Key terms

1. Key terms

2. Let’s see what we have managed to cover this half term. CHECKLISTS

3. Learning objectives To understand landforms of fluvial erosion and deposition. • Potholes • Rapids • Waterfalls • Gorges • Meanders • Oxbow lakes • Braiding • Floodplains • Levees • Deltas Upper course landforms Lower course landforms

4. Overview

5. Landforms Overview • Rivers are constantly shaping the landscape as they carry water and sediment along their courses • Where a river has excess energy it will erode its channel creating waterfalls and gorges. • When energy levels fall deposition will occur forming extensive floodplains • Erosion and deposition can combine to form meanders

6. Can you match up the landforms and the pictures?

8. 1. Potholes • Potholes are circular depressions in the river bed • Process • Rock fragments are drilled into holes/cavities by the turbulent whisking action of a river • Erosional process = corrasion • Rock will overtime become smooth = Abrasion

10. Kukdi River, Nighoj, India Pothole and the rock fragment that formed it

12. ACTIVITY - Draw two diagrams to show the processes that cause a pothole to form Over time, they may widen and join with other potholes to form larger potholes, and the whole river bed is deepened.

13. 2. Rapids • A river flows over a variety of different rock • Tougher rock = eroded less easily • Weaker rock = eroded quicker • This results in irregular steps in the long profile of a river • Cause turbulent flow in a stretch of river • This is known as a rapid.

14. Rapids form stretches of white water as the river plunges over jagged rocks and mini waterfalls to form dangerous whirlpools and fast-flowing tubes of water

16. How do you think waterfalls are formed?

17. Who can name and describe the formation of these landforms?

18. Learning objectives To understand landforms of fluvial erosion and deposition. • Potholes • Rapids • Waterfalls • Gorges • Meanders • Oxbow lakes • Braiding • Floodplains • Levees • Deltas Upper course landforms Lower course landforms

19. High Force – River Tee 3. Waterfalls

20. Watch this! • http://www.youtube.com/watch?v=jqCR-9nBgWQ • http://www.youtube.com/watch?v=YP1J1csZaCM&feature=related

21. EXAMPLE High Force waterfall on the River Tees • Water plunges 20 metres over the edge of a tough outcrop of dark igneous rock called dolerite • Beneath the dolerite are mainly sedimentary rocks like limestone and shale • Sedimentary rocks erode quicker causing the formation of a plunge pool • This undercuts the waterfall at its base causing the overhanging dolerite to collapse • This cycle repeats • Formation of a 1.5km gorge. http://maps.google.co.uk/maps?hl=en&q=river%20tees%20map&bav=on.2,or.r_gc.r_pw.r_qf.&bpcl=37189454&biw=1024&bih=648&wrapid=tlif135218804049521&ie=UTF-8&sa=N&tab=il

22. Waterfall Formation

23. Waterfall Formation

24. ACTIVITY 2 Create a story board to the formation of HIGH FORCE waterfall in the upper course of the River Tees. • Use the 6 statements to help you do this. • Label your diagrams with these key words 20 metres COLLASPE PLUNGE POOL OVERHANGING DOLERITE LIMESTONE AND SHALE HYDRAULIC ACTION RETREAT CORRASION 1.5 km GORGE UNDERCUTTING

25. The formation of a waterfall – Example___________________________

26. The water starts to undercut soft rock underneath the hard rock, creating the beginnings of a plunge pool • Water flows over a gap in hard rock • Falling rock and the force of water also help to create a plunge pool through erosional processes like hydraulic action and corrasion • As the waterfall retreats it leaves a steep-sided gorge. Over thousands of years the waterfall can move several miles • The waterfall retreats over time, with the process starting again • The overhanging hard rock eventually falls into the water as the base of the waterfall has been undercut

