Weathering, Soil, and Erosion

• How do rocks go from rocks to sand, etc.?

  By physical and chemical weathering
• Weathering v Erosion

  Weathering is the mechanical and chemical alteration(breakdown) of earth materials at or near the surface. Erosion involves removing weathered materials from their place of origin.
• What controls rate of weathering?

  Parent material (minerals and structure)

  Climate (rainfall and temperature)

  Presence or absence of soils

  Length of exposure time

  Plants and animals

  Slope
• Rocks are not compositionally and structurally homogenous
• Differential weathering

  Different parts of a rock will weather at different rates
• What are some products of weathering?

  Soluble salts

  Ions in solution

  Solid particles
• Frost Action - Physical weathering

  Water freezes in cracks on rocks, expanding it. It contracts when it thaws, thus exerting pressure and opening cracks wider.

  Results in angular pieces (may tumble and accumulate)
• PRESSURE RELEASE AND SHEET JOINTS

  Fracture more/less parallel to exposed rock surfaces

  Enchanted Rock in Central Texas
• THERMAL EXPANSION AND CONTRACTION

  Extreme heating and cooling in deserts, or forest fires can crack rocks

  Dark minerals absorb heat better
• ORGANISMS


  Any organic activity such as tree roots growing in cracks
• minerals in rocks are chemically altered during chemical weathering.
• Chemical weathering is accelerated by hot and wet environment
• Chemical weathering occurs in all environments except permanently frozen polar regions.
• What are the chemical processes?

  Dissolution

  Oxidation

  Hydrolysis
• Chemical stability


  Resistance of a mineral to change
• What is solubility?

  The amount of minerals dissolved in water to reach saturation.
• What is dissolution rate?

  Amount of mineral that dissolves over a given length of time.
• What factor control the rate of chemical weathering?

  Stability of igneous minerals during chemical weathering is inverse of Bowen’s reaction.
• What is dissolution?

  Dissolution of carbonate rocks. The atoms making up the minerals separate and rock dissolves.
• What is oxidation?

  Rocks rust.

  Rocks such as sandstone may contain mineral that will break down when exposed to oxygen. An example would be the Double Arch in Arches Natural PArk in Utah.
• What is hydrolysis?

  K-feldspar

  Hydrogen ions react with and replace positive ions in K-feldspar.
• Chemical weathering is the process by which rocks are broken down through chemical reactions, resulting in a change in their composition.
• Hydration is a type of chemical weathering that occurs when rocks absorb water, causing them to expand and crack.
• Oxidation is a type of chemical weathering that occurs when rocks react with oxygen, causing them to rust or change color.
• Abrasion is a type of physical weathering that occurs when rocks are worn down by friction and rubbing against each other.
• Biological weathering is the breakdown of rocks caused by living organisms, such as plants and animals, through processes like root growth and burrowing.
• surface area

  surface area exposed; the faster the weathering
• what is spheroidal weathering?

  Weathering process that causes rocks to become rounded or spheroidal in shape.
• What are regolith?

  layer of weathering products on earth’s surface
• What makes up soil?

  45% mineral particles

  25% air

  25% water

  5% organic matter (4% humus; 0.5% roots; 0.5% organism)
• soil horizons forms from soil formation. They differ from one another in texture, structure, composition, and color.
• How is regolith made in moon?


  meteorite impact
• How is regolith made in mars?

  Meteorite impacts, volcanic activity, and weathering (wind, ice, water).
• How is regolith made on earth?

  meteorite, plate tectonics, wind, ice, water, plants, animals, humans.
• What factors control soil formation?

  Climate, parent material, organisms, topography, and time.
• Climate is the most important factor in soil formation because chemical processes operate faster where it is warm and wet.
• Forest soils develop in humid climates such as the eastern United States and much of Canada. Humid forest have lots of organic matter.
• Hot deserts

  Little to no organic material

  irregular masses of calcite found under zone of leaching

  Desert soils are often alkaline
• What are laterites?

  Red tropical soils

  Severe, long-lasting chemical weathering.
• What is soil degradation?

  Any process that leads to loss in soil fertility, including erosion, contamination with pollutants, and destruction of soils’ nutrients.