1. LEARNING OBJECTIVES:
Summarize the difference between mechanical and chemical weathering.
Identify the factors that affect the rate of weathering.

2. UNIT 5 WEATHERING, AND WATER
1. Weathering-the chemical & physical breakdown of rock exposed to air, moisture, & living organisms.

3. 2. Regolith-loose layer of fregments that covers much of Earth’s surface.
3. Soil-uppermost layer of regolith, which can support rooted plants.
The rock in the photo
has weathered in place
with little erosion, forming
soil.

5. 4. Mechanical weathering- breakdown of rock into solid fragments by physical processes.
Chemical composition of rock not altered.
Frost wedging.

6. a. Frost wedging-cracking of rock mass by expansion of water as it freezes in crevices & cracks.

7. b. Thermal expansion and contraction-repeated heating & cooling of materials causes ridid substances to crack & separate.

8. c. Joints-fracture of rock, along which no appreciable movement has occurred.
Ex. Sheet jointing or exfloiation.

9. b. Abrasion-gradual wearing down of bedrock by constant battering of loose particles transported by wind, water or ice.
The jointing in these rocks has exposed new surface
area which has broken and smoothed due to wind
water & ice.

10. Ex. Wind abrasion
Ex wind and water abrasion

11. 5. Chemical weathering- decomposition of rocks & minerals by chemical & biochemical reactions.
Plant wedging

12. a. Dissolution-separation of materials into ions in a solution by a solvent, such as water or acid. Rainwater acts as a weak solution of carbonic acid , and acid rain from air pollution.
Marble grave
marker has been
attacked by acidic rain
because of calcite
composition. The
grave marker on the
right, while old, has not been dissolved because of its granite composition.

14. 6. Factors affecting weathering.
a. Tectonic setting: young, rising mountains weather relatively rapidly
Mechanical weathering
most common.

15. b. Rock composition: minerals weather at different rates.
c. Topography
& rock structure
Weathering
occurs faster on
steeper slopes.

16. d. Climate: Chemical weathering more prevalent in warm, wet tropical climates.
Mechanical weathering more prevalent in cold relatively dry regions

17. e. Vegetation promotes weathering due to increased water retention
e. Vegetation promotes weathering due to increased water retention. Removal increases soil loss.
Weathering both mechanical & chemical.
Biological activity

18. distances. 7. Erosion & Mass Wasting
Erosion-removal of weathering products from source & most often occurs by water.
a. Wind: particles of sand transported close to the surface.
Finer particles of
silt & clay can be
transported great
distances. F
Silt

19. b. Glacier-frozen body of ice that mover under the weight of the ice
b. Glacier-frozen body of ice that mover under the weight of the ice. Glaciers remove, breaks & transports rock pieces, scour valleys & deposits piles of
debris as
Moraines.

20. Glacial till
Striated & polished rock

22. Mass wasting- downslope movement of regolith/bedrock masses due to gravity.
Slope failure-falling or sliding of relatively coherent masses of rock.

23. Landslide