Upper Course Landforms

Question 1

Waterfalls

Answer 1

Form where hard rock lies upon soft rock. Th discordant layers lead to differential erosion.
- Vertical erosion creates plunge pool due to the gravitational pull of water down a sudden change in gradient and soft rock is undercut by erosion(HA and A).
- Plunge pool gets bigger and hard rock above left without support. Continual undercutting increases the gravitational pull of the overhang until it eventually collapses.
Fallen rocks transported away. Waterfall retreats and moves upstream creating a gorge.

Question 2

Potholes

Answer 2

Boulders broken off by erosion sit in natural dip in the river bed
Eddy current swirls the boulders as the river currents flow past (as the currents aren’t strong enough to move boulders via traction)
The swirling movement of boulders by the eddy current erodes the bed creating a pothole by abrasion as the boulder grinds a hollow in the river bed due to vertical abrasion.

Question 3

Braided Channels

Answer 3

Occur where highly variable discharge; large amount of sediment and easy eroded banks e.g glacial streams

• Low discharge, more friction, low velocity, low energy, low competence, leads to deposition of sediment. Water forced to flow around these islands of deposition to form braided channels. The banks formed are generally unstable and easily eroded
• Increase in discharge, less friction as deeper, high velocity, more energy, more competence. River can erode braided channels and transport the sediment
• Discharge falls, more friction as shallow so low velocity, low energy and competence so material is re-deposited to form new islands
• Sand bars and channels constantly change

Question 4

Rapids

Answer 4

River flows over bands of hard and soft rock, where gradient suddenly changes.
Hard rock erodes slower and less easily
Soft rock erodes faster and easier
Steepens river gradient and increases water velocity as it rushes down the rocks. This produces white water as it speeds down the steeper section.

Question 5

V shaped Valleys

Answer 5

Low discharge means only downward erosion can occur due to limited energy. Vertical erosion is in the form of HA and A.
Weathering weakens valley sides e.g chemical, frost and biological.
Continued vertical erosion at base of valley
Mass movement of material occurs down valley sides due to gravity
Creates V shaped valley
Material transported away in suspension traction etc when enough energy.