Presentation on theme: "The River Course Features of the Upper Course Potholes Waterfalls"— Presentation transcript:
1 The River Course Features of the Upper Course Potholes Waterfalls RapidsFeatures of the Lower CourseFlood PlainMeandersOx Bow LakesLeveesEstuaries and DeltasRiver TerracesFeatures of the Middle CourseFlood PlainMeanders
3 Formation of a Waterfall Resistant, hard rock lies on top of softer rock type in a river channel.The underlying softer rock is eroded more quickly than the harder rock and so the resistant rock is undercut.Over time the resistant rock will become increasingly unsupported.The harder rock will eventually collapse under its own weight.Once it has collapsed, the rocks which have shattered will be swirled around at the base of the waterfall, due to the force of the water.This will cause the formation of a plunge pool at the base of the waterfall.This process will happen continuously, causing the waterfall to move backwards (retreat).Waterfall retreats upstreamOverhang collapsesHard RockSoft RockPlunge pool developsundercuttingWhere the 2 layers of rock are very thin, there will be no obvious collapse, so the water will just swirl round, causing rapids
4 Formation of a Flood Plain The river widens its valley by lateral erosion (horizontally)The river uses much of it’s energy transporting large quantities of materialWhen the river floods, after a period of heavy rainfall, the alluvium (sedimentary deposits) are spread across the valley floor, and deposited.Every time the river floods another layer of alluvium is deposited and a flood plain is formed.When the river is losing energy, for example after a flood, the coarsest, heaviest material is deposited first, as this uses the most energy to transport.Over time this can form a natural embankment, called a levee.
5 Formation of a MeanderIn every river channel, even very straight channels, riffles and pools develop.Pools are deeper stretches of slow moving water, usually with fine alluvial depositsRiffles are shallower sections of faster flowing water, flowing above coarser materialOnce pools and riffles have developed in a river channel, the river swings from side-to-sideThis side-to-side motion is then assisted by erosion and deposition of the river channelThe meander becomes more curved as a result of erosionErosion occurs on the outside bend where velocity is strongest and the water is deepest.On the other side, deposition occurs, where the current is weakestOver time, the meander becomes more and more curved, due to erosion and deposition, but also because of the movement downstream.
6 Formation of an Ox Bow Lake Oxbow lakes form during periods of floodThe water is looking for the fastest, most direct route and so instead of flowing round the meander, it cuts straight across.Eventually the water inside the Oxbow lake will either evaporate or silt up
7 Task 1: Describe fully, with the aid of an annotated diagram, how one of the following riverfeatures is formed:WaterfallFlood PlainMeanderOx Bow Lake (6)
8 Formation of a River Terrace During glaciation, the land was pushed downwards under the weight of the massive ice sheetsSince the ice age ended, the land has been slowly rising to its former positionRivers try to adjust to this by eroding back into its former flood plainAreas of the floodplain remain as river terraces
9 Formation of Estuaries and Deltas When a river enters the sea its flow characteristics become very differentVelocity is reduced, and the load has been depositedThe mouth of the river broadens to form an estuaryTides sweep up the mouth of the river clearing it of any remaining material, which is then taken into the seaThe sediments that is not transported into the sea from the estuary forms sand and mud banks
10 Task 2:For either a River Terrace or an Estuary,describe in detail, how it is formed(4)