Lesson 6: Formation of a

Waterfall

What you should know by the end of this lesson:

Explain the formation of a Waterfall

Background

A typical river formation question would be:

Explain the formation of a *.

You may wish to use an annotated diagram in your answer (8)

*The features you can be asked are:

- Waterfalls
- V-shaped valleys
- Meanders
- Ox-Bow Lake

V-Shaped Valleys & Waterfalls usually form in the upper course of rivers, where the land has a very steep gradient.

They are the result of both river erosion and weathering (breaking down of rocks by the weather). Waterfalls come in a wide variety and there are a few variations in their formation, but for River waterfalls, this is how they form.

Digital Workbook and Paper Jotter

Draw the annotated diagram for the feature
Write out the explanation under each

Reminder

Fully explained processes will gain you double marks. 1 mark for naming the process and 1 for explaining the term but you NEED to do both to get both marks.

Formation of a waterfall and gorge.mp4

River Landforms: Waterfalls

1. In the upper course of the river, where there is a band of hard rock overlaying bands of soft rock (1) differential erosion takes place (1) through

2. Hydraulic action (1), when air is compressed into the river bank dislodging material (1) and

3. Abrasion (1), when the force of the water throws the material against the banks (1).

4. The softer rock is more easily eroded (1)

5. This erodes underneath the hard rock, causing an overhang (1)

6. Over time the overhang is unsupported (1) and will collapse into the plunge pool due to gravity (1)

7. Attrition occurs here breaking the rocks down (1)

8. The waterfall will then retreat upstream creating a gorge (1)

Extra: Gorges

The process of undercutting, overhanging and collapse continue over thousands of years.

This moves the waterfall upstream, leaving a steep-sided gorge.