1. Weathering
Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down
Erosion - process of removing Earth materials from their original sites through weathering and transport

2. Weathering
Mechanical Weathering - processes that break a rock or mineral into smaller pieces without altering its composition
Chemical Weathering - processes that change the chemical composition of rocks and minerals

3. Processes and Agents of Mechanical Weathering
These are actions or things that break down Earth materials
frost wedging
thermal expansion and contraction
mechanical exfoliation
abrasion by wind, water or gravity
plant growth
salt crystal growth between rocks

4. Processes and Agents of Mechanical Weathering
Frost Wedging – cracking of rock mass by the expansion of water as it freezes in crevices and cracks

5. Frost Wedging (in soil)
Ice crystals

6. Processes and Agents of Mechanical Weathering
Thermal expansion and contraction –
repeated heating and cooling of materials cause rigid substances to crack and separate

7. Processes and Agents of Mechanical Weathering
Exfoliation – As underlying rock layers are exposed, there is less pressure on them and they expand. This causes the rigid layers to crack and sections to slide off (similar to peeling of outer skin layers after a sunburn). The expanding layers often form a dome.

8. Dome Exfoliation

9. Processes and Agents of Mechanical Weathering
Abrasion – Moving sediments or rock sections can break off pieces from a rock surface they strike (friction). The sediments can be moved by wind or water and the large rock sections by gravity.

10. Wind Abrasion

11. Water Abrasion

12. Wind and Water Abrasion
Photo Ref: P211442, "IPR/52-34CW BGS©NERC

13. Processes and Agents of Mechanical Weathering
Plant Growth – As plants such as trees send out root systems, the fine roots find their way into cracks in the rocks. As the roots increase in size, they force the rock sections apart, increasing the separation and weathering.

14. Plant Wedging

15. Plant Wedging

16. Salt Crystal Growth

17. Chemical Weathering
The process by which rocks and minerals undergo changes in their composition as a result of chemical reactions.

18. Factors in Chemical Weathering
Climate – wet and warm maximizes chemical reactions
Plants and animals – living organisms secrete substances that react with rock
Time – longer contact means greater change
Mineral composition – some minerals are more susceptible to change than others

19. Processes of Chemical Weathering
Dissolving (dissolution)
Oxidation
Hydrolysis

20. Processes of Chemical Weathering
Dissolving (dissolution)
Water, often containing acid from dissolved carbon dioxide, will dissolve minerals from a rock body leaving cavities in the rock. These cavities may generate sinkholes or cave features such as stalactites and stalagmites.

21. Water’s Effects
Water weathers rock by dissolving it

22. Limestone cave feature result of dissolution

23. Water’s Effects Caves and caverns typically form in limestone
Speleothems - cave formations; made of calcite
form a rock called travertine
stalactites - from ceiling
stalagmites - on ground

24. Karst Topography
A type of landscape in rainy regions where there is limestone near the surface, characterized by caves, sinkholes, and disappearing streams.
Created by chemical weathering of limestone

25. Water Affects
Karst topography forms on limestone terrain and is characterized by:
caves/caverns,
sinkholes,
disappearing streams,
springs

26. Features of Karst: Caves

27. Features of Karst: Disappearing Streams

28. Water Leaching
It is the process by which H2O carries dissolves minerals to lower layer of rock

29. Processes of Chemical Weathering
Oxidation
Minerals may combine with oxygen to form new minerals that are not as hard. For example, the iron-containing mineral pyrite forms a rusty-colored mineral called limonite.

30. Pyrite Oxidation Pyrite Limonite
Pyrite
Limonite

31. Iron Oxidation
Oxygen combines with iron-bearing silicate minerals causing "rusting"
Iron oxides are red, orange, or brown in color

32. Processes of Chemical Weathering
Hydrolysis
Minerals may chemically combine with water to form new minerals. Again these are generally not as hard as the original material.

33. Feldspar Hydrolysis Feldspar Kaolinite (clay)
Feldspar
Kaolinite (clay)

34. Carbon Dioxide Affects
CO2 is produced by living organisms in the process called respiration
CO2 forms a weak carbonic acid when combined with precipitation
Carbonic acid reacts with minerals such as calcite in limestone and marble to dissolve rocks

36. Acid Precipitation Affect
Mainly known as acid rain
Sulfur dioxide is formed from the industrial burning of fossil fuels
Nitrogen oxides are emitted from car exhaust
Each combine with H2O and O2 in the atmosphere to form sulfuric and nitric acids

37. Acid Rain has a pH less than 5.6

38. Acid Rain
Compounds from burning coal, oil and gas react chemically with water forming acids.
Acid rain causes very rapid chemical weathering

39. Acid Precipitation and Fish

40. Biological Action Lichens, fungi, and other micro-organisms
Chemically and physically change rock

41. Factors Affecting Weathering
Mineral Composition
Least stable
Olivine
Ca plagioclase feldspar
Pyroxene
Amphibole
Biotite
Na plagioclase feldspar
Potassium feldspar
Muscovite
Quartz
Most stable
*Surface Area
Texture
Temperature
Humidity
Plant growth
Topography
Time

42. There is a higher rate of mechanical and chemical weathering in Asheville than in Phoenix.

43. Climate and Chemical Weathering

44. Factors Affecting Weathering
*Surface Area
Texture
Temperature
Humidity
Plant growth
Topography
Time
Mineral Composition
Least stable
Olivine
Ca plagioclase feldspar
Pyroxene
Amphibole
Biotite
Na plagioclase feldspar
Potassium feldspar
Muscovite
Quartz
Most stable

45. Factors Affecting Weathering
Type of material – both are from 1780’s; one is slate, the other is marble. Which is which? Why is there a difference?

46. Factors Affecting Weathering
Surface Area – Most important
Smaller particles, more surface area
Examples
Crushed ice cools faster
Granulated sugar dissolves faster
More exposed rocks weather more

47. Factors Affecting Weathering
Differential weathering is when rocks weather at different rates
Caused by different mineral compositions
Sedimentary rocks weather more easily than igneous rocks