1. Mechanical vs. Chemical Climate and Elevation
Weathering
Mechanical vs. Chemical
Climate and Elevation
for frost wedging, tree roots, and oxidation

2. What is weathering?
Weathering is the process by which rock materials are broken down into smaller pieces.
This can happen by physical processes or chemical processes.

3. Mechanical weathering
Mechanical weathering is the breakdown of rock into smaller pieces by physical means.
Some ways in which mechanical weathering occurs are ice, wind, water, gravity, plants, and animals

4. Ice
Frost action alternates between the freezing and thawing of soil and rock, which weakens rock.
Ice wedging is when water seeps into cracks in rocks during warm weather. When the temperature cools, the water freezes and expands, widening the crack or breaking the rock.
Cracks in the road

5. Ice Weathering

6. Abrasion Grinding and wearing away of rock surfaces
Can happen when rocks and pebbles roll along the bottoms of rivers, causing rocks to become round and smooth.
Can happen when wind blows sand and silt against an exposed rock (sand wears away surface of rock).
Can happen when rocks fall on one another
Where wind, water, and gravity come into play.
Abrasion on skin. Sliding. Turf burn. Floor burn.

7. River rocks are rounded
Rocks grind against each other during rock slide
Rock shaped by blowing sand

8. Plants Plants often send their roots through existing cracks in rocks.
As the plant grows, so does the root, which can widen the crack or split the rock.
Weeds or moss in sidewalk cracks

9. Animals
As animals burrow, they mix up rocks and soil and expose new materials to weathering.

10. Chemical Weathering
Chemical weathering is the process by which rocks break down as a result of chemical reactions caused by water, weak acids, and air.
Example: Letting the Nerds candy dissolve in your mouth

11. Water
Chemical bonds of rocks are broken down by water, much the same way a sugar cube dissolves in water.
This process may take thousands of years

13. Acid
Rain, sleet or snow that contains a high concentration of acids is called acid precipitation.
Can cause rapid weathering of rock.
Acid precipitation is formed by volcanoes and the burning of fossil fuels (coal and oil).

14. Cemetery head stones

15. Acids
Acids can be found in groundwater. These acids react with rocks, such as limestone.
Living things, such as trees, can also contain acids.
Top: Carlsbad Caverns in New Mexico
Bottom: Lichens growing on trees (fungi and algae living together)

16. Air
Oxidation occurs in air when oxygen combines with another chemical.
This process causes rust.

17. Did you know??

18. Weathering and Climate
Climate is the average weather condition in an area over a long period of time.
How can weathering happen quicker?
Chemical weathering happens at a faster rate in warm, humid climates
Wet, cold climates cause mechanical weathering to happen quicker. (i.e. ice wedging)
Climates that have frequent freezing and thawing, increasing the occurrence of mechanical weathering

20. What type of climates do you think these types of weathering are taking place in?

21. Weathering and Elevation
Rocks at higher elevations are exposed to more wind, rain, and ice than rocks at lower elevations. This causes the peaks of mountains and rocks at the peak to weather faster.

22. Weathering Animations
elearning/module07swf.swf