Waterfalls occur when rivers flow over areas with different rock types. Softer rock erodes faster than harder rock, creating a step over which water plunges as a waterfall. As erosion continues, water cuts away rock behind the waterfall, causing it to move back upstream and leave a gorge. Over time, this process eats away at the soft rock, undercutting the hard rock above and causing sections to collapse, further deepening the plunge pool.

1. Waterfalls

2. Objectives
To be able to:
Define waterfall
Explain, using specific terms,
how they are formed
Explain, using specific terms,
how they are worn away
Make clear links to your
previous work on rivers

3. What is a waterfall?
• Definition?

4. What is a waterfall?
• Definition
A waterfall is a
geological formation
where flowing water
rapidly drops in
elevation as it flows
over a steep region
or a cliff.

5. How are waterfalls formed?
Waterfalls occur when ______ flow over different
types of ____. The ____ rock wears away faster
than the ____ rock. In time a step develops over
which the river _______ as a waterfall. _____also
cuts away rock behind the _________. This
causes the falls to move back and leave a _____
as it goes.
HARD RIVERS WATERFALL ROCK
SOFT WATER PLUNGES GORGE

6. How are waterfalls formed?
Copy out the paragraph below and insert the missing words from the word bank.
Waterfalls occur when RIVERS flow over
different types of ROCK. The SOFT rock wears
away faster than the HARD rock. In time a step
develops over which the river PLUNGES as a
waterfall. WATER also cuts away rock behind
the WATERFALL. This causes the falls to move
back and leave a GORGE as it goes.

7. How are waterfalls formed?
The hard rock
collapses into the
plunge pool to be
broken up and
washed away by
the river. The
position of the
falls moves back.
Falling water and
rock particles or
boulders loosen
and wear away the
softer rock.
Erosion continues
and the waterfall
slowly eats its way
upstream leaving a
gorge behind.
The hard rock
above is
undercut as
erosion of the
soft rock
continues.
The diagrams below have been given the wrong labels. Can you figure out
which description matches each diagram?

8. How are waterfalls formed?
The hard rock
collapses into the
plunge pool to be
broken up and
washed away by
the river. The
position of the
falls moves back.
Falling water and
rock particles or
boulders loosen
and wear away the
softer rock.
Erosion continues
and the waterfall
slowly eats its way
upstream leaving a
gorge behind.
The hard rock
above is
undercut as
erosion of the
soft rock
continues.

9. How is a waterfall worn away?
In your exercise books, stick in the
circular flow diagram.
Put the labels below on the cycle in
the right order.
• Hard rock collapses
• Soft rock worn away
• Waterfall moves back
• Plunge pool deepens
• Hard rock undercut
?
?
??
?

10. How is a waterfall worn away?
Soft rock
is worn
away
Hard
rock is
undercut
Plunge
pool
deepens
Hard
rock
collapses
Waterfall
moves
back

11. Waterfall labelling

12. Waterfall diagram
• Use the word bank to label the photograph.
A = WATERFALL
B = PLUNGE POOL
C = RIVER
D = SOFT ROCK UNDERCUT
E = HARD ROCK OVERHANGS
F = GORGE

13. Waterfalls of the World; Fact File
• Angel Falls, Venezuela (979m high, 47 drops)
• Niagara Falls, Canada & USA (52m high, 1
drop)
• Iguazu Falls, Argentina (82m high, 275 drops)
• Victoria Falls, Zimbabwe (108m, 1 drop)