1. What are the fluvial landforms produced by erosion? Learning Objectives: To understand how erosion makes fluvial landforms. 21 October 2013 Learning Outcomes: Essential – you will know the key words and terms. Stretch – you will explain the formation of each landform and explain why we find them at certain locations. Challenge – you will apply this understanding by labelling photos or diagrams and write top level exam answers.

2. Title: What landforms do we find down the long profile and how do they form? Lesson Objectives: 1.To investigate the development of landforms down the Long Profile 2.To answer a 15 mark past exam paper question on the development of meanders

3. Abrasion/ Corrasion Attrition Hydraulic Action The force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away. Rocks carried along by the river wear down the river bed and banks. Rocks being carried by the river smash together and break into smaller and smoother particles. Match the correct terms to the correct definitions

4. Abrasion/ Corrasion Attrition Hydraulic Action The force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away. Rocks carried along by the river wear down the river bed and banks. Rocks being carried by the river smash together and break into smaller and smoother particles. Match the correct terms to the correct definitions

5. May 2012 1 (a) Hydraulic action, abrasion and corrosion/solution are the relevant processes. There should be reference to how the processes work – hydraulic action is the removal of material by the sheer force of water. The turbulent flow of the water picks up loose material due to frictional drag. The higher the velocity – the more effective the process. Abrasion occurs when material being carried by the river hits the bed and banks and so wears them away via a scouring/sandpapering effect. The load used for this purpose will vary in size. Corrosion is the removal of certain rocks in solution – such as chalk and limestone where the mineral mixes with the rainwater and is carried away within it. Allow 1 mark for a list of two or more terms. 3 x 1 (3 marks) (3 marks)

6. Use your sheet to help you draw diagrams and add annotations to show how these landforms are created… Waterfalls, Meanders and Oxbow Lakes

7. Some landforms are the result of erosion, some are the result of deposition and some are the consequence of both! Waterfalls and Rapids -Sudden change in gradient of river -Usually due to changes in geology - resistant rocks lie on top of less resistant types - Waterfalls migrate UP the profile… HOW? Is a waterfall the result of Erosion, Deposition or both?

9. 1.Waterfalls Diagram

10. 1.Waterfalls Description of landform Erosional landform -1. hydraulic action in plunge pool -2. Headward erosion as waterfall retreats up river

11. 1.Waterfalls Process of Formation 1 – Water runs over more resistant rock and begins to erode a band of less resistant rock when it meets one. 2 – Hydraulic action and abrasion form a plunge pool at the bottom of fall. Starts to undercut the harder rock. 3 – Undercut rocks eventually fails to support weight of harder rock above and it collapses. Material falls into plunge pool causing abrasion. 4 – Over time as waterfall moves backwards a gorge can form.

12. 1.Waterfalls Distribution and Examples Falls normally occur in mountainous regions where there is a mixture of hard and soft rock British example: Highforce – Tees or Severn Breaks it’s Neck, R.Severn, Powys, Wales International example: Victoria falls, Zimbabwe (retreats 1m per year!!)

13. 1.Waterfalls Human Use/Adaption of Landform Tourist attraction Can sometimes be a source for electrical energy (Hydro Electric Power (HEP))

14. May 2011

15. 1 (a) (i) AO1 – 1, AO2 – 1, AO3 – 2 The obvious landforms are the waterfall, plunge pool and the associated gorge in the foreground. Allow 1 mark for each of these – maximum 2 for identification. The command word is ‘describe’ so there needs to be more than just recognition of the landforms for further marks. Labels may include reference to the two stages of the descent / the deeper part of the bed just after the descent / the presence of a plunge pool marked by the white water (if not awarded as an identification mark for recognising landform) / the channel occupying the width of the bed in the gorge or narrow channel / the stepped profile of the gorge or narrow channel / the eddying of the water in the gorge / or turbulent flow. Features must be correctly arrowed to be worthy of a mark – arrow must connect with landform / characteristic. 4x1 (4 marks)

16. May 2011 1 (a) (ii) AO1 – 5, AO2 – 2 The landforms to be explained are the waterfall and the gorge. There is likely to be reference to bands of hard and soft rock that are horizontally arranged, with the hard rock forming a cap rock, underlain by the soft rock. Differential erosion results and the softer rock is eroded faster than the hard rock, creating a steep gradient. There may be reference to specific processes of erosion, such as abrasion and hydraulic action. This causes the undercutting of the soft rock and an overhang develops above the plunge pool and its swirling waters. This ultimately collapses, causing the waterfall to retreat and to leave a narrow, steep- sided valley – the gorge – in its wake. This is the most likely explanation, but there may also be reference to rivers plunging over the edges of plateaus in southern Africa and South America and also to knick point waterfalls.

