1. 3.1 - Weathering Define mechanical and chemical weathering.
Identify agents of weathering.
Discuss factors that influence weathering.

2. Footprints on the Moon
Footprints left on the Moon from one of the Apollo missions from
Why will these footprints always exist on the moon?

3. What is Weathering?
Process that breaks solid rock into sediments

4. Himalayan Mtns.
Appalachian Mtns

5. 2 Main Types of Weathering
Mechanical Weathering
Chemical Weathering

6. Mechanical Weathering
Breaks rocks down into smaller pieces without changing the chemical composition of the rock
Some Agents of Mechanical Weathering
Ice Wedging
Abrasion
Biological Weathering: Plants and Animals
Human Activities

7. Ice Wedging

8. Abrasion Caused by rocks bumping into each other
Makes rocks with sharp or jagged edges smooth and round
Agents of Abrasion:
Gravity
Moving Water
Wind
Glaciers

9. Moving Water
causes abrasion as particles in the water collide and bump against one another.

10. Wind Strong winds carrying pieces of sand can sandblast surfaces.

11. Glaciers Ice in glaciers carries many bits and pieces of rock.
Rocks embedded at the bottom of the glacier scrape against the rocks below.
The Burren
County Clare, Ireland

12. Biological Weathering: Plants
A plant’s roots can grow into a crack or fracture in rock and gradually grow larger, wedging open the crack.

13. Biological Weathering: Animals

14. Human activities
Human activities are responsible for enormous amounts of mechanical weathering, by digging or blasting intorock to build homes, roads, subways, or to quarry stone.

15. Chemical Weathering
works through chemical reactions that cause changes in the minerals of rock.
Agents of Chemical Weathering
Water (Hydrolysis)
Carbon dioxide (Carbonation)
Oxygen (oxidation)
Acid Rain

16. Water
Hydrolysis = water reacts with compounds in rock causing the compounds to dissolve/break apart
Leaching = occurs as water breaks down compounds in rock and carries ions away
Check out this animation of how water dissolves salt:

17. Carbon Dioxide
Carbon dioxide (CO2) combines with water as raindrops fall through the atmosphere to form carbonic acid.
Carbonic acid dissolves rocks.
Many limestone caves have been formed by the action of carbonic acid.

18. Oxygen
Oxidation is a chemical reaction that takes place when oxygen reacts with another element.
Minerals that are rich in iron break down as the iron oxidizes and forms new compounds.
Iron oxide (rust) produces the red color in soils.

19. Acid Rain
Pollutants, such as sulfur and nitrogen, from fossil fuel burning, create sulfuric acid and nitric acid.
These acids react with water in the atmosphere to form acid rain.

20. Factors that Affect the Rate of Weathering
Exposure to the Atmosphere
Composition of Rock
Climate

21. Exposure to the Atmosphere
Rocks exposed to the atmosphere weather faster than rocks that remain unexposed.
Mechanical weathering can speed up the rate of chemical weathering by increasing the surface area of rock.

22. Composition of Rock Different rock types weather at different rates.
Igneous rocks (especially intrusive) weather slowly because it is hard for water to penetrate them (ex. Granite)
Other types of rock, such as limestone, are easily weathered because they dissolve in weak acids.
Different minerals weather at different rates.
Some minerals dissolve easily in water while others do not.

23. Which type of climate do you think has a higher rate of weathering?
Climate is weather averaged over a long period of time.
Chemical weathering increases as:
Temperature increases:
Chemical reactions proceed more rapidly at higher temperatures.
Precipitation increases:
Since water participates in both mechanical and chemical weathering, more water strongly increases weathering.
Which type of climate do you think has a higher rate of weathering?