes, shapes rocks and other structures, and causes dust storms. Sand dunes are always being reshaped and shifting due to the wind. Dunes start out as mere ripples in the sand and gradually increase in size. Sand is moved up to the top of the dune until the pile becomes so steep that it collapses and slumps down the other side (the slip face; see Figure 5). Sand dunes are particularly vulnerable to wind erosion because they are completely composed of loose sand without anything anchoring them in place.
Wind erosion also shapes rocks and deteriorates structures, such as the ancient pyramids in Egypt. The wind picks up grainy particles — such as sand — and literally becomes airborne sandpaper that wears away (sands down) surrounding surfaces. The famed Devil's Tower in Wyoming (our nation's first national monument; see Figure 6) was actually created by wind erosion. It used to be a volcano, but now all that remains is the solidified, lava core. (The wind was powerful enough to cut away an entire volcano!)
One of the biggest problems associated with wind erosion is dust storms. The wind picks up dust, leaving crops exposed and blocking out the sun with a big black cloud. Farmers protect their crops (particularly potatoes) by planting larger crops (like rye) surrounding them or covering them with straw and foliage. Figure 7 shows unprotected and protected crops.
A glacier is created by fallen snow that has accumulated and been compressed into massive ice formations on land. They make up about ten percent of the world's total land area. These masses are slowly pulled downhill by gravity, eroding the surface of the Earth as they move. Glacier erosion occurs by abrasion, crushing and fracturing material in the path of a glacier. This moving glacier picks up rock and sand along the way causing their surfaces to become extremely rough, which wears away even more material. Glacier erosion shaped Yosemite Falls in California, created the U-shaped valleys in Rocky Mountain National Park in Colorado (see Figure 8), and formed the Grand Tetons in Wyoming. The Matterhorn, a mountain in the European Alps, was also shaped by glacier erosion. It is unique in that it has four faces (slopes), which face the four compass directions.
Temperature erosion causes materials to crack and break apart. When material such as concrete or steel heats up (from the sun, for example), it expands; when it gets cold it shrinks in size. This fluctuation in size due to temperature can cause the material to crack. (Colorado is an excellent example of a climate where temperature is a problem for materials, since one day it can be 70 degrees and the next day it can snow, and be only 40 degrees outside.)
Engineers have accounted for these changes by putting groves in sidewalks (see Figure 9) and expansion joints in bridges. This minimizes the damage caused by thermal erosion, which is important since broken concrete on the road can be dangerous.
Vocabulary/Definitions (Return to Contents)
Associated Activities (Return to Contents)
Lesson Closure (Return to Contents)
Can you remember the different types of erosion? There is chemical, wind, water, glacier (ice) and temperature erosion. Wow, that a lot of ways that nature can change the surface of the Earth. In fact, some of the coolest natural land formations have developed by a type of erosion. For example, the Grand Canyon was formed by water erosion, sand dunes are formed by wind erosion, and the Matterhorn, a mountain in the European Alps, was caused by glacier erosion. Erosion is a natural process, but humans have an effect on the amount of erosion that occurs sometimes as well. Can you think of how? Well, sometimes we pollute the air, which can cause acid rain and chemical erosion. Also, we build buildings and dams that may alter the natural path of water and wind erosion. Those are just a few ways that we affect erosion. Engineers need to learn about how erosion works in order to help prevent too much of any one type of erosion from occurring. Engineers design and build the schools, skyscrapers and structures where people live and work. They are also involved in protecting existing land formations and monuments that people visit, and therefore, wish to keep standing and in unaltered shape.
Assessment (Return to Contents)
Discussion Questions: Ask a couple of discussion questions to get students thinking about the upcoming lesson. After soliciting answers, explain that these questions will be answered during the lesson.
Voting: Ask a true/false question and have students vote by holding thumbs up for true and thumbs down for false. Count the votes and write the totals on the board. Give the right answer.
