Weathering, Erosion and Soil

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WEATHERING, EROSION AND SOIL

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WEATHERING

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MECHANICAL WEATHERING Temperature Freezing temperature causes the expansion of the

molecules of substances - water expands as it freezes

Cracks in concrete, wood, etc. fills with water. Water freezes and expands, causing splitting and breaking apart - frost wedging, ex. pot holes.

Pressure - factor of mechanical weathering. Bedrock at great depth are under pressure as over lying rock is stripped away. The bedrock at depth is exposed. Then the bedrock can expand and cracks will occur.

Exfoliation - stripping of layers of rock - create a dome formation, ex. Stone mountain in Georgia

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EXFOLIATION Stripping of layers of rock Creates a dome formation Ex, Stone Mountain in Georgia Half Dome Yosemite Valley California

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CHEMICAL WEATHERING Rocks change composition as the result

of chemical reactions. Agents - H2O, O2, CO2, and acids. Temperature tends

to speed up and slow down chemical reactions

*Rate of chemical Rx (reactions) doubles with each 10°C increase

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CHEMICAL WEATHERING

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WATER Universal solvent, hydrolysis - reaction of H2O and other

substances Oxygen - oxidation Substance + O2 new substance Fe (Iron) + O2 (Oxygen) Fe2O3 (Rust) Al (Aluminum) + O2 Al2O3 (Aluminum

Oxide) 21% of oxygen is in atmosphere  Minerals - result of oxidation, Ex. Pyrite,

magnetite CO2 - produced through respiration CO2 + H2O H2CO3 (Carbonic Acid, weak acid

form in the atmosphere Carbonic acid reacts with calcite forms

(limestone caverns)  

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ACID PRECIPITATIONAcid Precipitation - Oxidation of sulfur dioxide and nitrogen oxide - that is released by human activitiesSO2 Industrial emissionsNO2 Motor VehiclesSO2 + O2 + H2O Sulfuric acidNO2 + O2 + H2O Nitric acid Acid Rain - PH = less than 5.6Normal Rain - PH = 5.6 Water in lake - 6 to 8 PH Lower PH kill fish To reverse acidificationAcid Ca(OH)2 to the area - Calcium Hydroxide 

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EFFECTS OF ACID RAIN ON PLANTS

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WHAT EFFECTS THE RATE OF WEATHERING? 2000 years to weathering/centimeter of limestone   Climate - major influence on chemical weathering variables: precipitation temperature evaporation   Interactions of temperature and precipitation has the greatest effect.

Chemical weathering predominates in climate with warm temperature, abundant rainfall and lush vegetation.

H2O + CO2 H2CO3 (Carbonic acid - accelerates chemical weathering

Location: Central America, S.E. Asia  

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WEATHERING Physical Weathering - dominates cool, dry climates where H2O

undergoes repeated freezing and thawing. Extremely cold climates has no chemical weathering

  Rock Type and Composition - Characteristics of rocks - hardness and

resistance to breakdown is dependent on the type and composition of the rock.

  Easy - Sedimentary - easy to break Igneous Metamorphic - hardest   Mechanical Weathering - breaking rocks in small pieces - increases

surface area   Topography - flat level area - rocks remain in place and undergo changes Hilly area - rocks suffer greater erosion through mass movement    

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MOVEMENT Erosion - movement of material   Deposition - materials that are dropped in an area after

movement   Gravity - associated with erosion - pull materials downward   “Agent of Mass Movement” (landslides, mudflows,

avalanches) Running water - greatest erosional agent, stronger than

wind, carries more material a greater distance  

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GULLY EROSION IN A PASTURE RUNNING WATER THAT BECOMES DEEP AND WIDE (3 METERS)

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RILL EROSION- RUNNING WATER IN SMALL CHANNELS ON SLOPES

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COASTAL DEPOSITION AND EROSION Mississippi carries 750 million metric tones of material

— deposited into the Gulf of Mexico - forms the delta.

  Volume of river flow and the action of tides determine

the shape of delta. Ocean currents and tides carve out cliffs, arches and other features. Sand particles accumulate on shorelines and form dunes and beaches

Sand bars - accumulation of sand underwater create a barrier island - location: lakes, Gulf of Atlantic Coast 

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LANDFORM DEPOSITION

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SAND BAR

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AMAZON DELTA

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GLACIAL EROSION Glaciers cover 10% of the earth. Erosion is large scale and dramatic.

Landscape features - waterfalls, lakes, Ex. Great Lakes, finger lakes (New York)

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FINGER LAKES NEW YORK

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WIND EROSION Areas of limited precipitation and high temperature, Ex. Death Valley 

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WIND EROSION

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AFTER THE WINDS SUBSIDE

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FARMING METHODS Stops erosion, conserve moisture, trap

blowing snow and protect crops - wind barriers ( wind breakers - thick

line of trees)  Planting methods Plowing methods

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COMBINE DIFFERENT CROPS

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PLANTING CROPS PERPENDICULAR ON A HILL

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NO TILL FARMING

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STRIP FARMING

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DUST BOWL PREVENTION

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FORMATION OF SOIL

Development of Soil - Soil looses covering of broken rock particles and decaying organic matter called humus. Overlays the bedrock.

Result of chemical and mechanical weathering and also biological activity. 

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SOIL Soil composition - Soil forms layers. Pieces of rock are broken off from

the parent rock. Soil is located above it’s parent rock. H2O sinks down carrying minerals and nutrients through the layer of the

soil. Parent rock determines the kinds of minerals, proportion of mineral in soil. Length of formation time depends on the type of rock and climate conditions

  Soil profile - vertical segments of soil layers - well developed soil -

distinct layer 3 main horizons: A - organic/humus - gradual to black color B - poorer developed - rich in clay minerals, forms hardpan layers of soil. Red or brown (iron oxide) C - Directly above bed rock, most weathered parent material    

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SOIL HORIZONS

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TOPOGRAPHY Affects the thickness of developing soil. Sloped areas cause particles, little particles

are washed away. Soil then, is infertile. South facing slope has more direct sunlight / more vegetation, thick soil.

*Valley - soil thick and rich. Vegetation contributes to the buildup of humus and supplies acids to promote the weathering process.

   Soil Types - Appearance, rate of formation

and productivity is determined by climate

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SOIL Soil varies because of different parent

rocks and undergo different climate conditions.

Types of plants: animals that live there: topography: length of time the soil has been forming.

Soils are classified based on climate conditions.

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FOUR TYPES OF SOIL 1 polar 2 temperate 3 desert 4 tropical

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POLAR SOIL

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TEMPERATE SOIL

Supports diverse environments, annual rainfall 50-60 cm, grasslands - abundance of humus, forest - aluminum rich clays

Western U.S. rainfall less than 50-60 cm, support grasses and bushes

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TEMPERATE SOIL SANTA CLARA CA

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DESERT SOIL Low level precipitation - Less than 25

cm of rainfall per year - High level of salts - supports limited

vegetation - light in color— composed of salts and gypsum

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DESERT SOIL

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TROPICAL SOIL- REDDISH IN COLLOR

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COMPARISON OF SOIL PROFILE AND CLIMATE

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PHYSICAL PROPERTIES OF SOIL

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SOIL FERTILITYSoil Fertility - measure how well a soil can support the growth of plants. Factors affect it1) availability of nutrients and minerals2) Number of microorganisms present3) Amount of precipitation4) Topography5) Level of acidityNatural/commercially produce. Fertilizers are added to replace minerals. Add nitrates, phosphates, and phosphorus to the soil. Limestone (pulverized) added to soil to reduce acidity and influence crop growth