Chapter 7 – weathering, erosion, & soil

1. Chapter 7 – weathering, erosion, & soil Started 3-13-14

2. Weathering Process in which rocks breakdown and change Erosion Removal and transport of weathered material from one location to another Weathering and Erosion

3. 2 types of weathering 1. Mechanical – aka physical weathering, when rocks and minerals break into smaller pieces 2. Chemical – when rocks and minerals have changes in their composition (or make-up) as a result of chemical reactions

4. Factors affecting mechanical weathering 1. Temperature • When water freezes it expands and increases in volume by ~9% (extra credit opportunity here) • Water in cracks of rocks can cause rocks to split by exerting pressure when freezing and expanding. • Repeated thawing and freezing of water in cracks of rocks is frost wedging

5. Frost wedging can cause potholes

6. Factors affecting mechanical weathering 2. Pressure • Bedrock (hard, solid rock beneath surface materials such as soil or gravel) can be under a lot of pressure from overlying rocks but when the top layers are removed, the bedrock surface can expand and crack. • Exfoliation can also occur – outer layer of rock is stripped away • Plant roots can exert pressure on rocks and split through them.

7. Tree roots splitting rocks

8. Physical Weathering Rates • Occurs in cool, dryer climates, when water undergoes repeated freezing and thawing

9. Factors or agents affecting chemical weathering • Water • Oxygen • Carbon dioxide • Acids *Temperature – determines rate of chemical reactions (higher temp. = faster reaction rate) * The composition of the rock will determine the effect the chemical weathering will have on it.

10. Water • It can dissolve many kinds of minerals and rocks (solvent) (it plays in active role in some reactions and serves as a medium through which other reactions occur) • Hydrolysis – reaction of water with other substances

11. Oxygen • Combines with other substances – oxidation • Rust = oxygen and iron in presence of water or air moisture

12. Carbon Dioxide and Water • CO2 is produced by living organisms during respiration • Carbonic Acid is created when CO2 and H2O are combined, and falls to the Earth as precipitation • Carbonic Acid – dissolves limestone and marble

13. Acid Precipitation • Human activities • Burning of fossil fuels • Car emissions Oxidation of sulfur dioxide & nitrogen oxides

14. Variables of climate that affect Chemical Weathering • Precipitation • Temperature • Evaporation

15. rate of Chemical weathering • Rock type and composition • Warm temp., lots of rainfall, & lush vegetation = produces a lot of organic matter = carbon dioxide produced… • Topography – materials on slopes more affected because of gravity

16. The rock that weathers the fastest • SEDIMENTARY

17. Surface Area • The greater the surface area the greater the increase in weathering

18. Section 7.2 Erosion and Deposition

19. Deposition • Transported materials by the process of erosion are settled on theground or sink to the bottom of a body of water • Final stage of erosional process

20. Gravity’s role on Erosion • Force of gravity tends to pull all materials down a slope • Glaciers have the power to move large particles of weathered material

21. Rill Erosion Running water in small channels on side of a slope Newer Gully Erosion Channels are large, deep and wide Can be more than 3 meters deep Erosion

23. Streams • Carry billions of metric tons of sediments and weathered materials to coastal areas • Mississippi River alone carries 750 million metric tons into the Gulf of Mexico

24. Deltas • A river enters a large body of water • Volume of river flow and action of tides determine the shape of the delta

25. Sandbars • Sand along a shoreline is repeatedly being picked up, moved, and deposited by ocean currents • If sand continues to build up it can create a barrier island

26. Glacial Erosion • Erosional effects are large scale and dramatic • Scrape and gouge out large sections of the Earth’s landscape

27. Wind Erosion • Limited precipitation and high temperatures • Little vegetative cover to hold soil in place

28. Wind Barrier • Trees or other vegetation sometimes planted to diffuse the direction of the wind • Reduce wind force over land surfaces • Wind erosion is insignificant when compared to running water and glacial activity

29. Section 7.3 Formation of Soil

30. SOIL • LOOSE COVERING OF BROKEN ROCK PARTICLES AND DECAYING ORGANIC MATTER (humus) OVERLYING THE BEDROCK OF EARTH’S SURFACE

31. Soil for life • Food • Oxygen (plants) • Clothing/shelter • Protects from pollution (filter)

32. Soil – its everywhere • But • On steep mountain slopes • Extremely cold regions

33. 3 Processes form soil • Chemical weathering • Mechanical weathering • Biological activity

34. Parent Rock • Solid bedrock from which weathered pieces first break off

35. Top layer • Smallest weathered pieces of rock; living and dead organisms • Rainwater seeps through the top layer and carries dissolved minerals to lower layers of soil

36. 2 types of soil • Residual soil – located above its parent material • Transported soil – moved to a location away from its parent bedrock

37. Soil profile • Vertical sequence of soil layers – can be seen when heavy machinery digs out a chunk of soil • Soil horizon – A distinct layer or zone within a soil profile

38. A Horizon • High concentrations of organic matter and humus • Soils rich and usually dark colored

39. B Horizon • Less developed soil • Subsoils enriched w/clay materials • Can have accumulation of clay forming a hard material that doesn’t allow much water to pass • Accumulation of minerals washed down from the topsoil • Red or brown in color from the presence of iron oxides

40. C Horizon • Less developed • Weathered parent material

41. Topography • Sloped areas – thin soil, coarse, and infertile • Due to the runoff that occurs • South facing slopes receive more sunlight which creates more vegetation and thicker soil

42. Soil Types • Appearance, rate of formation, and productivity are determined by climate • Types of organisms • Topography • Length of time

43. Soil Types • Polar – usually shallow soil • Temperate - vary • Desert – high salt due to lack of water • Tropical – weathered & often infertile

44. Types in the US • Temperate • Desert • Tropical • Polar • Mixed

45. Soil Fertility • The measure of how well a soil can support the growth of plants • Effects • Mineral nutrients • Number of microorganisms • Precipitation • Topography • Acidity

46. Soil Color • Is determined by composition and climate • The most fertile soil is dark – rich in humus

47. Assignment • Use the soil textural triangle to make your own data chart (see page 172 for a reference) and write at least 5 good questions about your data chart that a group of partners could answer using your data and the textural triangle.