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Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 2.3 How does a river shape the land along its different courses?

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Presentation on theme: "Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 2.3 How does a river shape the land along its different courses?"— Presentation transcript:

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2 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 2.3 How does a river shape the land along its different courses?

3 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes How do the characteristics of a river change along its course? Can you find these kinds of landform at the same place?

4 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What are the different sections along a river course? Upper course Middle course Lower course They are different in _________ and _____ _______. gradient river energy Relatively straight, with bends around obstacles Winding Big bends occur

5 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What are the different sections along a river course? Gradient of the upper course: ______ Gradient of the middle course: __________ Gradient of the lower course: _______ steep moderate gentle

6 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes The energy and work vary along the three courses, different landforms are formed! What are the different sections along a river course? Therefore, different landforms are found at different sections along a river course. Upper course Middle course Lower course

7 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What landforms are formed at the upper course? Is this the impression you have for the upper course? What do you think about the energy of river at the upper course when compared with the middle and lower course? (Greater / Less) The catchment areas of the tributaries at the upper course is (large / small). The amount of the channel water is (large / small). The energy is less because: Large boulders in the channel (increase / decrease) the channel roughness. (Much / Less) of the energy are used for overcoming friction. How much energy is there?

8 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What landforms are formed at the upper course? What is the work involved? The cross-section of a valley at the upper course ________ erosion is the dominant work at the upper course. Vertical Headward erosion also occurs when water starts to gather. Because of the small river energy, the rate of erosion is (slow / fast). (Small / Large) load can be transported. Deposition is (common / rare). What is the direction of the erosion at the upper course?

9 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What landforms are formed at the upper course? What are the landforms produced? Landforms at the upper course Interlocking spurs RapidsPotholes GorgesWaterfalls

10 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes How is the land shaped at the middle course? How much energy is there? How much energy is there at the middle course when compared with the upper course? (Greater / Less). Do you know why? More tributaries are joining the river. The amount of river water (increases / decreases). The river energy (increases/ decreases). The channel becomes _________. The water flows ______. smoother faster

11 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What is the work involved? How is the land shaped at the middle course? What is the main work at the middle course? (Erosion / Transportation / Deposition) Why? The river flow is faster and with more energy. Erosion occurs, but there is extra energy for _____________. transportation

12 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What are the landforms produced? How is the land shaped at the middle course? Landforms at the middle course Slip-off slopesRiver cliffsMeandersBluffs

13 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What landforms are formed at the lower course? How much energy is there? Is the energy large or small at the lower course?

14 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What landforms are formed at the lower course? How much energy is there? The cross-section of s valley at the lower course The channel here accommodates (less / more) water than that of the upper course. The river bed is (smooth / rugged), so the friction here is greatly (reduced / risen). It has the (smallest / largest) discharge among the three courses. Therefore, the flows are at a (low / high) speed. The lower course has the (highest / lowest) energy.

15 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What landforms are formed at the lower course? How much energy is there? Does it mean the river energy is high all the time at the lower course? (Yes / No) The river energy drops when: the channel flow is blocked by sea water at the _______ of the river. mouth the amount of river water is reduced during the (wet / dry) seasons. flooding occurs and the flood water has not yet retreated from the valley floor.

16 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What landforms are formed at the lower course? What is the work involved? Erosion- at the (inner / outer) banks of the river. Transportation- bringing the load towards the mouth of the river. Deposition- whenever and wherever speed of flow is lowered. What is the work at the lower course? (Erosion / Transportation / Deposition) Ha! Ha! All three work occur at the lower course!

17 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What landforms are formed at the lower course? What are the landforms produced? Landforms at the lower course Flood plains Deferred tributaries Oxbow lakes Deltas Levees Braided streams

18 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes Case study: How does the Chang Jiang change along different courses? Upper course Middle course Lower course Yichang Hukou Tuotuo He

19 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes Case study: How does the Chang Jiang change along different courses? Do you know any characteristics of the Chang Jiang? The longest river in China and ______ longest in the world. Average annual discharge: 30,000 m 3 /sec. The load is not heavy as compared with the __________. It flows past the ___________ _______ humid area of China. About % of the river water comes from _______. rainfall third Huang He humid subtropical

20 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes Case study: How does the Chang Jiang change along different courses? Middle course Lower course Upper course

21 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What are the characteristics of the upper course of the Chang Jiang? The river source: The Tuotuo He At the Jinsha Jiang The discharge is small. The gradient is gentle. The river flows slowly. South-flowing. The channel winds through interlocking spurs. The gradient is steep. The Hutiaoxia at the Jinsha Jiang Vertical erosion

22 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What are the characteristics of the upper course of the Chang Jiang? At the Sichuan Pendi More rainfall Many large tributaries join the main channel Discharge increases rapidly Great erosive power Forms Sanxia

23 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What are the characteristics of the middle course of the Chang Jiang? A big drop in _______ and the _________. altitude gradient Meanders are formed. Numerous lakes are found, e.g. Dongting Hu. 286 km Length of the river between them: 712 km

24 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes What are the characteristics of the lower course of the Chang Jiang? The land is flat and low, e.g. the Chang Jiang Delta plain. The tributaries are shorter than those in the middle and upper courses. Many meanders and braided streams. Levees and deferred tributaries are found. Delta and lagoon are formed, e.g. Tai Hu.

