Chapter 8

1. Chapter 8 Water Erosion and Deposition

2. 8.1 Surface Water • Explain what causes runoff • Compare rill, sheet, gully, and stream erosion • Discuss the three different stages of stream development • Describe how alluvial fans and deltas form

3. 8.1 Runoff • Runoff • water that does not soak into the ground or evaporate flows across the Earth’s surface • Part of the water cycle – Evaporation, condensation, precipitation, runoff, evaporation

4. 8.1 Runoff • Factors affecting runoff • The amount of rain • The more rain, the more runoff • The length of time • Longer periods results in more runoff • Slope of the Earth’s surface • Steeper the slope the more runoff • Amount of vegetation • Less vegetation results in more runoff

5. 8.1 The Effects of Gravity • Water will increase in speed by 9.8m/s • As water moves down a slope the water picks up speed and energy • Faster the water; the more erosion occurs

6. 8.1 Water Erosion • Rill and Gully Erosion • Rill erosion • Occurs when small streams form during periods of heavy rain • Leaves behind a small scar on the Earth’s surface • Over time rill erosion can become gully erosion • Gully Erosion • Occurs when a rill channel becomes broader and deeper • More erosion occurs than with rill erosion

7. 8.1 Water Erosion • Sheet Erosion • Water falls on a broad flat area • Water accumulates until it begins moving slowly • Occurs when rainwater flows into lower elevations, carrying sediments

8. 8.1 Water Erosion • Stream Erosion • Stream – water that continues to flow along a depression the water created • Water moves sediments from the bottom and sides of the steam • Stream becomes wider and deeper • River – stream wider than 12 feet

9. 8.1 River System Development • River Systems • Water in the river begins as precipitation that is transported through the following structures: • Sheet, rills, gullies, streams, rivers • Drainage Basin • The area that a stream receives its water • Eventually the water reaches the main river that drains into the ocean • Mississippi River basin is the largest U.S. basin

10. 8.1 Stages of Stream Development • Streams are defined as being classified as: • Young • Mature • Old • The stage is determined by the slope of the surface • The actual age doesn’t influence a stream’s classification

11. 8.1 Stages of Stream Development • Young streams • Steep sides • May have whitewater rapids and waterfalls • Found on steep slopes • Usually straight and narrow • Has a high energy level • Erodes on the bottom more than the sides

12. 8.1 Stages of Stream Development • Mature streams • Flows less swiftly through its valley • The energy begins to erode the sides • Begin to curve due to the varying speeds of the water

13. 8.1 Stages of Stream Development • Deeper water areas flow faster than shallow areas due to less friction • Areas of faster water erodes the sides faster forming curves called meanders • Areas where rocks are softer erode faster than the areas opposite the stream • The broad flat valley floor is called a floodplain • Usually covered by water when the stream floods

14. 8.1 Stages of Stream Development • Old Streams • Flows slowly through a broad, flat floodplain • Little erosion occurs due to the slope of the stream • River systems have streams of all ages

15. 8.1 Deposition by Surface Water • Sediments are deposited when the water loses its energy • Larger sediments settle out first • Smallest sediments are last to settle • Types of deposits • Alluvial fans • Usually found in at the base of a mountain valley • Deltas • The sediments are not deposited until it reaches the ocean

16. 8.2 Groundwater • Describe the groundwater system • Explain the effect that soil and rock permeability have on groundwater movement • Describe ways that groundwater erodes and deposits sediments

17. 8.2 Groundwater System Development • Water that soaks into Earth’s surface becomes part of the groundwater system • Between each particle of weathered rock in the soil are spaces called pores

18. 8.2 Groundwater System Development • Permeability • Soil and rocks are permeable when water can pass through them • The more pores present the more permeable the soil or rock • The more easily water can move • Clay has very few pores for water to travel through • Clay is impermeable due to the lack of pores

19. 8.2 Groundwater System Development • Groundwater Movement • Water continues to move downward until it hits impermeable rock called bedrock • Water begins to fill up the pores above the layer • An aquifer may develop • A layer of permeable rock that transmits water freely • The area of all pores are filled with water are called the zone of saturation • The upper surface is called the water table

20. 8.2 Wells, Springs, and Geysers • Wells • Water well – hole drilled through the Earth’s surface until the water table is reached and a pump pumps water to the Earth’s surface • Can go dry because water is removed faster than it is replaced

21. 8.2 Wells, Springs, and Geysers • Artesian well – a type of well that doesn’t need a pump • Requires a sloping aquifer between two impermeable layers • Increases the pressure of the area • Hole drilled in the surface can cause a fountain

22. 8.2 Wells, Springs, and Geysers • Springs • The area on Earth’s surface where the water table reaches the surface • Water is usually cold, but can be hot

23. 8.2 Wells, Springs, and Geysers • Geysers • A hot spring that erupts periodically, shooting water and steam into the air • Groundwater is heated to very high temperatures causing it to expand underground • Some water is pushed out of the ground • Remaining water boils quickly • Steam flows out of the opening pushing the remaining water out with it • Releases 40,000 liters (10,566 gal) once per hour

24. 8.2 Groundwater Erosion and Deposition • Acidic groundwater can dissolve limestone underground just as it can above ground • The space is dissolved over time until an underground opening is formed called a cave • Cave Formation • With erosion deposition must occur • Water evaporates and leaves behind a small amount of deposits on the ceiling called stalactites • Water drips to the floor evaporates and leaves behind deposits called stalagmites

25. 8.2 Groundwater Erosion and Deposition • Sinkholes • Underground rock near the surface is dissolved • Eventually the surface can’t support itself and collapses into the cave

26. 8.3 Water wars • Give examples of ways people use water • Explain why some communities must rely on water diversion for their water supply • Identify a problem caused by water diversion

27. 8.3 Water as a Resource • Average person uses 397 liters (105 gal) every day • Some communities must transport their water over great distances to support their use

28. 8.3 Water as a Resource • A bitter battle • Water that is transported to new locations may be needed to fill up water resources for other communities or natural resources

29. 8.3 Two Points of View • Conserve the natural resource • Decreasing water levels in natural resources • Increases the salt and mineral concentrations • Could cause organisms naturally found in these areas to be killed • Could lose the habitat organisms need to survive due to the lowered water levels

30. 8.3 Two Points of View • Water needed by people • Water needs to be diverted from natural areas to support human needs

31. 8.4 Ocean Shoreline • Describe forces that cause shoreline erosion • Compare and contrast different types of shorelines • List some origins of sand

32. 8.4 The Shore • Shoreline forces • Surface waves constantly move sediments back and forth • Waves are constantly eroding and depositing sediments • Longshore currents • Occurs when waves reach the shore at angles • Causes water to run parallel to the shore

33. 8.4 Sandy Beaches • Rocky shores are eroded by the waves crashing into them and the abrasion of the sediments being transported to form sand • Beaches • Deposits of sediments that run parallel to the shore • Deposits could be made from seashell fragments • Sand Erosion and Deposition • Sand can be moved by humans and storms besides waves

34. 8.4 Sandy Beaches • Barrier Islands • Sand deposits that parallel the shore but are separated from the mainland • Begin as a ridge of sand deposited by waves • Hurricanes and other storms can increase the amount of deposits to sea level or above • Wind blows the sand into dunes keeping it above sea level • Can last a few years or centuries, but always temporary