Understanding Weathering and Erosion in Geology

1. Weathering and Erosion Chapters 14 & 18

2. WeatheringWatch Brain POP • The breaking down of rock • 2 types: mechanical and chemical

3. Mechanical Weathering • Rock is broken down by physical means • Types: • Ice wedging (freezing and expansion) • Abrasion (collision of rocks by wind, water, or gravity) • Organic activity (plant roots, digging of animals)

4. Abrasion

5. Chemical Weathering • Rock is broken down due to chemical interaction with the environment

6. Types of Chemical Weathering • Oxidation-elements in rock combine with oxygen, mostly in rocks with iron (rusting)

7. Types of Chemical Weathering • Hydrolysis-reaction of minerals in rock to water, turns rock into clay

8. Types of Chemical Weathering • Carbonation-carbon dioxide dissolves in water and creates carbonic acid (like in your soda!) • This acid causes slow break down of rock

9. Types of Chemical Weathering • Acid precipitation-water mixes with carbon dioxide and other air pollutants • Weathers rock • Air pollutants are often from burning fossil fuels

10. Rates of WeatheringDifferential Weathering: process by which softer, less weather-resistant rock wears away and leaves harder, more weather resistant rock. • Weathering occurs very slowly • Rates depends on many factors: • Rock composition • Amount of exposure • Climate • Topography and elevation • Human activities • Plant and animal activities

11. Rock Composition • Rocks containing calcite weather the quickest • Rate is determined by what material holds the sedimentary grains together

12. Amount of Exposure • More exposure=faster weathering • Larger surface area exposed=faster weathering • Fractures and joints create channels for more exposure

13. Climate • Areas with alternating hot and cold seasons have fastest rate of weathering • Areas that are hot and dry have the slowest rate of weathering

14. SoilWatch Brain POP: Soil • Mixture of minerals, gases, water, remains of dead organisms (humus) • Soil profiles show layers of soil called horizons • Humus • Climate determines soil formation

15. Soil Profile

17. ErosionWatch Brain POP • Products of weathering are transported • Soil erosion is caused by both natural and human activities (such as some farming) • Erosion keeps crops from growing and can cause famine • Roots of plants hold the soil in place • Agents of erosion include: wind, water, gravity, glaciers

18. Gravity and Erosion Mass movements caused by gravity: • rockfalls and landslides-very fast mvmt • mudflows and slumps-rapid mvmt • solifluction-slow, in cold regions • creep-very slow mvmt

19. Landslides

20. Slump Large block of soil and rock becomes unstable and moves downhill in one piece-occurs on very steep slopes

21. Erosion from wind • Sand grains get moved by a process called saltation (bouncing of grains by wind or water).

22. Effects of Wind Erosion • Deflation-removal of top soil and rocks • Deflation hollows-holes left from deflation • Ventifacts-rocks with smooth surfaces from wind abrasion

23. Wind Deposition • Dunes are formed when the wind slows down and drops the sand it is carrying

24. Wave Erosion • As wind moves over the ocean, wind produces waves and currents that erode the coastline.

25. Structures Formed from wave erosion • Sea cliffs • Sea caves, arches, stacks • Terraces See pgs 452-453

26. Stacks

27. Shoreline Erosion • Force of waves will break off rock and throw the pieces back on the shore creating abrasion (mechanical weathering) • Shoreline is also chemically weathered-air and salt water are forced into cracks in the rock

28. Beaches • A deposit of sediment along the shore • More sediment is deposited than removed

29. Farming and Erosion Prevention • Contour Plowing • Strip Cropping • Terracing • Crop Rotation These techniques help reduce the erosion caused by water flowing over the land.

30. Contour Plowing

31. Terracing