Presentation on theme: "2.3 How does a river shape the land along its different courses?"— Presentation transcript:
12.3 How does a river shape the land along its different courses?
2Can you find these kinds of landform at the same place? How do the characteristics of a river change along its course?Can you find these kinds of landform at the same place?
3They are different in _________ and _____ _______. What are the different sections along a river course?They are different in _________ and _____ _______.Upper courseMiddle courseLower coursegradientriverenergyRelatively straight, with bends around obstaclesWindingBig bends occur
4What are the different sections along a river course? Gradient of the upper course: ______steepGradient of the lower course: _______Gradient of the middle course: __________moderategentle
5What are the different sections along a river course? The energy and work vary along the three courses, different landforms are formed!Therefore, different landforms are found at different sections along a river course.Upper courseMiddle courseLower course
6Is this the impression you have for the upper course? What landforms are formed at the upper course?How much energy is there?What do you think about the energy of river at the upper course when compared with the middle and lower course? (Greater / Less)The energy is less because:Is this the impression you have for the upper course?The catchment areas of the tributaries at the upper course is (large / small). The amount of the channel water is (large / small).Large boulders in the channel (increase / decrease) the channel roughness.(Much / Less) of the energy are used for overcoming friction.
7What is the direction of the erosion at the upper course? What landforms are formed at the upper course?What is the direction of the erosion at the upper course?What is the work involved?________ erosion is the dominant work at the upper course.VerticalHeadward erosion also occurs when water starts to gather.Because of the small river energy, the rate of erosion is (slow / fast).The cross-section of a valley at the upper course(Small / Large) load can be transported.Deposition is (common / rare).
8Landforms at the upper course What landforms are formed at the upper course?What are the landforms produced?Landforms at the upper courseInterlocking spursRapidsPotholesGorgesWaterfalls
9How is the land shaped at the middle course? How much energy is there?Do you know why?How much energy is there at the middle course when compared with the upper course? (Greater / Less).More tributaries are joining the river.The amount of river water (increases / decreases).The river energy (increases/ decreases).The channel becomes _________. The water flows ______.smootherfaster
10How is the land shaped at the middle course? What is the work involved?The river flow is faster and with more energy.Why?(Erosion / Transportation / Deposition)What is the main work at the middle course?Erosion occurs, but there is extra energy for _____________.transportation
11Landforms at the middle course How is the land shaped at the middle course?What are the landforms produced?Landforms at the middle courseSlip-off slopesRiver cliffsMeandersBluffs
12Is the energy large or small at the lower course? What landforms are formed at the lower course?How much energy is there?Is the energy large or small at the lower course?
13The cross-section of s valley at the lower course What landforms are formed at the lower course?How much energy is there?It has the (smallest / largest) discharge among the three courses.The river bed is (smooth / rugged), so the friction here is greatly (reduced / risen).Therefore, the flows are at a (low / high) speed.The lower course has the (highest / lowest) energy.The channel here accommodates (less / more) water than that of the upper course.The cross-section of s valley at the lower course
14What 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.mouththe 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.
15What landforms are formed at the lower course? What is the work involved?Ha! Ha! All three work occur at the lower course!What is the work at the lower course?Erosion- at the (inner / outer) banks of the river.(Erosion / Transportation / Deposition)Transportation- bringing the load towards the mouth of the river.Deposition- whenever and wherever speed of flow is lowered.
16Landforms at the lower course What landforms are formed at the lower course?What are the landforms produced?Landforms at the lower courseFlood plainsDeferred tributariesOxbow lakesDeltasLeveesBraided streams
17Case study: How does the Chang Jiang change along different courses? Tuotuo HeYichangHukouUpper courseMiddle courseLower course
18Do you know any characteristics of the Chang Jiang? Case study: How does the Chang Jiang change along different courses?The longest river in China and ______ longest in the world.thirdDo you know any characteristics of the Chang Jiang?Average annual discharge: 30,000 m3/sec.The load is not heavy as compared with the __________.Huang HehumidsubtropicalIt flows past the ___________ _______ humid area of China.About % of the river water comes from _______.rainfall
19Case study: How does the Chang Jiang change along different courses? Middle courseLower courseUpper course
20What are the characteristics of the upper course of the Chang Jiang? The river source: The Tuotuo HeThe discharge is small.Vertical erosionThe Hutiaoxia at the Jinsha JiangThe gradient is gentle.The river flows slowly.At the Jinsha JiangSouth-flowing.The channel winds through interlocking spurs.The gradient is steep.
21What are the characteristics of the upper course of the Chang Jiang? At the Sichuan PendiMore rainfallMany large tributaries join the main channelDischarge increases rapidlyGreat erosive powerForms Sanxia
22What are the characteristics of the middle course of the Chang Jiang? A big drop in _______ and the _________.altitudegradientMeanders are formed.286 kmNumerous lakes are found, e.g. Dongting Hu.Length of the river between them: 712 km
23What 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.
