2What are the main processes that operate in the upper course? What landforms occur in the upper course of a river?How are the landforms created?Learning objectives
3Processes of river erosion Erosion is the wearing away of the land.Study this photo.How do you think this river can erode the landscape?
4Processes of river erosion Hydraulic actionAttritionCorrosionAbrasion
5Definitions Hydraulic Action This process involves the force of water against the bed and banks.Abrasion/CorrasionThis is the process by which the bed and banks are worn down by the river’s load. The river throws these particles against the bed and banks, sometimes at high velocity.AttritionMaterial (the load) carried by the river bump into each other and so are smoothed and broken down into smaller particles.CorrosionThis is the chemical action of river water. The acids in the water slowly dissolve the bed and the banks.
11Interlocking spursIn the upper course the river does not have a huge amount of energy to erode as it does not have a high discharge and it has to transport large pieces of sediment.When the river meets areas of harder rock that are difficult to erode it winds around them. A series of hills form on either side of the river called spurs. As the river flows around these hills they become interlocked. So, a series of interlocking spurs are often found in the upper course of a river valley.
12Techniques! – 1. Fieldsketching…. Produce an annotated fieldsketch to show that this is part of an upland river valley.
132. OS MapsIdentify v-shaped valleys and spurs of land.
17How does a waterfall form? Rearrange the stages of formation into the correct order:
18Your labels should contain detailed explanations! WaterfallsDraw and annotate a diagram to explain the formation of a waterfall.Suggested labels:More resistant rockLess resistant rockPlunge PoolUnsupported rockFallen rocksGorgeYour labels should contain detailed explanations!
20Gulfoss Gulfoss is located in Southwest Iceland on the Huita River. Gulfoss has two ‘steps’ to its waterfall. These steps are made by basalt lava while the rocks between these layers are softer, sedimentary rocks.Its gorge is 70m deep and 3 km long!
21The geology of Gulfoss is more complex! grey basaltsandstonemudstonetillitegrey basaltconglomerateplunge poolWhich of these different rocks do you think is the most resistant?
22What are rapids and how do they form? Rapids are part of a river where the water is relatively shallow but the flow of the water is quite fast and turbulent as the water descends over a series of small steps.River RhôneRapids are formed due to a sudden steepening of the stream gradient, but without a sufficient break in slope to form a waterfall, or from the river flowing over a series of thin layers of hard and soft rock.
24Examination question Study the map of a river valley below: X Y Height (m)XYXYSketch a cross-section of the river valley from X to Y.Label two features of this river valley.State at what stage of a river’s course you would expect to find this type of valley. Give reasons for your answer.
26Key ideasErosion is the main process operating in the upper course of a river.The direction of erosion is vertical.There are four main types of erosion – hydraulic action, attrition, abrasion and corrosion.Valleys are v-shaped with interlocking spurs.Waterfalls are formed where a river meets a band of less resistant rock. Plunge pools and gorges are features associated with the formation of waterfalls.Rapids are smaller scale features formed where finer bands of varying resistance of rock are found.