Process of scenery change

1. Process of scenery change Rivers in particular

2. Processes at work • From the source to mouth of a river three processes are taking place River erosion River Transport River Deposition

3. What is erosion? • Erosion is the way in which rock is worn away by something else, for example by wind or water or ice – these 3 are called agents of erosion – without them no erosion would take place. • It is not like weathering where the rock is broken down • [Can you remember the 3 types of weathering?] • There are 4 different ways water erodes the river away

4. Attrition is the collision of rock fragments in the water against one another. The rock particles are broken into smaller pieces and become smoother the longer the process continues. River Erosion 1

5. The results of attrition • See how these rocks are becoming smoother at the edges

6. Abrasion (or Corrasion,) is the grinding of rock fragments carried by the river against the bed and banks of the river. Remember – when you scrape your knee if you fall over – this an abrasion This action causes the channel to widen and deepen. This grinding is most powerful in flood time when large fragments of rock are carried along in the river bed. River Erosion 2

7. Corrosion is the process by which river water reacts chemically with soluble minerals in the rocks and dissolves them.  (although this is often called solution – confusing as solution is also a word used in transportation – so in general I don’t – but the animation you will see does!!!) We often say things like water pipes corrode – the chemicals in the water seem to eat them away! River Erosion 3

8. An additional process is also at work caused by the force of the water itself known as Hydraulic action. In this rocks are dragged away from the bed and banks by the force of the running water.  It is just like when you turn up a hose and point it at the ground – the soil and small stones get washed away River Erosion 4

9. Checkout this animation http://ysgol-rhyngrwyd.wikispaces.com/Unit+4+Changing+Earth It is also on http://www.bbc.co.uk/schools/gcsebitesize/geography/riverswater/riverprocessesrev1.shtml

10. A river carries or transports eroded materials such as mud, sand, boulders and dissolved materials on its journey. These materials are known as its load. The load is carried along by four processes. traction saltation suspension solution River Transport

11. River Transport 1 • Traction is where boulders or stones are rolled along the stream bed by the force of the water

12. River Transport 2 • Saltation is when small particles such as tiny pebbles are carried along in the river. • The small particles bounce along and leapfrog over each other.

13. River Transport 3 • Suspension is when very fine particles (suspension) such as clay, silt and fine sand are carried along in the river. • The small particles are held up by the water as they float because they are very, very small!

14. An example of suspension

15. River Transport 4 • Transportation in solution is when dissolved materials containing minerals like calcium and sodium are carried in the water and are invisible to the naked eye. • No picture here because you cannot see them!

16. Now go to the animation http://ysgol-rhyngrwyd.wikispaces.com/Unit+4+Changing+Earth It is also on http://www.bbc.co.uk/schools/gcsebitesize/geography/riverswater/riverprocessesrev2.shtml

17. A river drops its load when the speed or volume of the river decreases. The load, which it carries, is deposited. The heavier material is deposited first and the finer material carried further. Rivers reduce their speed when they enter flat land, enters a lake or the sea or reach an arid area. The volume can be reduced during a dry season or when the river passes over more porous landscapes e.g. sand or limestone. River Deposition

18. Do the River processes test quiz bite http://www.bbc.co.uk/apps/ifl/schools/gcsebitesize/geography/quizengine?quiz=riverprocessestest&templateStyle=geography