1. Weathering and Erosion
Earth Processes
Hill Science 6

2. Weathering
Weathering is the wearing or breaking of rocks into smaller pieces by water, temperature changes, wind, living things, or chemical changes.
The fragments of rock stay in place.

3. Weathering There are two types of weathering: Mechanical weathering
and
Chemical weathering

4. Mechanical Weathering
The physical breakdown of rocks into smaller pieces, gradually reducing them to the tiny particles that make up soil.

5. Agents of Mechanical Weathering
Wind, water, gravity, glaciers - Abrasion
Ice – ice wedging
Pressure change – inside earth to surface of earth - exfoliation
Temperature change – alternating hot to cold - exfoliation
Plants and animals – organic activity – root pry, animal burrowing

6. Arches National Park, Utah, USA
Wind
Arches National Park, Utah, USA

7. Type of Weathering? WIND ABRASION
These rocks have been blasted by wind and sand causing them to become rounded.
Type of Weathering?
WIND ABRASION

8. Water
The Grand Canyon created by the Colorado River

9. Water
Friction and Repeated Impact
Type of weathering?
Abrasion

10. Glacial Action
Glacial ice will scour and abrade the surface it slowly scraps over. Glaciers form broad U-shaped valleys in their wake.
What type of weathering?
Abrasion

11. Exfoliation
On Half Dome, the rock is peeling away from the mountain in layers just like an onion. This is called exfoliation which is caused by the change in pressure when a rock that was formed underground is thrust to the surface.

12. Pressure Changes What type of weathering? Exfoliation
Peeling of the surface of a rock due to pressure change.
What type of weathering?
Exfoliation

13. Temperature Changes Warm to cold and back again
Splits rocks or peels off layers

14. Temperature Change What type of weathering? Exfoliation
Repetition of cooling and heating over and over again. When might that happen?
What type of weathering?
Exfoliation

15. Temperature Changes
Water to Ice
Ice Wedging
Heaving
Glaciers

16. Ice Wedging
Water fills a crack, freezes and expands making a larger crack. This process repeats over and over.

17. Ice wedging slowly breaks up this sedimentary rock into unusual shapes.

18. Frost Heaving
Repetitious freezing and thawing of water under the patio causes the surface to heave when the ice expands under the patio and contracts when ice melts.

19. Organic Activity
Plants
What do you see happening here?
Root Pry

20. Plant Roots The action of plant roots is called
root pry

21. Animal Activity- how does this cause weathering?

22. Pictures of Mechanical Weathering
Link to pictures
Link to places

23. Mechanical Weathering
1. Abrasion – the wearing away of solid particles; caused by wind, water, glacier ice, and gravity
2. Ice wedging - when water in a crack or hole in a rock freezes it expands making the opening larger. Melting moves it deeper into the opening and the process repeats; Caused by the repeated thawing and freezing of water.

24. Mechanical Weathering
3. Organic activity – people, animals, or plants break up rock by digging or burrowing. Root pry the splitting of rock caused by the expanding root growing deeper.
4. Exfoliation – flaking off of the surface of the rock; caused by change in pressure from inside earth where formed to lower surface pressure or temperature change.
5. Heaving – rocks shift and crack; caused by repeated freezing and thawing

25. Chemical Weathering
Chemical weathering is the breaking down of rocks by changing their chemical composition.

26. Agents of Chemical Weathering
Acid precipitation - carbonation
Acid from plants – humic acids
Oxygen - oxidation

27. Water
Carbonation - Water weathers rock by dissolving it

28. Carbon Dioxide CO2 dissolves in rain water and creates carbonic acid
Carbonic acid easily weathers limestone and marble (CaCO3)
A cave may
result
Type of weathering?
carbonation

29. Chemical Weathering Carbonation Sinkhole Stalactites and Stalagmites
Karst terrain

30. Result of Rainwater Weathering
Type of Weathering?
carbonation

31. Humic Acids Acid from Lichens Weathering Rock

32. Living Organisms
Lichens that grow on rocks produce weak acids that chemically weather rock
Type of weathering?
Humic acids

33. Oxygen
Iron combines with oxygen in the presence of water in a process called oxidation
The product of oxidation is rust

34. Oxygen Caused Chemical Weathering
Type of weathering?
oxidation

35. Chemical Weathering
Carbonation-Acid precipitation - CO2 dissolves in rain water and creates carbonic acid which easily changes the chemical composition of certain rocks (limestone and marble)
Humic Acids – lichens and moss produce acids that break down the minerals found in rocks they are growing on
Oxidation – when oxygen combines with another substance to create an entirely new substance Fe + O produces iron oxide (rust)

36. Weathering and Erosion
 Weathering and erosion are called external processes because they occur at or near Earth’s surface.
Weathering and erosion are part of the rock cycle because they are responsible for transforming solid rock into sediment.
So how do they differ?

37. Weathering or Erosion?
Weathering is the breaking of rocks into smaller pieces.
Erosion is the moving of weathered sediments from one place to another.
Erosion is the transportation of weathered material by the mobile agents of wind, water and glacial action (ice).

38. Video Links Formation of the Grand Canyon Grand Canyon Lava Flows
Ireland: Glaciated Landscape

39. Principal of Uniformity
Belief that the processes that changed our world in the past are still in existence today and continue to change the earth.

40. Chemical Weathering
Chemical weathering is the breaking down of rocks by changing their chemical composition.

41. Differential Weathering
Chapter 10
Rates of Weathering
Differential Weathering
What Is Differential Weathering? Differential weathering is a process by which softer, less weather resistant rock wear away and leave harder, more weather resistant rock. The image below is an example of differential weathering.
Devil’s Tower, Wyoming

42. Rates of Weathering What determines how quickly a rock will weather?
Type of Rock (differential weathering) – some rocks weather more quickly than others, due to composition or condition
Pollution – causes acid precipitation which will weather rocks more quickly
Climate – tropical fastest due to more moisture and plant action, deserts slowest due to lack of humidity
Size – smaller rock has more surface area to volume than a larger rock. More surface is exposed to weathering, so it will weather more quickly.

43. Chapter 10
Rates of Weathering

44. Weathering and Elevation
Chapter 10
Rates of Weathering
Weathering and Elevation
High Elevations Rocks at higher elevations, as on a mountain, are exposed to more wind, rain, and ice than rocks at lower elevations.
Steep Slopes The steepness of mountain slopes increases the effects of mechanical and chemical weathering. Steep slopes cause water and sediments to quickly run down the side of the mountain.

45. Weathering Website Weathering animation click here