Weathering,+Erosion,+Deposition+6-8

Lesson Objectives

By the end of this lesson, students should be able to:
 * Distinguish between mechanical weathering, chemical weathering, and erosion.
 * Identify the agents of mechanical weathering.
 * Distinguish between the agents of mechanical weathering (ice, water, wind, plants, etc.) and the processes of mechanical weathering (abrasion, pressure).
 * Identify how landforms are shaped by the agents of mechanical weathering.



Engage: Activate Prior Knowledge; Generate Interest


 * Activate Prior Knowledge**

Open the session by leading a brainstorming session around the question, “What are the different ways that rock on Earth’s surface can change?” As students give answers, write those answers on the board, sorting them into three unlabeled columns—one for mechanical weathering, one for chemical weathering, and one for erosion. (Don’t tell students why you are placing their ideas into columns yet.)

Show students the video segment Weathering (0:00 through 1:28) to help them to distinguish between erosion, chemical weathering, and mechanical weathering. Before they view the video, tell students that they should write down the definition of erosion that is given in the video. (The definition given is incorrect because it states that erosion is the transportation of the weathered materials; in fact, erosion refers only to the removal of weathered materials. Later in the lesson, students will identify the error in the definition and propose a more accurate definition.)

After the video is over, ask students to identify which columns should have the headings “Mechanical Weathering,” “Chemical Weathering,” and “Erosion.” Now that they are aware of these categories, have them suggest additional ways that rock on Earth’s surface can change. Then have students recall the image of the pothole. Next, ask students to explain how they think that potholes can form, how physical forces can break up roads, and how these processes are similar to or different from those that change rock.

Stimulate Interest

Show students the video segment Weathering to introduce them to the idea that Earth’s surface is constantly built up by mountain-forming processes, and worn down by erosion and weathering. Students will also be introduced to some of the main agents of mechanical weathering—ice, wind, and water. Ask students to hypothesize about how Earth’s surface might look if mechanical weathering did not occur.

Explore: Allowing Students to Experience Content

Post the Essential Questions that constitute what students will be learning. Students may read them to themselves or you may wish to read them aloud together.


 * What is the difference between weathering and erosion?
 * What is the difference between mechanical and chemical weathering?
 * How do water and ice cause mechanical weathering?
 * How does the movement of air cause mechanical weathering?
 * How are rocks and landforms changed by mechanical weathering?

As students view the video resources in this session, have them fill in a table with information about mechanical weathering, including the agents, processes, and their impact on landforms. A sample chart is shown below.

Have students watch and take notes on the first fifty-eight seconds of the video segment Weathering. Tell students to note the different causes, or agents, of weathering as they watch (water, ice, wind, and temperature changes). Then show students the first fifty-eight seconds of the video segment Forces That Shape the Earth: Mechanical Weathering and tell them to pay attention to how mechanical weathering can occur due to the pressure exerted by ice. [Note that lichens attached to rocks are shown in the video as the narrator describes the fragmentation of rock by plant roots. In fact, lichens are not plants and do not have roots. Lichens are typically combinations of algae and fungi, and are significant agents of chemical weathering but not mechanical weathering.] Once students have viewed both videos, discuss as a class the points they were supposed to note as they watched the videos.

Ask students to predict how the physical properties of water change when it changes from a liquid to a solid. For each prediction, have students further predict how that change from liquid to solid might cause rocks in the area to weather. Then show them the video segment [|Physical Weathering] and have them discuss whether their predictions were accurate.

Have students take notes on the first two minutes and three seconds of the video segment Water & Weathering to introduce them to the concepts of ice wedging and abrasion. As they watch, have students write down answers to the question asked at the beginning of the video, “How do weathering and erosion work together to reshape the landscape?” After they have watched the video, encourage students to discuss the answer to this question.

Next, have students watch the video segment Erosion by Glaciers. Before they view the video segment, ask them to hypothesize about the different ways that abrasion can occur. After they watch the video, have students discuss how abrasion actually occurs and compare the processes of abrasion and ice wedging.

