Activity 2: Valleys
Erosion creates three different types of river valleys, all of which are distinct and beautiful. These three different types of valley, their shapes and how they are formed will be discussed in this activity.
Instructional Method: Demonstration
Goal: To demonstrate how different valleys are formed by flowing water or ice.
Objectives: Students will be able to:
Preparation: 30 min.
There are three main types of valleys:
Each type of valley is formed by erosion. Valleys are landforms with two valley walls and a bottom of varying width. Many have river channels along the valley floor. V-shaped valleys and river plain valleys are formed by flowing water. U-shaped valleys are formed by flowing ice, or glaciers.
V-shaped valleys have steep valley walls with narrow valley floors. In cross section it has a "V" shape. They are created by fast flowing rivers with steep gradients. As rivers flow downhill quickly, they remove more sediment from the bottom of the stream channel than from the sides. This process is called down cutting. It can be compared to a knife cutting through a cake. The resulting landform is a narrow canyon with a fast flowing river and little bank, or floodplain, on the river sides. An example of such a valley is found in Grand Canyon National Park and Black Canyon of the Gunnison National Park . For more information about stream channels and erosion go to Changing Landforms in Mid-stream.
River plain valleys have broad flat valley floors with sides of varying angles. The valley bottom is formed by a meandering river. Plain valleys are created by slow moving rivers flowing at moderate to low angle slopes. A river at this gradient tends to erode more along the sides of the channel than along the bottom. Thus, the river slowly sweeps across the valley floor, forming a broad river plain.
U-shaped valleys are formed by slow flowing ice called glaciers. Glacially carved valleys have the name U-shaped because in cross section they resemble the letter 'U'. They have a curved floor with steep sides. Floor gradient does not affect the valley's shape, it is the glacier's size that does. Continuously flowing glaciers and large sized glaciers carve wide, deep incised valleys.
Glaciers flow downhill slowly, over long periods of time due to gravity. As glaciers flow they pick up rock from the valley floor and carry it along. Glacier transported sediment scrapes against the valley floor, digging deeper and carrying more sediment, carving out the shape of the valley. There are two types of glaciers: alpine glaciers (that form U valleys) found in mountainous regions, and continental glaciers (that destroy topography) which are huge ice sheets covering large portions of continents.
More information about glaciers can be found by checking out the links below. The following three activities allow students to create the valleys discussed.
1. V-shaped valley
2. River plain valley
3. U-shaped valley
After students create the landforms, have them draw a sketch of what was formed. On the sketch, label the direction the water or ice was flowing. Label which erosional process created the landform. Why do some rivers create V-shaped valleys and some create plain valleys? Are there any river valleys in your area? If so, what kind of valleys do you find? Are there any glacial valleys in your area? If so, do you know when the glaciers that created them were there?
Instead of using water, use your hand as the river cutting through the sand. It works great and is less messy. Make sure you do not wiggle your hand for the V-shaped valley. For the meandering streams make sure you wiggle your hand back and forth, acting like a meandering stream. For the U-shaped valley you can substitute your fist.
Ask students to perform the same experiments with different hill slope angles, with different rates of water flow (slow or fast). What landforms resulted from the variations?
Included National Parks and other sites:
Black Canyon of the Gunnison National Park
Utah Science Core:
4th Grade Standard 5 Objective 1,2