Erosion – 21.2

1. Erosion – 21.2 Water Erosion

2. Erosion – process by which weathered material is transported • Common agents of erosion – gravity, wind, glaciers, running water

3. Stream Erosion • Water is constantly changing from one form to another through the water cycle • Rivers flow into oceans • Evaporates back to vapor in atmosphere • Falls on land as precipitation • All this movement – has the energy to carry and move sediment • Sediments is REMOVED from one location and DEPOSITED at another location

4. Parts of a River System • Main River • Tributaries – feeder streams that flow into main stream • Meanders – winding pattern of curves • Flood Plains - part of the valley floor that can be covered by water during a flood

5. Parts of a River • Channel – relatively narrow depression that a stream follows as it flows downhill • Banks – edges of a stream channel above water level • Stream Bed – part of channel that is below the water

6. Stream Load – material carried by a stream Suspended Load – velocity of stream keeps them from sinking Bed Load – larger, coarser materials- move by sliding and jumping along the bed Dissolved Load – mineral matter that has been dissolved and transported in solution

7. How much a river can carry depends on how much water and how fast it is moving. Headwaters – steep gradient, so has high velocity causing rapid channel erosion Mouth – gradient becomes flatter, velocity decreases, has less erosive power

8. Rivers with low gradients tend to have more bends • As river slows down, less energy is available to erode the stream bed • More energy is directed at the banks • Erosion around the bends and curves in meanders

9. Meanders can become so curved – form a loop or an oxbow lake

10. Stream Deposition • As velocity decreases the stream can’t carry as much sediment – so some sediment gets deposited • Can deposit sediment on land or in water

11. River Delta • As stream enters a large body of water such as an ocean or lake, velocity decreases suddenly – load is deposited in triangular pattern – called a Delta

12. Alluvial Fan • As stream descends slopes of mountains or hills and reaches a flat plain – speed suddenly decreases. • Stream deposits some of its load on the level plain at the base of the slope • Fan shaped deposit – Alluvial Fan

13. Flood Plain Deposits • As stream floods and spreads out – loses velocity and deposits sediments on the flood plains

14. Wave Erosion • Power of waves striking rock on shoreline – can sometimes shake ground as much as a small earthquake. • Force of waves break off pieces of rock and throw pieces back against shore. • Abrasion – reduces the rocks to pebbles and sand grains. • Usually takes place during storms • Also have chemical weathering due to salt content of sea water

15. Erosional Landforms

16. Longshore Currents Transportation of sand along shoreline Will keep moving until shoreline changes direction

17. Does the stream below have a relatively steep gradient or a shallow gradient?

18. Does the stream below have a relatively steep gradient or a shallow gradient?

19. Do the following pictures show examples of stream erosion or stream deposition?

20. Do the following pictures show examples of stream erosion or stream deposition?