Weathering, Erosion, and Soil

Chapter 7 Notes

  1. Mechanical weathering: ______
  2. Chemical weathering: ______
  3. Frost wedging: ______

Chapter 7.1 – Weathering - (See your chapter 6 notes for definitions of weathering and erosion)

  • Weathering and erosion are both ______processes, because they make parent material, or rock, smaller.
  • There are two types of weathering: mechanical and chemical

Mechanical Weathering / Chemical Weathering
______breaking down rock / ______reactions change the composition of the rock
______change the rock’s composition / Results in the formation of ______and release of ______
Changes the ______and ______of the rock / Changes the ______, ______, and ______of the rock
Examples include: ______/ Examples include: ______

Ways to get Mechanical Weathering:

  • Temperature
  • Can cause ______
  • As water freezes it ______
  • As it expands, it pushes on the edges of the crack it is in, ______
  • When the water thaws, it can ______
  • When it freezes again, the process repeats
  • Eventually, the rock can be broken into pieces from these cracks
  • Pressure
  • When overlying rock layers are removed from a rock, the pressure on the bedrock below is ______
  • The bedrock surface is then able to ______and long, curved cracks can form or existing cracks can become larger
  • Pressure can also be exerted when plants or trees grow in the cracks of rocks
  • As the roots grow larger, they put pressure on the sides of the crack, making them widen

Chemical Weathering

  • ______is the main agent
  • Hydrolysis
  • To some extent, the ______of rocks determines the effects that chemical weathering will have on them
  • Temperature also affects chemical weathering as it influences the ______
  • Different gases can also react with elements in a sample:
  • Oxidation  reaction of oxygen with other substances, usually metals
  • Most common form is rust, or iron oxide
  • Carbon dioxide
  • Can create weak carbonic acid if it combines with water vapor in the atmosphere, which can then fall to Earth’s surface as acid rain (and do chemical weathering)
  • Sulfur dioxide and Nitrogen
  • Can create sulfuric and nitric acids in the atmosphere, which then fall as acid rain

Rates of Weathering

  • Climate
  • Has major effects on the rate of weathering based on ______, ______, and ______in an area.
  • Rock Type and Composition
  • The characteristics of a rock, including how ______or ______they are to being broken down, depend on their ______and ______
  • Surface Area
  • The ______the total surface area, the ______weathering that occurs
  • Topography and other variables
  • Topography  ______
  • Materials that are on a level field are likely to remain in place as they undergo changes, whereas materials on a slope are more likely to move down the slope
  • As material move down a slope, it exposes underlying surfaces and therefore provides more opportunities for weathering to occur

Chapter 7 Questions:

  1. How does mechanical weathering promote chemical weathering?
  2. In what areas does chemical weathering occur the fastest? Why?
  3. Heat speeds up most chemical reactions. Why then does chemical weathering happen slowly in a hot desert? (Hint: think about what the most important agent of chemical weathering is)
  4. What rock type is most easily weathered? Why?
  5. Is erosion purely a destructive force, or does it have constructive aspects as well? Explain your answer and give examples. (Hint: read p. 163-166)