waterfall

Question 1

What type of rock does water flow over in a waterfall?

Answer 1

Alternating bands of harder rock, eg limestone and softer rock eg clay

Question 2

What does differential erosion do?

Answer 2

Overtime, differential erosion causes the softer rock to be eroded at a much faster rate than the hard rock

Question 3

How does the river erode the rock? (Processes)

Answer 3

The river erodes the rock in three main ways:
-hydraulic action- when the sheer force of the water crashing into the rock erodes it. Water gets into small cracks in the rock and breaks it down, or air is compressed into the cracks, causing matieral to be dislodged

• corrasion- when the river throws its own bedload (pebbles, rocks) against the rock causing erosion
• corrosion- the chemical erosion of the rock by acids in the water, which weaken the rock and eventually wear it away

Question 4

Because of differential erosion, the river undercuts the harder rock: What does this cause?

Answer 4

An overhang of harder rock

Question 5

What happens to the over hang over time?

Answer 5

It becomes unsupported, and collapses due to gravity, falling into the plunge pool below it
This asists in the process of attrition which happens in the plunge pool- where rocks hit and scrape off of eachother, and become smoother, smaller and rounded, as well as further corrasion.

Question 6

What deepens the plunge pool?

Answer 6

The further corrasion from the fallen overhang and the rocks already in the plunge pool
The plunge pool is also deepened at times of high discharge, this is because this is when hydraulic action is at its strongest

Question 7

As the process continues, the waterfall retreats upstream: what else happens?

Answer 7

A steep sided gorge is cut back into the hillside

Question 8

What is an example of a waterfall?

Answer 8

Angel falls, Venezuela

Question 9

EXPLAIN FULLY How a waterfall is formed

Answer 9

A river flows over alternating bands of harder rock eg limestone and softer rock, eg clay.
Overtime due to the process of differential erosion, the softer rock (being less resistant to erosion) is eroded away at a much quicker rate than the harder rock which is more resistant to erosion.

The river erodes the rock in three main ways:
-hydraulic action- erosion by the sheer force of the water; water gets into small cracks in the rock and breaks the rock down and/or hydraulic action can compress air into the cracks which causes material to be dislodged
-corrasion- when the river throws its own bedload (pebbles, rocks) against the rock, causing erosion
-corrosion- the chemical erosion of the rock by acids in the water, which weaken the rock ans eventually wear it away
The river undercuts the harder rock, and this causes an over hang of rock. Overtime, the overhang becomes unsupported and collapses due to gravity into the plunge pool below it. This assists in the process of attrition which occurs in the plunge pool; when the rocks hit and scrape off of eachother, so they become smaller, smoother and rounder. This also assists in further corrasion, which deepens the plunge pool.
The plunge pool is also deepened at times of high discharge, because this is when hydraulic action is at its strongest.
The process continues and the waterfall retreats upstream, and a steep sided gorge is cut back into the hillside.