17. May 2011 Level 1 (Basic) 1-4 marks Begins to explain the formation of the waterfall/one landform. There is a partial sequence and general reference to process, such as erosion. Some use of appropriate terminology present at the higher end. L1 Begins to explain one landform L1 Partial sequence Level 2 (Clear) 5-7 marks Seeks to explain the sequence of the formation of the landforms – waterfall and gorge. There is some reference to both landforms, although one may be dealt with in greater detail. There will be greater reference to gorge through the level. Sequence is clear and there is reference to specific processes, such as abrasion. Appropriate geographical terminology is used. L2 Reference to both landforms. Clear sequence. (7 marks)

18. 2. Rapids Description of Landform Rapids increase the turbulence of a river and therefore it’s erosive power River Grading: Class 1 – Moving water with almost no gradient or obstacles Class 2 – Small regular waves Class 3 – Fall is slightly steeper and waves are slightly larger Class 4 – Rapids are more turbulent many rocks obstruct the rivers course Class 5 – Rapids are more severe and continuous. Very steep and rocky. Class 6 – Very violent, not used for human recreation, without extreme care

19. 2. Rapids Process of Formation Occurs when you find alternating bands of hard and soft rock Vertical erosion caused by the steepness of the localised gradient, means that the velocity of the river is faster and has more energy to erode. Soft rock erodes more quickly than hard rock causing rapids.

20. 2. Rapids Distribution and Examples Rapids are usually found in the upper course of a river often following on from waterfalls. Example of river with rapids: Colorado river, USA

21. 2. Rapids Human Use/ Adaptation of Landform White water rafting Kayaking (Grades 2, 3 and 4) Hydro-speeding Swimming (Grades 1 and 2)

22. 2. Rapids Diagram Localised gradient increase

23. 3. Potholes Description of Landform Potholes are erosional landforms. They are cylindrical holes ‘drilled’ into the bedrock by turbulence and high velocity flow. Adjacent potholes can join together to create sudden deepening of the river channel. Limestone is particularly susceptible to potholes.

24. 3. Potholes Process of Formation Abrasion occurs when the river picks up material and rubs it along the bed and the banks, wearing them away. The process is most effective during times of flood and is the major method by which the river is eroded vertically. If there are hollows in the river bed pebbles can become trapped and turbulent eddies in the current can swirl pebbles around to form potholes. Swirling of pebbles in holes is known as pothole ‘drilling’. http://library.thinkquest.org/28022/trail/potholes.gif

25. 3. Potholes Distribution and Examples Most occur along fast flowing rivers with strong eddying. Blyde River, South Africa

26. 3. Potholes Human Use and Adaption Can be tourist attraction as they sometimes look unusual.

27. 3. Potholes Diagram

28. Some landforms are the result of erosion, some are the result of deposition and some are the consequence of both! 4. Meanders Pools and Riffles -Rivers will always take the path of least resistance to the sea - Pool and riffle sequences formed during low-flow - hydraulic radius at low flow = stream competence, therefore deposition - deposition ‘s friction and therefore water prefers to flow around these areas creating pools Meanders -During high flow ( discharge) water ‘swinging’ around the riffle will be propelled towards the bank and undercutting erosion starts. - More deposition occurs near the riffle area creating a point bar on the inside of the bend. Is a meander the result of Erosion, Deposition or both? Helicoidal Flow -This allows eroded material from outer bank to be deposited in part on the inner bank of the next meander

29. 4. Meanders Description of Landform Meanders are bends and curves in the rivers course. Usually found in the middle course. River cliffs are found on the outer bends where there is more erosion Point bars (out of the water) and slip off slopes (under the water) are formed on the inside of the bend as there is slower flow and material is deposited.

