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Weathering Erosion and Deposition
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Weathering The breakdown of rock into smaller pieces (Sediment)
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Mechanical Weathering
Rocks broken into sediment by physical means Types Frost heaving and Frost wedging Plant roots Friction and impact Burrowing of animals Temperature changes
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Frost Wedging Expansion of cracks in rock due to freezing ice
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Frost Heaving Wet soil freezes, pushing up the ground above
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Plant Roots
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Friction and Repeated Impact
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Burrowing of Animals
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Temperature Changes
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Chemical Weathering The process that breaks down rock through chemical changes. The agents of chemical weathering Water Oxygen Carbon dioxide Living organisms Acid rain
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Water Water weathers rock by dissolving it
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Oxygen Oxygen makes iron rust. Rust is unstable
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Carbon Dioxide CO2 in soil dissolves in rain water and creates carbonic acid Easily weathers limestone and marble
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Living Organisms Lichens produce weak acids
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Acid Rain Compounds from burning fuels (NOx SO4) form acids in rain.
Very rapid chemical weathering
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Karst Topography A type of landscape in rainy regions where there is limestone near the surface, characterized by caves, sinkholes, and disappearing streams. Created by chemical weathering of limestone
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Features of Karst: Sinkholes
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Features of Karst: Caves
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Features of Karst: Disappearing Streams
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Soil Soil is the product of weathering rocks and dying living things.
Mixture of sediment and organic matter Plants, as well as Fungi, Bacteria, and Invertebrates mix soil over time to form different layers. OM broken down by FBI is called Humus
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Soil Profile A cross section of soil that shows the different layers, called horizons. There are 4 different horizons
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O horizon Top layer 100% organic matter (living or dead)
No sediment, therefore not soil.
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A Horizon The top layer of soil, often referred to as topsoil.
Dark in color because it has lots of organic matter. Also contains roots and animals.
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B Horizon Middle layer of soil
Lighter because it has less organic matter Some plant roots Leeching – water bringing nutrients from one layer into the next
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C Horizon Deepest layer of soil
Contains no Organic matter, only weathered rock. Little to no nutrients.
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Soil Profiles (cont) Soil profiles differ in different areas
Thickness of the various layers depends on the climate type as well as the plant/animal activity above.
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Erosion The process by which water, ice, wind or gravity moves fragments of rock and soil.
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Erosion Factors Rate of Rain Slope of land Plants
More rain More Erosion Slope of land Steeper land More Erosion Plants Fewer Plants More Erosion
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Humans Increase erosion Decrease Erosion Plowing Overgrazing animals
Clear cutting forests Decrease Erosion No-Till farming Contour Farming Terracing Selective cutting of forests
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Water Erosion Rivers, streams, and runoff
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Rills and Gullies Rill and Gully Erosion occur when water moves over steep areas, carving out channels. Rills are formed by small streams. Gullies are formed as rills become broader and deeper due to more water. The fast moving water removes sediment.
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Sheet Erosion Sheet erosion occurs in flat areas where the water slows down. Water flows in wide sheets rather than streams Because the water has less energy, it deposits much of its sediment
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Ice Erosion Glaciers
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Glaciers Valley Glaciers - small glaciers between mountains
Leave U-shaped valley. Continental Glaciers - large glaciers that cover vast areas. Currently cover 10% of earth
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Glacial Erosion Glaciers erode as they move.
They can pick up sediment and move it great distances - Plucking They can also scrape the surface rock resulting in striations
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Glacial Deposition Glaciers drop their sediment (till)as they melt.
Moraines - pile of sediment perpendicular to movement Eskers – winding pile of sediment parallel to movement Drumlin – Streamlined piles of sediment parallel to movement Glacial Erratic - single large rock dropped by glacier
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Wind Erosion
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Wind Erosion Deflation – Wind picks up sediment
Abrasion – Wind carried sediment acts as a sand blaster Loess – fine sediment deposited by slowing wind Dunes – piles of sand constantly moved by wind
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Gravity Erosion (Mass Movements)
Slumps, Creeps, Rockslides and Mudslides
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Slumps Occurs on a steep slope when loose materials slide down the slope in one large mass. Layers under the soil are weakened due to erosion or earthquakes. Leaves curved scar in soil
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Creep Slow mass movement down a less steep slope.
Often caused by repeated thaw melt cycles. Causes tree and fence-posts to lean downhill.
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Landslides & Rockslides
Large areas of rock/soil break loose from a steep slope and move quickly downhill. Occur often after earthquakes or heavy rains. Fan-shaped piles of sediment at the bottom of a slope is good evidence of slides
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Mudflow Occur as mixtures of water and sediment flow down a slope.
Occur after heavy rains in areas of thick dry sediment. Water and sediment forms a thick paste that has lots of momentum, and causes lots of damage.
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