Lesson Summary Assessment
Can You Picture It? Show the students pictures of different things that have been affected by erosion and see if they can guess which type of erosion caused it. For example, the Grand Canyon, Carlsbad Caverns, Ayers Rock, the Grand Tetons, Devils' Towers, an eroded statue, cracks in pavement, etc.
Idea Web: Ask students to develop a list of the different types of erosion. What effects does erosion have on us and our environment? What are possible solutions for reducing these effects? What can engineers do to help?
Engineering Poster: Using the knowledge they learned in the lesson on the types of erosion, have students create a poster of a design for a protective structure for a statue or natural landform that would withstand one of the types of erosion (water, wind, temperature, glacier or chemical). Have them title their posters with an engineering firm name that they make up (for example, Erosion Engineering Firm). Have the students work in teams if possible.
Lesson Extension Activities (Return to Contents)
Find some images of your area from 100 years ago to modern day. Have the students compare and contrast the images. What has changed? How much of this change is due to natural erosion? How much is due to human intervention (building and such)? If the area had been left alone except for natural processes such as water, wind and temperature, what parts of the landscape do the students think would have changed over 100 years due to erosion?
Have students investigate the human affect on erosion. For example, can they find examples of human contributions to acid rain, or re-routing of waterways that have affected the surrounding landscape? Have the students develop a plan to help reduce the human effect on the natural erosion that occurs over time. Have them describe activities that they could participate in that would help with land conservation and preservation of monuments or landscapes.
The following website has an activity that uses a video to compare GPS satellite images of locations and describe the natural forces that shape them. This could be a good transition into landforms from erosion. Visit the Discovery Education website at: http://school.discovery.com/lessonplans/programs/earthssurface/ to access the activity.
Students may visit the following website: http://www.ngdc.noaa.gov/seg/hazard/slideset/24/24_slides.shtml to learn about erosional landforms. They should report back to the classroom all that they learned about erosion from the website resource.
References (Return to Contents)
Cavers, Curtis. Manitoba Agriculture, Food and Rural Initiatives, Crops, "Soil Management on Potato Land," March 2006.
City of Longbeach, Public Works Department, Sidewalk Repair Program.
Discovery Education, discoverySchool.com, Lesson Plans Library: 6-12, Earth Science, "Investigating Earth's Surfaces."
The Government of the Hong Kong Special Administrative Region of the People's Republic of China, Education and Manpower Bureau, Science Education Section, Science (S1-3), Unit 5: The Wonderful Solvent: Water, Articles, "Acid Rain, accessed July 25, 2006. http://resources.ed.gov.hk/~s1sci/R_S1Science/sp/en/syllabus/unit5/article-ar.htm
National Geophysical Data Center, NOAA Satellite and Information Service, Natural Hazards, "Erosional Landforms," May 3, 2005, accessed August 1, 2006. http://www.ngdc.noaa.gov/ngdc.html
U.S. Department of the Interior, National Park Service, Parks and Recreation, View All Parks A-Z, accessed July 25, 2006. http://www.nps.gov/parks.html
U.S. Department of the Interior, U.S. Geological Survey, Coasts: Sand and Dunes, "Dunes – Getting Started," January 19, 2004
U.S. Environmental Protection Agency, Clean Air Markets – Environmental Issues, "What is pH?" May 30, 2006, accessed July 25, 2006. http://www.epa.gov/acidrain/measure/ph.html
United States Department of Agriculture, Natural Resource Conservation Service, Erosion, accessed August 1, 2006. http://www.mo.nrcs.usda.gov/news/MOphotogallery/erosion.html
ContributorsTeresa Ellis, Malinda Schaefer Zarske, Janet Yowell
Copyright© 2006 by Regents of the University of Colorado
Supporting Program (Return to Contents)Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
Acknowledgements (Return to Contents)
The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and the National Science Foundation (GK-12 grant no. 0338326). However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.