1. Weathering & Erosion

2. Weathering and Erosion
Weathering is the break down of rocks that have been exposed to the atmosphere
Once the rocks are broken down, the pieces are transported from one place to another. This process is called erosion
Erosion is caused by wind, moving water (streams, waves, ocean currents), ice (glaciers), and by gravity.
*Most erosion that takes place on Earth is caused by moving water

3. Types of Weathering
  Mechanical weathering – rocks are broken down into smaller pieces without changing their composition (doesn’t change what they’re made of)
Chemical weathering - rocks break down as their minerals change in composition (they become different substances)

4. Types of Mechanical Weathering
Ice wedging/frost action
water enters small cracks in the rock
When it freezes, it expands and forces the crack to open more
The process repeats over again until the rock breaks apart

6. Eventually, the rock splits from repeated frost action!

7. Types of Mechanical Weathering
Wetting and drying
breaks up rocks that are made from clay
When they are wet they expand, and they shrink as they dry
As this repeats over and over, the clay becomes weak and cracks (think of all the projects you have made out of clay…they all crack and fall apart)!

10. Types of Mechanical Weathering
Exfoliation
soil and rock is removed (glaciers or uplifting), exposing rock found deep underground
This releases the pressure causing the surface of the rock to expand and eventually crack

14. Types of Mechanical Weathering
Plant Roots
The deep roots of trees often break apart rocks
Lichen & Moss
These low to the ground plants can grow on rocks and eventually break them apart

16. Types of Chemical Weathering
Hydrolysis
water (hydro) reacts with minerals such as feldspar and form clay

18. Types of Chemical Weathering
Oxidation
oxygen reacts with some minerals, especially those containing iron (magnetite) to form rust (called iron oxide)
This occurs faster with water!

19. Chemical weathering of basalt

20. Iron Banding in Basalt

21. Oxidative weathering of mineral deposits (new deposits are white/yellow, weathered deposits are reddish-brown)

22. Types of Chemical Weathering
Carbonic acid
carbon dioxide (CO²) dissolves in water to form this acid
can cause minerals to dissolve, especially those containing calcite

23. “Gnarled Rock” – a formation of limestone chemically weathered by acid rain

25. Factors which affect rates of weathering:
Rock’s resistance to weathering (HARDNESS)
Amount of surface area
Climate:
Chemical weathering occurs faster in warm, wet climates
Mechanical weathering occurs faster in cold or dry climates

26. The central area of rock was less resistant to weathering…thus the “arch” was formed!

28. Surface Area Greater surface area increases the rate of weathering
Surface area is the amount of rock surfaces exposed to the atmosphere
Weathering creates more surface area

30. Dry Climate = Mechanical Weathering!
Devil’s Marbles, Australia – Mechanical weathering from wind and sand!

31. Warm Climate = Chemical Weathering
Parthenon – Athens, Greece