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Weathering, soils, & erosion
- 1. Weathering, Soils, &Erosion Earth Science Unit 7 (Chapter 14)
- 2. What is Soil •Soil is a complex mixture of weathered rock, minerals, organic material (both living & decaying), water, and air. • Different soils have different amounts. • What might change the amounts? • On average, soil has the following ratios: – 45% minerals & rocks – 25% water – 25% air – 5% organic material
- 3. How is SoilProduced? • Weathering of rocks and minerals • Deposits of sediments washed/blown to the site • Decomposition/actions of living things.
- 4. Weathering of Rock •Weathering is the physical or chemical breakdown of rock into smaller pieces • These pieces may be large or too small to see! • Two types of weathering: – Mechanical – Chemical
- 5. Mechanical Weathering • Physicalbreakdown of rock • Chemical composition of the rock does not change • Types: – Exfoliation – Ice Wedging – Abrasion – Plant & Animal Activity
- 6. Exfoliation • When rockscome to the surface, pressure on them is reduced. • This can allow cracks to form, and the rocks break apart. • Example: Granite
- 7. Ice Wedging • Whenwater flows into the cracks in rocks & freezes. • Why does this split the rocks?
- 8. Abrasion • When rocksbroken from other processes collide and break even more. • Happens because of gravity, ice, running water, or wind…wait, how does wind do this?
- 9. Plant & AnimalActivity • Plant roots act like ice to split rocks • Animals, mostly ones that burrow, expose other rocks for further weathering.
- 10. Chemical Weathering • Chemicalreactions break the minerals in the rock into different materials • Types: – Oxidation – Hydrolysis – Carbonation – Organic Acids – Acid Rain
- 11. Oxidation • When elements in the rock combine with Oxygen, and break off as new compounds. • Usually happens in rocks with iron • Produces a red color
- 12. Hydrolysis • When chemicalsin the rock react with water, causing some of the minerals to break away from the rock. • Often happens with metals like Potassium & Aluminum
- 13. Carbonation • When CO2gets into water it makes Carbonic Acid • This acid can stick to some minerals and form compounds that are washed away by water. • This often happens to limestone.
- 14. Organic Acids • Someliving things produce acids that are released to the environment. • These acids can make cracks in rocks and start the weathering process. • Examples: Lichens & mosses
- 15. Acid Rain • Nitrogen& Phosphorus from fossil fuels get into the air and combine with rainwater • This rainwater weathers rock more rapidly than normal rain.
- 17. Quick Quiz #1 •Why would rocks high in the mountains weather more quickly than rocks in a plain? • You have 10 lbs. of rocks. 5 lbs. are in two rocks, and the other 5 lbs. are in 10 rocks. Which 5lb. Pile will weather more quickly? • A stone statue in the desert will weather more ______________than a stone statue in PA. • This happens when the softer areas of rock weather away before the harder areas or rock.
- 18. Formation of Soil •When new rock is exposed, soil begins to form. • This newly exposed rock is known as Bedrock.
- 19. Formation of Soil •Weathering begins to break the bedrock into smaller rocks. • This layer of partially weathered rocks, above the bedrock, is known as Regolith.
- 20. Formation of Soil •The top of the Regolith is weathered even more, producing small particles that begin to form soil. • Sediments from water or wind may add to the soil. • Also, organic material begins to add to the soil.
- 21. Formation of Soil Immature soil Regolith Bedrock Young soil Mature soil
- 22. Soil Characteristics • Themain characteristics of a soil are determined by the bedrock it formed from…this is the Parent Material. • Parent material can affect soil texture and soil color. • Example: quartz-rich rocks produce sandy soil. • Example: iron-rich rocks produce red soil.
- 24. Soil Characteristics • Thesize of soil particles also affects the characteristics of a soil. • Soils are usually categorized by the amounts of each type of particle that they have. • Particles are: – Clay: less than 0.0002mm – Silt: 0.0002mm – 0.05mm – Sand: 0.05mm – 2mm
- 27. Effects of ParticleSizes • The size of soil particles affects how much water & air the soil can hold. • The smaller the particles, the less the soil can hold. • However, if the soil is made entirely of larger particles, the water will run right through the soil! • We measure particle sizes by measuring Porosity.
