1. Weathering

2. Weathering
The process by which rock materials are broken down by physical or chemical processes
2 types of weathering
Mechanical weathering
Chemical weathering

3. Mechanical Weathering
The breakdown of rocks into smaller pieces by physical means
Mechanical weathering can occur due to:
Ice
Abrasion
Water
Wind
Gravity
Plants
Animals

4. Mechanical Weathering: Ice
Frost Action: The freezing and thawing of soil and rock
Ice wedging is a type of frost action
Water seeps into cracks during warm weather
When temperatures drop, the water freezes and expands
The ice pushes against the sides of the crack causing the crack to widen

5. Ice Wedging

6. Mechanical Weathering: Abrasion
Abrasion: the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles

7. Mechanical Weathering: 3 Forms of Abrasion
Water – Rocks in rivers bump and scrape each other as they are carried by the water, causing them to become smooth and rounded
Wind – Wind blows sand against rock causing wearing away the rock’s surface
Gravity – As rocks fall on one another, they crack, scrape and break into smaller pieces

8. Water Abrasion

9. Wind Abrasion

10. Gravity Abrasion

11. Mechanical Weathering: Plants & Animals
As a plant grows, the force of the expanding root becomes so strong that it can break a rock apart
Animals
Almost any animal that burrows causes mechanical weathering by mixing and digging through soil and rock particles

12. Plants

13. Animals

14. The Shape of Rocks
Weathering takes place on the outer surface of rocks
The more surface area that is exposed to weathering, the faster the rock will be worn down
Smaller rocks have more surface area and therefore weather more quickly

15. Chemical Weathering
The process by which rocks break down as a result of chemical reactions
Chemical weathering can occur due to
Water
Acid
Air

16. Chemical Weathering: Water
Water chemically reacts with the minerals in a rock, causing those minerals to become soft and breakdown

17. Chemical Weathering: Acid
Acid Rain: rain, sleet, or snow that contains abnormally high concentrations of acids
Air pollution, from the burning of coal and oil, combines with water in the atmosphere and falls to earth as acid rain
The acid in the rain corrodes or chemically destroys the rock
Acids in Groundwater
Acidic groundwater chemically reacts with rocks in the ground, such as limestone
This chemical reaction dissolves the limestone, creating caverns
Acids in Living Things
Some living things, such as lichens, produce acids that can slowly break down rocks

18. Acid Rain

19. Acid Groundwater

20. Acid Organisms

21. Chemical Weathering: Air
Oxidation: the chemical reaction where iron combines with oxygen in the air to form rust

22. Rates of Weathering
Weathering takes a long time but some rocks with weather faster than other rocks
3 Factors affect the rate of weathering:
Makeup of the rock
Climate
Elevation

23. Differential Weathering
The process by which softer, less weather resistant rocks wear away and leave harder, more weather resistant rocks behind
Devils Tower was once deep inside an active volcano
After thousands of years of weathering, the soft outer parts of the volcano have worn away
The harder, more resistant rock is all that remains

24. Differential Weathering

25. Weathering & Climate
Climate is the average weather condition in an area over a long period of time
The rate of chemical weathering is faster in warm, humid climates
Oxidation happens faster when temperatures are high and water is present

26. Weathering & Elevation
Rocks at higher elevations, like on a mountain, are exposed to more wind, rain, and ice which causes them to weather faster
Gravity pulls things, like water and rocks, down faster
Water carries rocks down the mountain
Rocks fall from the sides of the mountain