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Weathering and Soils

Unit 2- Minerals, Rocks, Soils and Weathering. Weathering and Soils. Weathering. Breaking down of rocks and other materials on the Earth’s surface it is a slow, continuous process effects aren’t easily observed Two Types:

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Weathering and Soils

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  1. Unit 2- Minerals, Rocks, Soils and Weathering Weathering and Soils

  2. Weathering • Breaking down of rocks and other materials on the Earth’s surface • it is a slow, continuous process • effects aren’t easily observed • Two Types: • Mechanical: rocks are broken into smaller pieces but their chemical makeup does not change • Chemical: chemical makeup of rocks is changed as rocks are broken down

  3. Mechanical Weathering • What causes Mechanical Weathering? • Temperature: • Rocks expand/contract (cycle) • Causes exfoliation (flaking) • Ice-wedging: • Water seeps into small cracks, freezes and expands, which enlarges cracks. (cracks in sidewalk, potholes in road) • Organic Activity: (caused by living things) • Plant roots can loosen rock, make cracks larger (grass in sidewalk)called root-pry • Abrasion: wearing away of rocks by particles carried by wind, water, etc. • Rough edges of particles ‘scrape’ off parts of rocks. Rocks in a riverbed are scraped by moving objects in the waterthey become smooth

  4. Ice-wedging Plants and Animals As trees grow, their roots expand and have the force to split apart rocks. Animals that burrow in soil or rock expose fresh surfaces to weathering.

  5. Abrasion Sand particles lifted free of the surface can "sand blast" rock surfaces. Gravity Rocks in a riverbed are scraped by moving objects .

  6. Exfoliation The rocks peel like an “onion”, due to expanding and contracting of heat and cold or by pressure release.

  7. Chemical Weathering • What causes Chemical Weathering? • Water • Dissolves minerals that hold rocks together (hydrolysis) • Forms acids when mixed with gases in atmosphere (Acid precipitation) • Acid precipitation has a ph of less than 5.6 • Combines with mineral to make new mineral (combine w/ feldspar to make clay) • Oxidation • Oxygen chemically reacts with something else such as the iron in rocks. (Iron + Oxygen = rust) Inner rock will be different color than outer rock.

  8. Chemical Weathering, cont. • Carbonation • Carbon dioxide and water form a weak acid. It dissolves certain rocks (limestone) but not strong enough to harm plants/animals (Caverns are created this way) • Sulfuric Acid • caused by pollutants-they dissolve in rain to form acid rain. It corrodes (wears away) rocks, metals, etc. quickly. • What do you think it does to monuments and buildings? • Plant Acids • Plants produce weak acids that dissolve certain minerals (mosses and lichens) and break rocks into smaller pieces.

  9. Acid Rain Oxidation Plant Acids Carbonation

  10. Climate and Chemical Weathering

  11. There is a higher rate of mechanical and chemical weathering in Asheville than in Phoenix.

  12. What affects the rate of Weathering? • Surface area • When rock is in small pieces, more surface area is available for weathering • Topography, other variables • Materials on slopes are more likely to move due to gravity. • This exposes underlying rock, providing more opportunities for weathering.

  13. Temperature The rate of chemical weathering occurs faster in warm, humid climates. Oxidation occurs at a faster rate when temperatures are high and H20 is present. Mailbox-dry climate Mailbox-warm, humid climate

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