Edexcel IGCSE Geography Chapter 1 - Pearson Schools

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V-shaped valley –cross-sectionriver has been cut downby vertical erosionDepositionDeposition is the laying down of material transported by the river. This occurswhen there is a decrease in the energy, speed and discharge of the river. Thisis most likely to happen when a river enters a lake or the sea. It will alsohappen wherever there is a decrease in the gradient of the river’s channel.<strong>Chapter</strong> 1: River environmentsAKeyS – interlockingspursBhard cap rock –difficult to erodesofter rock –easier to erodeChard rockoriginal positionof waterfallmass movement ofmaterial down thevalley sidesriver cutting downriver cutting downriver swings fromside to sidegorgewaterfall retreatsplunge poolpresent waterfallgorgedirection ofwaterfall retreat1.5 River landformsThe long profile of a river runs from its source to the point where it entersthe sea, a lake or joins another and larger river. The character of the longprofile changes downstream. Overall it has a smooth concave shape. It is steepand in places irregular where the river is flowing well above sea level inupland country. The irregularities occur where hard rock outcrops run acrossthe valley. Natural lakes and reservoirs can also disrupt the smoothness of thelong profile. However, the profile becomes much gentler and smoother as theriver runs through lowland country and reaches its destination. Changes inthe character of river landforms are associated with these changes in the longprofile. For this reason, we should distinguish between upland and lowlandriver landforms.Upland landformsThe main river landforms found in upland areas are: steep V-shaped valleys,interlocking spurs, waterfalls and gorges (see Figure 1.12). They have allbeen formed mainly by the processes of river erosion already described in Part1.4. The processes of weathering and mass movement have also played a part.In the uplands, the long profile is steep and the river flows fast. Much of theriver’s energy is spent cutting downwards. The processes of hydraulic action(erosive force exerted by water) and abrasion, in particular, erode the river bedand thus make the valley deeper (Figure 1.12A). Because of the steepness anddeepness of the valley, there is mass movement of material down the sides ofthe valley. Some of this material becomes river load and helps the abrasionprocess. The valley floor is narrow and often completely occupied by the river.Interlocking spurs are formed where the river swings from side to side(Figure 1.12B). Again the main work of the river is vertically downwardsinto its bed. This means that the river cuts down to flow between spurs ofhigher land on alternate sides of the valley.Waterfalls occur where a band of hard rock outcrops that is much moreresistant to erosion than the softer rock below it (Figure 1.12C and D). Thissofter rock is readily eroded by the force of the water as it falls over the hardcap rock. Gradually, the falling water excavates a plunge pool at the bottomof the falls. Slowly the hard rock is eroded back by the river and so thewaterfall gradually retreats upstream leaving a gorge below it. The gorge isprotected from being widened by its capping of hard rock. The Iguaça Falls inSouth America are a spectacular example and attract many tourists(Figure 1.13).DFigure 1.12: The origin of river landforms in upland areas10
KeyDifference inheight betweenX and Y is 82 metresBRAZILNinternational borderroadairporthotelIguaçu NationalPark, southern BrazilIguaça RiverARGENTINAARGENTINAYIguaçuXFalls0 2 4 6 8 10 kmFigure 1.13: Map and photograph of the Iguaçu FallsLowland landformsThe river and its landforms change when the river leaves the uplands and flowsacross lowlands (Figure 1.14). The river channel becomes wider, deeper andsmoother. Because of this, both the velocity (speed) and discharge of the rivercontinue to increase, despite the gentler gradient. The river course in plan (map)view becomes less straight and is characterised by a series of meanders. The valleycross section is wider and flatter. The floor is occupied by a floodplain with itsdistinctive levees, meanders and ox-bow lakes (Figure 1.15). Near the end of itscourse, the flood plain spreads out to become either a delta or an estuary.<strong>Chapter</strong> 1: River environmentsPlan of the riverUplandsLowlandsdeltadistributariesmeanderox-bowlakeChannelcrosssectionChannelcrosssectionsmaller loadmaterialwide and deeprockValleycrosssectionriverValleycrosssectionalluvium or siltleveesfloodplainFigure 1.14: River and valley features11
Page 1 and 2: Section A:The natural environment a
Page 3 and 4: ●●●●overland flow - most of
Page 5 and 6: shows the channel networks of two d
Page 7 and 8: There are a number of factors affec
Page 9: ErosionThere are several different
Page 13 and 14: As lateral erosion continues, the b
Page 15 and 16: The height of the drainage basin an
Page 17 and 18: ●●●The rising standard of liv
Page 19 and 20: uses less water (now 14%) (Figure 1
Page 21 and 22: 1.7 Water qualityIn Part 1.6, we lo
Page 23 and 24: Agriculture●●●Liquid from far
Page 25 and 26: There is a fourth and relatively ne
Page 27 and 28: FACTORPhysicalWeatherRockSoilRelief
Page 29 and 30: In the longer term, there is the co
Page 31 and 32: the monsoon climate with its heavy

Edexcel IGCSE Geography Chapter 1 - Pearson Schools

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