Have students watch the video segment [|Forces That Shape the Earth: Wind] and ask them to describe two ways that wind contributes to mechanical weathering. Then ask them to write a paragraph that explains why the lower parts of rock outcroppings are more rapidly weathered by sand blasting than the parts that are higher up. When students have finished writing, collect their paragraphs or discuss the answers as a class to ensure student understanding. (Note: these paragraphs may be assigned for homework.)

Hands-On Activity Have students complete the Hands-On Activity Mechanical Weathering: Which One is Strongest?.

Explain: Firm Up Understanding; Allow Students to Explain What They Know

Review the main agents of mechanical weathering—water, wind, ice, and plants—by having students watch the video segment Erosion from 4:20 to 5:50. After each location is shown, pause the video and ask students to discuss how water, ice, or wind may have shaped the landforms shown.

Next, have students recall the definition for erosion that they wrote down based on the video segment Weathering in the Engage in Session 1. Challenge students to spot the error in the definition of the term erosion and ask them to describe how they would change the narration to more accurately define this term. Then ask students to describe the differences between erosion and mechanical weathering in their own words.

Explore: Allowing Students to Experience Content

Review sub-concepts by having students complete the Exploration Forces That Shape the Earth. As they go through the Exploration, have students create a chart such as the one shown below that identifies the agents and processes involved in creating the landforms shown in the left column. The middle and right columns have been filled in with sample answers. Encourage students to add other examples to the table that were not included in the Exploration. Collect the charts or construct a master chart in order to ensure student understanding

Elaborate: Allow Students to Apply What They Know

Have students extend their understanding of how erosion by wind and water create landforms by watching the video segment Erosion. Have students write a short essay describing how mechanical weathering and erosion work together to change Earth’s surface. Encourage students to include a description of how the slope of the land affects the power that erosion and mechanical weathering can have.

Then have students watch the video segment The Ice Ages to explore how the degree of erosion by glacial processes was more intensive during the last glacial period. Have students discuss why recently-formed glacial landforms would not be present near the equator. Encourage them to discuss the role that differences in climate plays in the types of mechanical weathering that occur in a given region.

Have students read the second page of the passage [|Sculptures of Sand & Stone] to explore how landforms such as hoodoos, glacial valleys, and rock pedestals form. Encourage students to share any experiences they may have had in viewing such landforms (including seeing images of them in movies, magazines, etc.) and to speculate on how they might have been impacted by mechanical weathering.

Finally, have students explore how the Grand Canyon and Big Sur landforms were created by the combination of agents of mechanical weathering and the process of erosion by watching the video segment Erosion. As they watch, have students fill in a T-chart that compares how the Grand Canyon and the cliffs at Big Sur formed. An example chart is shown below, with sample answers filled in.

Project Ideas To help your students apply their understanding of mechanical weathering, you may wish to have them complete some or all of the following projects. The time required to complete each project will vary; some may require students to work outside the classroom.
 * Students research a particular landform in their state that has been shaped by the forces of mechanical weathering. Have students identify the role that different agents of weathering might have played in its formation. Encourage them to describe how erosion, transportation, and deposition might have worked with mechanical weathering processes to shape the landform.
 * Students work in groups to create a model of wind erosion using materials such as a hair dryer, a shallow pan, and differently-sized sediments, such as sand and silt. Students should first write a description of the experimental setup they plan to use and a hypothesis on what they think will happen. After they perform the experiment, they should then write a brief conclusion explaining how the results compare to their hypothesis. If time allows, have students redesign their experimental setup and try again.
 * Students hypothesize how a local landform might change through time due to the effects of mechanical weathering. Have students write a short story from the perspective of a future scientist describing how the landform evolved over time. Encourage them to be creative, and include any impact on humans or the local ecology that might result from changes to the landscape.

Evaluate: Check for Understanding

Have students complete the Brief Constructed Response (BCR) item titled [|Mechanical Weathering]. You may also wish to assign the online concept assessment and use the results in the student reports to guide you in assigning any remediation to students.