1. Ch 5 – Weathering & Erosion
Objectives
Briefly contrast weathering and erosion.
Contrast chemical and mechanical weathering.
List and describe the types of mechanical weathering.
List and describe the types of chemical weathering.
List the products resulting from the chemical weathering of Igneous rocks.
List and discuss the factors that influence the type and rate of rock weathering.

2. The Rock Cycle This Unit – Ch 5 & 6 Last Unit – Ch 3 &4
What kinds of rock can be melted? Can be weathered & eroded? Heated & Pressurized?

3. Weathering Breakdown of rock due to surface processes
2 types of weathering
Mechanical
Chemical

4. Physical Weathering Abrasion - wind & water
Frost wedging - water expands when it freezes
Exfoliation or unloading –
rock breaks off into leaves or sheets along joints which parallel the ground surface;
caused by expansion of rock due to uplift and erosion; removal of pressure of deep burial
Thermal expansion -
repeated daily heating and cooling of rock;
heat causes expansion; cooling causes contraction.
different minerals expand and contract at different rates causing stresses along mineral boundaries.
Plant Roots – break rocks apart as they grow
Salt Crystal Growth – evaporation, crystals grow between rocks

5. Type of physical weathering?

6. Type of physical weathering?

7. Type of physical weathering?

8. Type of physical weathering?

9. Type of physical weathering?

10. Type of physical weathering?

11. Type of physical weathering?

12. Type of physical weathering?

13. Chemical Weathering
Rock reacts with water, gases and solutions (may be acidic); will add or remove elements from minerals.
1. Dissolution (or solution)
- also includes leaching
2. Oxidation – RUST!
3. Hydrolysis
4. Biological Action
5. Spheroidal

14. Acid Rain

15. Dissolution Several common minerals dissolve in water
halite
calcite
Limestone and marble contain calcite and are soluble in acidic water
Marble tombstones and carvings are particularly susceptible to chemical weathering by dissolution.

16. More Dissolution Caves and caverns typically form in limestone
speleothems - cave formations; made of calcite
form a rock called travertine
stalactites - from ceiling
stalagmites - on ground

17. More Dissolution
Karst topography forms on limestone terrain and is characterized by:
caves/caverns,
sinkholes,
disappearing streams,
springs

18. Acid Leaching

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

20. Hydrolysis – affected by H20
Feldspar alters to clay
Feldspars = stable at high temperatures and pressures
Clays are stable under conditions at the Earth's surface
Quartz turns to sand

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

23. Spheroidal Weathering
chemical weathering of jointed rocks.
weather to form spherical shapes

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

25. 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

26. 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?

27. Erosion Movement / transportation
Wind, water, glacier
Mast Wasting - Movement of large amounts of material downhill under gravity
Creep
Mudflows
Slump
Rockfalls
Landfalls
Avalanches

29. What happens to Granite?
Granite contains Na Plagioclase feldspar, K feldspar, Quartz
Lesser amounts of biotite, amphibole, or muscovite
Weathering
1. The feldspars undergo hydrolysis to form ________ and Na and K ions The Na and K ions removed by leaching.
2. The biotite & amphibole will undergo hydrolysis to form clay, and oxidation to form _________.
3. The quartz (and muscovite, if present) will remain as residual minerals because they are very resistant to weathering. They get smaller to make ________.
Weathered rock fragments are one of the constituents of soil – our next topic.