1. Weathering: Processes of Change
chemical weathering
mechanical weathering
moving water
erosion
ice
deposition
waves
gravity
wind
glaciers
Acids
abrasion

2. How does weathering occur?
EQ:
How does weathering
occur?

3. Weathering Describe three ways abrasion occurs in nature.
List three things that cause chemical weathering of rocks.
Describe the similarity in the ways tree roots and ice mechanically weather rock.
Describe five (5) sources of chemical weathering.

4. The Processes of Change
Lesson 18

5. Processes of Change (5)
Weathering and erosion wear down, deposition fills in Earth’s surface.
Weathering is the slow wearing away or breaking down of objects exposed to Earth’s atmosphere
Two kinds of weathering act on Earth’s surface
Mechanical weathering
Chemical weathering

6. Weathering
Weathering is the process by which rock materials are broken down by the action of physical or chemical processes.
Mechanical weathering is the breakdown of rock into smaller pieces by physical means. (ice, wind, water, gravity, plants, animals)
Chemical weathering is the process by which rocks break down as a result of chemical reactions. Water, weak acids, and air can cause chemical weathering.

7. Mechanical Weathering (4)
When objects are broken down into small pieces but their chemical makeup doesn’t change
Wind and moving water are two main causes of mechanical weathering
Repeated changes in temperature (freeze, melt, freeze, melt again)

8. Chemical Weathering (5)
Material of an object is changed
Produces underground caverns
Statue of Liberty needed repairs because of chemical weathering
Examples:
Rust
Acid rain

9. Erosion (5) The natural moving of material from one place to another
Erosion transports weathered rock material
Causes of Erosion:
Moving water
Gravity
Wind
Glaciers (moving rivers of ice)
Waves

10. Deposition (5)
Land torn down in one place is “deposited” in another place
Gravity can cause a landslide moving mud, rock and soil down a hill
Wind erosion can move sand and deposit it in another area
Glaciers (rivers of ice) scrape rocks off the land and moves them downhill

11. Glaciers will stop moving and even retreat and cut a steep U-shaped valley in the land

12. Erosion caused by mountain rivers form V-shaped valleys

13. Hurricanes create waves that erode beaches and cliffs

14. Breaking of waves on a beach can wear it away
Breaking of waves on a beach can wear it away. The larger the waves, the faster is the rate of erosion.

15. 6 Agents of Mechanical Weathering
1. Ice – water seeps into cracks during warm weather. When the temperature drops, the water freezes and expands, causing the ice to push against the sides of the crack. This causes the crack in the rock to widen.
Abrasion – the grinding and wearing away of rock surfaces through mechanical action of other rock or sand pebbles.
The three ways that can cause abrasion are wind, water, and gravity.

16. Abrasion
Abrasion – the grinding and wearing away of rock surfaces through mechanical action of other rock or sand pebbles.
The three ways that can cause abrasion are wind, water, and gravity.

17. Three Causes of Abrasion
2. Water – as rocks and pebbles roll along the bottom of flowing water, they bump and scrape against each other, causing these rocks to become rounded and smooth.
3. Wind – wind blows sand and silt against exposed rock eventually wearing away the rock’s surface.
4. Gravity – rocks grind against each other during a rock slide, creating smaller and smaller rock fragments. Anytime one rock hits another rock, abrasion takes place.

18. Plants and Animals
5. Some plants can easily break rocks. The roots grow through existing cracks in rocks. The growth causes the root to expand, forcing the crack to widen. The force can eventually split the rock apart.
6. Animals that live in the soil (moles, prairie dogs, insects, worms, gophers), cause a lot of weathering. By burrowing in the ground, these living creatures brake up soil and loosen rocks to be exposed to further weathering.

19. 3 Agents of Chemical Weathering
Common agents of chemical weathering are water, weak acids, and air.
These agents weaken the bonds between minerals grains of the rock.
1. Water – can cause rock to be broken down and dissolve. Can take thousands of years to take place.
2. Air – the process of oxidation is a chemical reaction in which an element (iron) combines with oxygen, causing rust.
3. Weak Acids - acid precipitation, acids in groundwater, acids in living things.

20. Three Sources of Weak Acids
Acid Precipitation – rain, sleet, or snow that contains a high concentration of acid. Normal precipitation is acidic, acid precipitation contains more acid than normal.
Acids in Groundwater – carbonic acid or sulfuric acid reacts with rocks in the ground, causing a chemical reaction, eating away at the rock.
Acids in Living Things – Lichens produce acids that slowly break down rock.

21. Summary
Ice wedging is a form of mechanical weathering in which water seeps into rock cracks and then freezes and expands.
Wind, water, and gravity cause mechanical weathering by abrasion.
Animals and plants cause mechanical weathering by turning the soil and breaking apart rocks.
Water, acids, and air chemically weather rock by weakening the bonds between mineral grains of the rock.

22. Quick Check
Which of the following things cannot cause mechanical weathering?
A. water
B. acid
C. wind
D. animals

23. Quick Check Which of the following is a type of frost action?
A. abrasion
B. oxidation
C. ice wedging
D. gravity

24. Quick Check
Which of the following types of chemical weathering causes a karst landscape, such as a cavern?
A. lichens
B. acid precipitation
C. acids in groundwater
D. water

25. Quick Check How do lichens slowly break down a rock? A. by abrasion
B. by mechanical means
C. by ice wedging
D. by chemical means

26. Quick Check
Which of the following will most likely experience oxidation?
A. tennis ball
B. aluminum can
C. wooden fence
D. Bicycle tire

27. Quick Check
The grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles
Rain, sleet, or snow that contains a high concentration of acids
The process by which rocks break down as a result of chemical reactions
The breakdown of rock into smaller pieces by physical means
A chemical reaction in which an element, such as iron, combines with oxygen to form an oxide
The process by which rock materials are broken down by the action of physical or chemical processes
a. mechanical weathering
b. oxidation
c. weathering
d. acid precipitation
e. abrasion
f. chemical weathering