Year 7 Geography- Rivers (B and P groups)
Lesson 4 – Explain how erosion creates a waterfall and a gorge
Success criteria: I can name two landforms caused by river processes I can explain how a waterfall is formed I can explain how a waterfall becomes a gorge I can explain what attrition is
Do now:
1. When water is evaporated from plants it is called…
2. Erosion is…
3. What is the type of erosion where water forces material from the river banks?
4. Abrasion is…
5. Name two LICs…
6. Corrosion is…
Three processes occur within a river- erosion, transportation and deposition. These processes create a number of different landforms. This lesson focuses on the creation of waterfalls and gorges. Waterfalls:
A waterfall is a steep fall of water, where water flows over a ledge of hard rock.
Waterfalls happen in areas where hard rock overlies soft rock.
The soft rock erodes more quickly than the hard rock, creating a plunge pool and overhanging ledge.
.
Further erosion of the soft rock, makes the plunge pool deeper and the overhanging ledge unstable. Eventually the ledge falls into the plunge pool.
As the steps 1-3 are repeated, the waterfall retreats upstream.
Using the information above, explain each stage of waterfall formation.
• Label the diagrams with these key words: soft rock, hard rock, plunge pool, overhanging ledge, abrasion, hydraulic action.
Waterfalls happen in areas where ______overlies ______.
The ______erodes more quickly than the ______, creating a p______p______and o______l______.
Further erosion of the soft rock, makes the plunge pool ______and the overhanging ledge unstable. Eventually ______.
Gorge:
A gorge is a narrow, steep sided valley that is found further down a river from a waterfall. A gorge is formed as a waterfall moves backwards because of erosion.
Exit ticket
True or false?
1. A waterfall comes before a waterfall in a river. TRUE / FALSE 2. Soft rock overlies hard rock. TRUE / FALSE 3. Waterfalls and gorges are landforms found in rivers and formed by erosion TRUE / FALSE 4. A gorge is a valley with gentle sloping sides TRUE / FALSE
Challenge: how do you think waterfalls and gorges will change over time?? ______