formations (waterfall, gorge, meander, interlocking spurs, potholes, oxbow lake)

Question 1

formation of a waterfall

Answer 1

• when a river flows over a layer of hard rock followed by a layer of softer rock
• softer rock is eroded quicker causing a knick/step in the river bed
• the force of the water undercuts the harder rock and creates a plungepool at the riverbed
• the hard rock is left overhanging and because it isn’t support it eventually collapses
• the hard rock falls into the plunge pool and they swirl around causing more erosion through ATTRITION
• overtime, the process repeats and the waterfall continuously moves upstream, leaving behind a gorge

Question 2

formation of gorge

Answer 2

• formed when the waterfall retreats overtime upwards
• the flow of water over a layer of harder rock followed by layer of small rock
• the small rock erodes faster by hydraulic action and abrasion, creating a undercut beneath harder rock
• hard rock is left overhanging and eventually collapse into plungepool as it doesn’t have any support
• the process repeats and the waterfall continuously retreats upstream
• as waterfall retreats, it leaves behind a steep sided valley called agorge

Question 3

formation of meander

Answer 3

• as a river goes around a bend, most of the water is pushed to the outer bend
• the line off fast flowing water is called the Thalweg
• fast flowing water causes increased speed therefore increased erosion
  (through hydraulic action and abrasion)
• the lateral erosion on the outside bend causes undercutting of the river bank forming a river cliff
• water on the inner bend travels slower, causes water to slow down, lose energy and deposit the eroded materials, creating a gentle slope of sand and shingle called a POINTBAR.

Question 4

formation of pothole

Answer 4

• boulders broken off by erosion that sit on the riverbed
• create swirling eddy currents as water flows past
• as river is not yet strong enough to move the boulders by traction
• eddies: swirl the boulder round and erode a pothole in the riverbed by vertical erosion
• pebbles get trapped in it and the flow causes them to erode further, creating a smoother base

Question 5

erosion in action

Answer 5

• on the outside bend, the water is travelling fast and the river is eroding the riverbanks
• the material being transported in their river is scraping against the side of the riverbanks,
  wearing it away called abrasion
• also the fast water is smashing against the river banks and getting into the cracks, causing the rocks to break apart and weaken in the process called hydraulic action
• underneath the water, the pebbles knock against each other, causing them to break apart and become more rounded called attrition

Question 6

deposition in action

Answer 6

• on the inside bend, the water is travelling more slowly
• it no longer has the energy to carry materials in suspension so the material is deposited

Question 7

formation of oxbow lake

Answer 7

1. obstruction, disturbance in flow of the river
   - water starts moving in a different direction
   - starts erosion on the riverbank
2. inside bend - deposition occur - due to loss of energy
   - load amount - friction - causes slow flow of water
   - causing material to deposit
3. overtime meander gets bigger
   - at the NECK of meander, two outside bend get closer
   - if flooding occurs - neck is cut off and the river flows straight
   - deposition occurs at the end of the curve, - oxbow lake is formed