27. Water flows over a gap in hard rock • The water starts to undercut soft rock underneath the hard rock, creating the beginnings of a plunge pool • The overhanging hard rock eventually falls into the water as the base of the waterfall has been undercut • Falling rock and the force of water also help to create a plunge pool through erosional processes like hydraulic action and corrasion • The waterfall retreats over time, with the process starting again • As the waterfall retreats it leaves a steep-sided gorge. Over thousands of years the waterfall can move several miles

28. Learning objectives To understand landforms of fluvial erosion and deposition. • Potholes • Rapids • Waterfalls • Gorges • Meanders • Oxbow lakes • Braiding • Floodplains • Levees • Deltas Upper course landforms Lower course landforms

29. The Middle Course of the River

30. Learning objectives To understand landforms of fluvial erosion and deposition. • Potholes • Rapids • Waterfalls • Gorges • Meanders • Oxbow lakes • Braiding • Floodplains • Levees • Deltas Upper course landforms Lower course landforms

31. The Middle Course • More tributaries join the River Severn. • These increase the volume of water in the River. Increasing the River’s Discharge. Middle course Upper Course

32. LANDFORM of the Middle/Lower CoursesFlood Plains • During wet weather rivers increase in size. • Sometimes rivers cannot hold all of the water flowing into them. • The banks burst and the river floods on a flood plain. • Therefore a flood plain is the area of broad flat land either side of the river.

33. The floodplain creates U shaped valleys in the middle course. FLOODPLAIN

35. 5. Meanders Meanders are sweeping bends in the river’s course MEANDERS ARE FORMED DUE TO EROSION AND DEPOSITION!! What is a meander?

36. Watch this!!!

37. Processes that cause a meander to form…. Pool and Riffles are created due to the ‘corkscrew’ (helicoidal) like flow. Pools and riffles often occur in meandering channels during low flow conditions Riffles – shallow, fast flowing water Pools – deep, slow flowing water • When a river emerges from the upper course, it begins to ‘swing’ or meander in order to use up surplus energy • This is because water moves in a helicoidal flow! SWIRLS!

38. Processes AND features of a meander Water flows faster on the outside bend, due to centrifugal force. This fast flowing water is called the THALWEG. This causes LATERAL EROSION through ABRASION. This creates a RIVER CLIFF. A B Draw a plan view of a meander • Water flows much slower on the inside bend as the river lacks energy to carry its load. This causes DEPOSITION. This creates a slip off slope.

39. Can you label the correct processes and landforms of a meander? What is a cross section?

40. Cross Section From A to B Information on the outside of the meander… B - inside A - outside Outside-The volume and velocity of the river are higher UNDERCUT Material is carried inSUSPENSION The force of the water ERODES and UNDERCUTS the river bank by ABRASION The water has more energy to transport its load Fastest flowing water is called the THALWEG This feature is called a River Cliff

41. Cross Section From A to B On the inside of a meander…. A - outside B - inside The river is shallow and slow flowing Material is thereforedeposited The river lacks the energy to carry its load This feature is called a POINT BAR

42. Processes creating meanders… DEPOSITION On the inside of a bend LATERAL EROSION On the outside of a bend

43. 6. Oxbow Lakes

44. Lateral erosion on outer bend Continued erosion results in the narrowing of the neck of the meander The two outer bends meet .The river takes the shortest route. Deposition occurs in slack water. The river cuts the most efficient course. It cuts off the former bend, leaving an oxbow lake

45. PREP • Create a A3 summary sheet of landforms of rivers as they move downstream • UPPER, MIDDLE AND LOWER COURSE • Use as many key words around the diagrams as possible!

46. 6. Formation of a Oxbow Lake

47. Cross Section of a meander From A to B

49. The Lower Course landforms

50. Learning objectives To understand landforms of fluvial erosion and deposition. • Potholes • Rapids • Waterfalls • Gorges • Meanders • Oxbow lakes • Braiding • Floodplains • Levees • Deltas Upper course landforms Lower course landforms