Weathering, Erosion, & soil

1. Weathering, Erosion, & soil Ch-12

2. Weathering • Break up of rock into smaller particles • Two types of weathering • Mechanical Weathering • Breaking a rock into smaller pieces of the same thing • Chemical Weathering • Rock broken down into something else

3. Types of mechanical weathering • #1 ice or frost wedging (freeze thaw) • water expands when it freezes • pries things apart • #2 abrasion • Two types • Rocks tumbling by gravity or streams • Glaciers grinding • #3 plants • Roots pry

4. #4 animals • dig holes that allow in elements and bring rocks to the elements • #5 uplift and weight reduction • rocks pushed up • releasing the pressure of the weight • rock expands • cracks off outer layers in sheets • called exfoliation

5. Types of Chemical Weathering • #1 water (hydrolysis) • water contains some acids or is a universal solvent by itself • acids get into water by • carbon dioxide, decaying bodies, sulfur in air • dissolves the material or molds it into something else • Ex- some acids dissolves limestone forms caves • Ex- water dissolves some minerals into clays

6. #2 oxygen (oxidation) • rusting

7. What determines the rate of weathering • Exposure • More = higher rate • Composition • More porous = higher rate • Climate • Warm and moist = higher rate • Dry = low rate

8. Soil • Small rock particles crushed up with dead organic matter • Made from parent material • the rock the soil forms from • Categories of soil • Residual • Soil that resides above the rock it was formed from • Transported • Soil that does not reside above the rock it was formed from

9. Soil Profile • What it looks like when you look at a dug hole • Three layers called horizons • “A” horizon • Contains topsoil • Darker • Smaller particles • Contains more humus (organic matter)

10. “B” horizon • Called subsoil • larger rock size • Contains some humus that leached from “A” • “C” horizon • little weathering of rock • bedrock directly below it

11. Soil Composition • determined by • Time – (More = more weathering) • Parent rock – (give some characteristics) • Plants and animals – (supply humus & control weathering rate) • Topography – (water flows downhill could wash soil away and does not have enough time to mature • Climate – (warm & moist have the best soil)

12. How Material is transported • Mass movement = movement down slope by gravity • Erosion = removal by wind, running water, or some other natural agent

13. Types of Mass Movement • #1 landslide • downhill movement of loose soil • #2 creep • Slow movement by freeze thaw action • #3 slump • whole section slides leaving a curved scar • slope too steep to hold soil up

14. #4 earthflows • saturated earth flows downhill • velocity varies due to • types of soil and amount of moisture • #5 mudflows • Rapid down slope movement • soil in water • Ex)  lahar

15. Conservation of Soil • soil needs to be left covered to stop erosion and diminish mass wasting • We are loosing soil 17 times faster than it can be replaced

16. Farming Practices • Contour plowing • plowing with the grain of the land • No-till • do not plow the ground, leaves ground cover • Windbreaks (hedgerows) • Stops the wind from gaining momentum • Terraces • slows the flow of water

17. Strip-cropping • alternate crop and grass • slows the water • acts as filter • Diversion ditches • Slows water and takes it off the field

18. Construction Practices • Silt fences • To catch runoff • Containment ponds • slows water discharge • Riprap • large boulders placed on the river bank to control erosion