25 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes How does a river basin work as a system? What is a system? It is a group of things that interact within a boundary to perform some functions. It includes _______, __________ and ________. inputsprocessesoutputs Open systemClosed system Energy Matter Input Processes Output Boundary of the system Energy Matter

26 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes How does a river basin work as a system? Inputs ProcessesOutputs Solar radiation Water Rocks Radiation Conduction Evaporation Absorption Precipitation Exogenetic processes Channel outflow Evapo- transpiration Transportation Heat Water Vapour Sediment Weathering Mass movement Erosion Interception Drip flow/ Stem flow Surface run-off Infiltration Subsurface run-off Transportation Deposition

27 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes

28 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes ________ erosion deepens the channel and makes the obstacles more marked. 1Interlocking spurs What are the landforms produced at the upper course? They are the spurs interlocking with each other. Vertical The river has too little energy to remove obstacles, so the river water flows around them. Interlocking spurs Valley is deepened

29 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 2Gorges What are the landforms produced at the upper course? Downcutting is (slower / faster) than lateral erosion. This creates a (deep / shallow) and (narrow / wide) V-shaped valley, i.e. gorges.

30 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 3Rapids What are the landforms produced at the upper course? The river water is unable to erode the layer of _________ rock. resistant The river bed becomes (even / uneven). The turbulent currents are called rapids. Rapids

31 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 4Waterfalls What are the landforms produced at the upper course? Less resistant rock is eroded by river water at a (slower / faster) rate. The river falls vertically down. The falling water produces strong _________ action, forming a circular hollow filled with water. hydraulic Water flow Waterfall forms Large angular boulders Plunge pool forms

32 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 5Potholes What are the landforms produced at the upper course? When a river flows over an uneven surface, it causes ___________ in the water. turbulence What is this? A pothole is formed when the water drills with the load it carries. How does it form? Pothole Which type of fluvial erosion is involved within the potholes? Abrasion.

33 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 1Slip-off slopes and river cliffs What are the landforms produced at the middle course? Which part of the river has the fastest flow? Fastest part of the river flow What are the work involved at the inner and outer bank? Outer bank: ______________ Inner bank: __________ lateral erosion deposition What are the two landforms produced? River cliff Slip-off slope River cliff Slip-off slope

34 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 2Meanders What are the landforms produced at the middle course? The outer bank gets worn away through _______. erosion The inner bank builds up through __________. deposition The river (bends/ straightens). Each bend is called a meander. Outer bank Inner bank Meander appears Lateral erosion creates river cliffs More concave More convex Slip-off slopes form Faster stream of water thrown towards outer banks Sediment Low river cliff

35 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes __________ at outer bank are pushed back and join into lines, forming bluffs. 3Bluffs What are the landforms produced at the middle course? Erosion at outer bank creates river cliffs The meanders migrate downstream. They remove the interlocking spurs on their way through ________. River cliffs erosion Bluffs

36 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 1Flood plains What are the landforms produced at the lower course? The load is carried to the valley floors by the flood water. Repeated flooding and __________ build up a flat area. deposition The deposits on the flood plain are called ________. They are fertile and good for farming. alluvium During floods, water overflows from the channel to the lands, bringing sediment with it _________ builds up on the river bed, silting occurs Sediment Flood plain

37 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 2Levees What are the landforms produced at the lower course? The flood water overflows from the channel. The (small / large) load is dropped at the river banks. The banks are (raised / collapsed). The levees are the ridge-like features at the river banks. Levee

38 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 3Deferred tributaries What are the landforms produced at the lower course? Tributaries flow _______ to the main channel. parallel They finally break through the ______ and join the main channel. levees Defferred tributary

39 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 4Oxbow lakes What are the landforms produced at the lower course? This is an oxbow lake. It is developed from a meander! Do you know how?

40 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 4Oxbow lakes What are the landforms produced at the lower course? Oxbow lakes are the product of active ______ erosion and ___________ in the river. lateral deposition When two outer banks of two bends meet, a new channel is formed. _________ silts the original channel. Sediment An oxbow lake is formed. Water flow The meanders bend more.The (outer / inner) banks are pushed backward Sediment Deposition Little water enters the old channel Oxbow lake

41 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 5Braided streams What are the landforms produced at the lower course? Water levels (rise / drop) during dry seasons. (Erosion / Deposition) forms low ridges and blocks the river flow. In wet seasons, the river is forced to split into several separated channels. Braided streams The braided streams rejoin

42 Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes Onshore current Deposits Onshore current New deposits during low-flow season Onshore current Distributary Lagoon Onshore current Mud-flat or marshes Delta forms 6Deltas What are the landforms produced at the lower course? A delta is a gently sloping platform of _________ gradually builds up and extends into the ____. sediment sea It is formed at the mouth of the river. The velocity of flow (rises / drops) It is a fan-shaped mud-flat.


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