- 28. Porosity: The measure of thevolume of pores and distance of pores per volume of soil
- 29. Effects of ParticleSizes • Infiltration: the rate at which water from precipitation or other sources flows into the soil
- 30. Saturation The amount ofwater and air that can move through soil Water Water High permeability Low permeability
- 32. Soil Profiles • Theformation of soil in different areas produces different layers. • These layers are called Horizons. • The composition and depth of horizons is measured by looking at a Soil Profile.
- 33. Soil Horizons Immature soil O horizon Leaf litter A horizon Topsoil B horizon Regolith Subsoil C horizon Young soil Parent material Mature soil
- 34. Soil Horizons • OHorizon: • Top Layer/Surface litter layer • Mostly plant debris (leaves, branches) and animal waste • Brown/black in color
- 35. Soil Horizons • AHorizon • The Topsoil Layer • A mixture of decomposing organic matter called Humus • And… • Small soil particles from the bedrock • Contains most plant roots and soil organisms.
- 36. Soil Horizons • BHorizon (Subsoil Layer) • A transitional layer of parent material, organic material, and minerals leeched from the A horizon. • Leaching is when water reacts with minerals in the upper soil layers, carrying them to the B horizon.
- 38. Soil Horizons • CHorizon (parent material): • This is the regolith…which is…? • The partially weathered rocks from the bedrock. • This layer usually has no organic material. • Below the C horizon is the bedrock.
- 39. Typical Pennsylvania SoilProfile
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- 41. Different Soil Profilesin Rice Fields
- 42. What changes aSoil Profile? • What determines the composition of a soil? • Mostly the bedrock, erosion, & organic stuff…but what determines these?!? • Climate! • Climate mostly affects the layers of a soil, but not the materials found in the soil. • In general, climates that have all 4 seasons have all the layers of soil.
- 43. Soil Layers &Climate
- 44. Tropical Rainforest Soils •Large amounts of rain leech minerals from the upper layers to the B horizon, which becomes very thick. • Almost no mechanical weathering…why? • Decomposition is high…why? • Would this be good for farming?
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- 46. Desert/Arctic Soils • Verylittle rainfall, so almost no chemical weathering. • Little life, so not much organic material. • Soil is mostly regolith (C horizon) with a little organic material at the top (O horizon)
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- 48. Temperate Soils • Thisis where we live. • Varying seasons provide all kinds of weathering. • Lots of life, so there’s lots of organic material. • Soils in these areas usually have all 4 layers.
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- 51. Soil Erosion • Whatis erosion? • The movement of weathered materials from one location to another. • So…isn’t this the same as weathering? • No! Weathering helps to build soil, soil erosion destroys soil.
- 52. What Causes SoilErosion? • Wind • Gravity • Water • Glaciers • Human Actions can speed up the process!
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- 61. Humans & Erosion •So, how do humans affect this Soil Erosion thing? • Development for housing/buildings • Farming…this is the big one
- 62. Humans & Erosion •Farming can expose a lot of lose soil to erosion. • This soil is the O and A horizons…why are these important? • These contain most of the organic material in the soil, which plants and animals need to survive.
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- 64. Is Erosion Reallya Problem? Areas of serious concern Areas of some concern Stable or nonvegetative areas
- 65. What can wedo to prevent Erosion?
- 66. Contour Plowing • Hillsidesare plowed in curves that follow the shape of the land. • Prevents water from flowing straight down.
- 67. Strip Cropping • Cropsare planted in alternating bands. • This way, the whole area is not filled with row crops that don’t cover all the land.
- 68. Terracing • Hills arecarved into flat “steps”. • This prevents water from flowing rapidly down the hill.
- 69. Crop Rotation • Plantinga crop to harvest 1 year, and one to leave in place the next year. • Often combined with strip and contour farming.
- 70. Quick Quiz #2 •In your experiments, the variable you measured is known as the _______________ variable. • This region would have a large B horizon in the soil, full of minerals leeched from the upper layers. • These soil particles are the smallest. • The measure of the rate of water movement into the soil.