24How 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 ________.inputsprocessesoutputsOpen systemClosed systemInputProcessesOutputEnergyEnergyEnergyEnergyMatterMatterBoundary of the system
25How does a river basin work as a system? InputsProcessesOutputs Weathering Mass movement Erosion Interception Drip flow/ Stem flow Surface run-off Infiltration Subsurface run-off Transportation DepositionRadiationAbsorptionConductionSolar radiationHeatEvaporationChanneloutflowWaterPrecipitationWaterEvapo-transpirationVapourExogeneticprocessesRocksTransportationSediment
27What are the landforms produced at the upper course? 1 Interlocking spursThey are the spurs interlocking with each other.The river has too little energy to remove obstacles, so the river water flows around them.Interlocking spursValley is deepened________ erosion deepens the channel and makes the obstacles more marked.Vertical
28What are the landforms produced at the upper course? 2 GorgesDowncutting is (slower / faster) than lateral erosion.This creates a (deep / shallow) and (narrow / wide) V-shaped valley, i.e. gorges.
29What are the landforms produced at the upper course? 3 RapidsThe river water is unable to erode the layer of _________ rock.resistantRapidsThe river bed becomes (even / uneven).The turbulent currents are called rapids.
30What are the landforms produced at the upper course? 4 WaterfallsLess resistant rock is eroded by river water at a (slower / faster) rate.Water flowWaterfall formsThe river falls vertically down.Plunge pool formsThe falling water produces strong _________ action, forming a circular hollow filled with water.Large angular bouldershydraulic
31Which type of fluvial erosion is involved within the potholes? What are the landforms produced at the upper course?Which type of fluvial erosion is involved within the potholes?Abrasion.5 PotholesHow does it form?What is this?PotholeWhen a river flows over an uneven surface, it causes ___________ in the water.turbulenceA pothole is formed when the water drills with the load it carries.
32What are the landforms produced at the middle course? 1 Slip-off slopes and river cliffsWhat are the two landforms produced?What are the work involved at the inner and outer bank?Which part of the river has the fastest flow?River cliffInner bank: __________depositionOuter bank: ______________Slip-off slopelateral erosionFastest part of the river flowRiver cliffSlip-off slope
33What are the landforms produced at the middle course? 2 MeandersThe outer bank gets worn away through _______.Inner bankOuter bankerosionMeander appearsMore convexMore concaveThe inner bank builds up through __________.Lateral erosion creates river cliffsdepositionSlip-off slopes formThe river (bends/ straightens).Each bend is called a meander.Faster stream of water thrown towards outer banksSedimentLow river cliff
34What are the landforms produced at the middle course? 3 BluffsThe meanders migrate downstream.Erosion at outer bank creates river cliffsThey remove the interlocking spurs on their way through ________.erosion__________ at outer bank are pushed back and join into lines, forming bluffs.River cliffsBluffs
35What are the landforms produced at the lower course? 1 Flood plainsThe load is carried to the valley floors by the flood water.Repeated flooding and __________ build up a flat area.During floods, water overflows from the channel to the lands, bringing sediment with it_________ builds up on the river bed, silting occursSedimentdepositionThe deposits on the flood plain are called ________. They are fertile and good for farming.Flood plainalluvium
36What are the landforms produced at the lower course? 2 LeveesThe flood water overflows from the channel.The (small / large) load is dropped at the river banks.LeveeThe banks are (raised / collapsed).The levees are the ridge-like features at the river banks.
37What are the landforms produced at the lower course? 3 Deferred tributariesDefferred tributaryTributaries flow _______ to the main channel.parallelThey finally break through the ______ and join the main channel.levees
38What are the landforms produced at the lower course? 4 Oxbow lakesThis is an oxbow lake It is developed from a meander! Do you know how?
39What are the landforms produced at the lower course? 4 Oxbow lakesOxbow lakes are the product of active ______ erosion and ___________ in the river.Water flowLittle water enters the old channelSedimentlateralDepositiondepositionThe meanders bend more.The (outer / inner) banks are pushed backwardWhen two outer banks of two bends meet, a new channel is formed.Oxbow lake_________ silts the original channel.SedimentAn oxbow lake is formed.
40What are the landforms produced at the lower course? 5 Braided streamsWater levels (rise / drop) during dry seasons.(Erosion / Deposition) forms low ridges and blocks the river flow.Braided streamsIn wet seasons, the river is forced to split into several separated channels.The braided streams rejoin
41What are the landforms produced at the lower course? 6 DeltasA delta is a gently sloping platform of _________ gradually builds up and extends into the ____.sedimentOnshore currentOnshore currentOnshore currentOnshore currentseaMud-flat or marshesDistributaryIt is a fan-shaped mud-flat.DepositsNew deposits during low-flow seasonLagoonIt is formed at the mouth of the river.Delta formsThe velocity of flow (rises / drops)Onshore current