Chapter 4 - Erosion and Deposition

1. How can wind and water change our landscapes? Chapter 4 - Erosion and Deposition

2. Weathering- the destructive processes by which materials at or near the Earth’s surface are changed in color, texture, composition, firmness or form. Weathering is the beginning of erosion. • 1. Two types of weathering

3. a. Mechanical or physical weathering- a physical change in which rocks are broken into different shapes and smaller pieces (1) Six main processes can cause mechanical weathering (a) Impact and Abrasion- moving materials can cause rocks to fracture, flake or lose small particles

4. (b) Frost Action- water seeps into an opening or crack in a rock and then freezeswhen temperatures drop. Water expandswhen it freezes and causes rocks to break into pieces.

5. (c) Temperature- The cycle of heating and cooling of rocks causes a cycling of expansion and contraction that causes particles on the rock surfaces to crack or flake off. (d) Organic Activity- The roots of plants can often loosen and change rock material.

6. (e). Gravity can pull loosened rocks downhill resulting in a landslide causing rocks to break into smaller pieces.

7. (f) Exfoliation- Rocks which form under the surface form under pressure - confining pressure. When that pressure is released, the rock will expand. As it expands the outer layers break free in sheets, and is called exfoliation.

8. (2) All causes of mechanical weathering result in the breaking down of rocks into smaller pieces called sediments.

9. b. Chemical Weathering- changes in the chemical makeup or mineral composition of rocks • Five main processes can cause chemical weathering • (a) Water- can dissolve minerals holding rocks together, or form acids when mixing with gases in the atmosphere to form acid rain (speeds up decomposition of rocks)

10. (b) Oxidation- oxygen can chemically combine with substances resulting in the formation of a new substance (Ex. iron in rocks forming rust)

11. (c) Carbonation- carbon dioxide in the air can dissolve in rain forming carbonic acid which can dissolve certain rocks (Ex. limestone and feldspar)

12. (d) Sulfuric acid- sulfur oxides can combine with water producing acid rain which can chemically break down rocks, metals and other materials

13. Mayan ruins being destroyed by acid rain

14. (e) Plant acids- some plants produce weak acids that can dissolve minerals in rocks (Ex. mosses) (2) As chemical changes take place minerals can be added or removed from rocks.

15. Frayer Model • Compare Mechanical and Chemical Weathering Characteristics: Definition: Mechanical Weathering Nonexamples: Examples:

16. A. Erosion and Deposition 1. Erosion is the process by which weathered rock and soil are moved from one place to another.

18. 2. Erosion changes landscapes by wearing down mountains, filling in valleys, and making rivers appear and disappear. 3. Deposition is the process by which sediments are laid down in new locations.

20. 4. Weathering, erosion, and deposition act together in a cycle to wear down and build up Earth’s surface. 5. The agents of erosion are gravity, wind, running water, glaciers, and waves.

21. C. The Five Agents of Erosion and their Effects on Landscape 1. Gravity erosion or mass wasting- the downhill movement of sediments caused by gravity.

22. Mass wasting caused be gravity

23. a. Landslides- the tumbling of soil, rocks and boulders down a slope b. Mudflows- usually occur after heavy rains carrying large amounts of mud downhill Google Image Result for http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/Images/MSH80_boulder_left_by_lahar_muddy_river_09-16-80_med.jpg

25. c. Slump- materials such as rock or soil on a steep slope move downhill as a coherent unit to decrease the slope angle of land

26. Mass Wasting

27. Slump

28. d. Creep- the slow movement of sediments downslope, caused by repeated expansion and contraction of materials (Examples: freezing and melting, growth and decay of roots, burrowing animals)

29. Creep

30. Review Questions • 1. What is the relationship between erosion and deposition? Erosion- sediments are moved from one place to another. Deposition- Sediments are deposited in a new location.

31. 2. What are four examples of mass wasting? Answers Landslides Mudflows Slump Creep

32. 2. Running Water- runnoff, rivers, and streams are accountable for the greatest changes in Earth’s surface a. Runnoff- water moving across Earth’s surface picks up and carries particles of clay, sand, and gravel

33. Soil runoff into woods

34. 1. The amount of runoff is affected by the amount of rainfall, plant growth, and shape of the land.

35. 2. Urban storm water runoff effects water quality, water quantity, habitats, biological resources, public health and the aesthetic appearance of waterways. (a) After storms there is often a temporary increase in pollutants, toxins, and bacteria levels.

36. (b) Increased erosion and deposition results from large amounts of urban runoff which alters aquatic habitats.

37. Stream Bank Erosion

39. b. Streams (1) Streams usually cause erosion by abrasion (sediments colliding with rocks and wearing the rocks down over time) (2). Load- the soil particles and rocks carried by the stream

40. Load

41. (3) If a stream flows first over a hard rock layer, then a soft rock layer that is easily eroded, a waterfall forms.

43. (4) Downcutting represents downward erosion of the stream channel. It occurs when the stream energy (capacity) exceeds the stream's load, and causes valleys to be narrow and steep-sided (canyons and gorges).

44. (5) Lateral erosion undermines part of the bank or valley wall, leading to mass wasting and widening of the valley. (6) Stream deposition results from decreasing water velocity or from chemical changes. The coarsest material is deposited first as water velocity decreases. Stream deposited material is called alluvium.

45. c. River Systems- streams that join form rivers, which usually begin in mountains or hills (1) Larger steams flowing into a main river are called tributaries. (2) Eventually a river empties into another river, a lake, or an ocean at the mouth.

47. (3) The drainage basin is all of the area drained by a river and its channel. • Drainage basins are separated by divides (high ground between two drainage basins). • The Continental Divide is the largest divide, running north and south (close to Denver, CO).

50. (4) Deposits made by rivers are constantly changing the landscape of surrounding areas with sediments being deposited where a river curves, or meanders. (5) Oxbow lakes are small lakes formed from a U-shaped bend that erosion and deposition of sediments cuts off from the river.