30. 4. Meanders Process of Formation Pool and riffle sequences formed during low-flow Causes water to flow around riffles due to higher friction During high flow water ‘swinging’ around the riffle will be propelled towards the bank and undercutting erosion starts. More deposition occurs near the riffle area creating a point bar on the inside of the bend. Helicoidal flow (spiral flow) allows eroded material from outer bank to be deposited in part on the inner bank of the next meander increasing their size.

31. 4. Meanders Distribution and Examples The Mississippi has many meanders. Meandering causes the channel to move about forming meander scars and ox- bow lakes.

32. 4. Meanders Human Use Sometimes meanders can cause problems for navigating rivers. Channelisation is sometimes done to straighten the river eg The River Tees. The reclaimed land can be used for industry.

33. 4. Meanders Diagram

34. 5. Oxbow Lakes Description of Landforms Cut off from river channel Horseshoe shape They contain stagnant water which gets clogged up by plants and can dry up though infiltration and evaporation

35. 5. Oxbow Lakes Process of Formation Deposition occurs on the inside of a bend and erosion occurs on the outside due to the faster current Over time the loop of the meander widens until the neck joins The river takes the quickest course and so deposition occurs blocking off the meander so what is left is the horseshow shaped oxbow lake.

36. 5. Oxbow Lakes Distribution and Examples Lower course of river Found where there are large floodplains EXAMPLE:

37. 5. Oxbow Lakes Human Use Vary in size Can be used for fishing and sailing as they are still areas of water. On very large ones people can live on the well developed old point bars.

38. 5. Oxbow Lakes Diagram

39. Some landforms are the result of erosion, some are the result of deposition and some are the consequence of both! Is an ox-bow lake the result of Erosion, Deposition or both? 5.Oxbow lakes - Increasing sinuosity of the river - Deposition on the inner bank causes the ‘neck’ of the meander to become narrower - During times of high discharge the river cuts through the ‘neck’ creating a new channel

42. Jan 2011 (4 marks)

43. Jan 2011 Meanders are the most obvious feature – these are quite sinuous. There is evidence of the build-up of material on the inside bend (to right of photo) forming a gentle slip-off slope. There are levées present following the river’s course. The meanders are surrounded by an extensive flat gently sloping area – the flood plain. The meander belt extends across this. The valley sides (bluffs/river cliffs) rise beyond the extent of the meander belt. Allow 2 marks for identification. There must be reference to at least two landforms. 4x1. (4 marks)

44. How to answer a 15 mark Question… Describe and explain the development of meanders (15 marks) Unlike at GCSE your answer must be well structured. DON’T write a description and then an explanation. This must be incorporated. Make sure you are describing how meanders form in detail using key words eg don’t just say erosion occurs… what types?? Show that you understand what terms mean. Don’t just write ‘this is because of helicoidal flow’. Write ‘This is due to helicoidal flow which is… and therefore…’ Answer it in the correct order of processes eg start with pools and riffles and think about what happens next.

45. How to answer a 15 mark Question… Describe and explain the development of meanders (15 marks) Level 1 (1 to 6 marks): Language is basic, descriptions and explanations are over simplified and lack clarity. Defines/describes channel characteristics Describes changes of individual characteristics Level 2 (7 to12 marks) Generally accurate use of language; descriptions and explanations can be easily followed, but are not clearly expressed throughout. Clear description and explanation - some links Level 3: (13 to 15 marks) Accurate and appropriate use of language; descriptions and explanations are expressed with clarity throughout. Sequence, description and explanation are integrated - links clear, detailed.

46. Peer Assessment… Print p. 6 of mark scheme and give it to class to do some peer assessment (MUST BE IN PENCIL!!) don’t give out top bit (answer) 1.Take two coloured pencils and underline the bits you think they did really well in one colour and the bits you think they could improve in another. 2.Write 2 stars and 1 wish to help them understand your underlining. 3.Get your own work back and try to re-write the bits your peer marker thinks you can improve.