Upper Course Landforms
Introduction
This page looks at upper course river landforms, including potholes, waterfalls and rapids.
Enquiry Question
How do physical processes create distinct river landforms?
Lesson Time: 1 hour
Lesson Objectives:
- To describe and explain different river landforms, including potholes, rapids and waterfalls
Lesson - Upper Course Landforms
What do you already know?
- Starter Activity - Students are introduced to upper course landforms; remind them of the importance of erosion in the upper course. Then have them investigate the three sources, and they theorise how potholes form.
- Students can then read the text before writing a full explanation of their own. There is a good video on potholes too
- Processes - show the animation of the waterfall, and students should suggest what factors explain what is happening. They should pick out factors such as different geology, rock resistance, vertical erosion, a deepening plunge pool and the process of undercutting.
- Video - Place exemplification - Show the video on the River Tees, in England, and students should then complete the sequencing activity in the PDF worksheet provided. This is quite an easy first-step activity
- Differentiated written task - To add more challenge, students should write a full explanation of waterfall formation with lots of vocabulary. Get students to use as much of the wording in the box provided. A minimum of 8 words should be used. To write a fluid paragraph, students should use clear connectives so that the sentences and sequence flow.
Student Activity - Investigating River Processes in the formation of Potholes
Potholes are a bedrock feature that forms in the upper course.
Study the following sources and discuss what processes form potholes
Source 1
Source 2
Source 3
2. Read the following text, which explains the formation of potholes and write your own full explanation
Bedrock Landforms
Many upper-course landforms in high mountains form on bedrock. Rivers vertically erode into the bedrock, so it's useful to consider upper-course landforms as bedrock landforms. Examples include potholes, rapids and waterfalls. All of which result from vertical erosion due to the high potential energy that comes from gravity. This is then converted into kinetic energy as the river attempts to cut down to its base level.
Student Notes:
Potholes form mainly in the upper course of the river, at high altitude where the river channel cuts directly into the bedrock. Potholes are the direct consequence of vertical erosion and processes of abrasion. The sequence of development is quite easy to understand. As we know, the river channel in the upper course is characterised by roughness, associated with a large bed load. As water flows over bed load, the force of the water eddies into the rock downstream. Over time, small depressions within the bedrock develop. We can see a similar process of turbulent wind movement and eddy development as wind collides with tall buildings in cities. This is illustrated below:
Student Activity - Processes - Rapids and Waterfalls
Most rapids and waterfalls form in areas of geology where differences in resistance occur, leading to differentiated rates of erosion. This leads to steep steps or a series of steps in the river, where several important features are found.
Watch the following animation of a waterfall and suggest reasons for what is happening.
Student Activity - Place and Processes - High Force Waterfall, River Tees
Watch the clip of the waterfall and annotate the photograph of High Force with its specific features.
Then complete the sequencing activity below
Sequencing ActivityStudent Notes:
Rapids are most commonly found in the upper course of the river and form as a result of the river cutting down rapidly in a localised section of the river. They may form downstream of a waterfall that has retreated. They can be found in other sections of rejuvenating rivers and are located at the knick point of the river. The main characteristics of rapids are distinctly steeper gradients marked by steps in the channel and high turbulence, which is the result of a large bed load in the channel or steps. Commonly, rapids form over different bands of geology that vary in resistance or where the river is transporting a large resistant bed load. The velocity of the river is noticeably faster at rapids but not efficient in its flow. Due to the roughness of the channel, flow is turbulent and known as white water. This white water is thrown up and characterised by eddy currents. The following photograph shows the dry river bed under the potential rapids.
Waterfalls like rapids form mainly in the upper course as a result of differentiated erosion. If the river channel flows across different bands of geology with varying resistance, then the softer, less resistant rock will be eroded faster, creating a step in the river. The hydraulic action of the water enlarges this step over time, creating the waterfall. Due to the force of the water, a deep plunge pool forms at the base of the waterfall. Turbulent flow with eddy currents and splashback undercuts the cap of resistant rock headward until the undercut is significant enough for the rock above to collapse under its weight. This leaves angular, resistant bedload in the plunge pool, which will combine with hydraulic action to further deepen and undercut through the process of abrasion. Over time, the waterfall becomes higher and retreats upstream. As the waterfall retreats, a deep gorge with steep sides forms down the length of the river and marks the length of retreat. Waterfalls are a significant example of both vertical and headward erosion.
Complete the following essay using student access
Explain the processes that form different landscape and river features in the upper course of a river (10 marks)
Tip: Write a an introduction - this should act as summary of the key processes and landforms you will refer to in the essay
Develop at least three different landforms in the main body
Conclude your essay