soil weathering erosion.notebook
March 19, 2014
What is soil?
Soil, Weathering, and Erosion
• Book definition: A loose mixture of small mineral fragments and organic material.
What is under the soil layer?
• If you dig and dig, what will you hit? • The layer of rock beneath soil is called bedrock. • Soil formation occurs when bedrock is broken down by weathering.
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What is the purpose of soil?
• Plants depend on soil for water and support. Nutrients such as potassium, phosphorus, and nitrogen are part of soil. • Houses, cities, and roads are built on soil.
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Soil Facts: • The main component of soil is weathered rock particles • Soil is a mixture of rock particles, humus, water, and air • Humus decayed matter in the soil(mostly from plants and animals) • Soil layers called horizon, are separated by their composition and characteristic. • Different Soil Horizons put together is called a soil profile.
Soil Facts
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soil weathering erosion.notebook
Can you describe what you see in each horizon (layer) of the soil profile
March 19, 2014
What are the soil layers?
O A B C http://soils.usda.gov/education/resources/lessons/profile/
Soil Profile
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Check and see! O Horizon: Contains the majority alive and decayed organic material (humus) A Horizon: Made of humus. Rich in minerals. Known as the topsoil Dark in color.
B Horizon: Mostly made of clay Very little minerals seep down Reddish and brownish in color
LET
'S
REV
IEW
C Horizon: No organic material Unweathered rock Yellowish in color D Horizon - (not shown) Large unweathered rock Bedrock
Answer to Profile
http://soils.usda.gov/education/resources/lessons/profile/
Move the blocks to reveal the answers!
Review Questions
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soil weathering erosion.notebook
March 19, 2014
The upper layer of soil and is commonly called topsoil. Humus O Horizon
A Horizon
B Horizon
C Horizon
It contains clay and minerals that have leached down from the top horizon Humus O Horizon
Question 1
B Horizon
Question 5
C Horizon
The deepest layer of soil. Consists of largest and leastweathered rock particles. A Horizon
A Horizon
B Horizon
Question 4
In a soil profile, most of the organic material is found in the:
Humus O Horizon
A Horizon
B Horizon
C Horizon
D Horizon
C Horizon
Question 6
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soil weathering erosion.notebook
March 19, 2014
How do rocks break down into soil? Mechanical/Biological Weathering
• Weathering is the breaking down of rocks and other materials on Earth’s surface.
• Involves only physical changes. • Occurs as a result of temperature changes and ice wedging, and root action.
• Two kinds of weathering: Mechanical/biological weathering Chemical weathering
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Chemical Weathering
Mechanical or Chemical Weathering?
• Substances in water cause rocks to dissolve. Minerals change into other substances. • Usually caused by reactions with oxygen, water, or acids. • Most chemical weathering is caused by water. • Carbon dioxide can dissolve in to form carbonic acid.
water
Frozen glacial water
Nevada’s Valley of Fire
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soil weathering erosion.notebook
Mechanical or Chemical Weathering?
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Mechanical or Chemical Weathering?
Tree on a cliff
Lamb cemetery marker
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Mechanical or Chemical Weathering?
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Rocks are broken down. Now what happens?
• Erosion happens. • Erosion is the process by which weathered material is removed and carried from a place.
Agents of Erosion
• Running water, glaciers, wind, waves, and gravity are the five most common agents of erosion. Parthenon
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soil weathering erosion.notebook
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erosion gradual change in landforms through wearing away of soil and rock caused by wind, water, or some other natural force .
Beach Erosion
Imagine that the river started up here!
Believe it or not, this rock formation resulted from wind erosion. Smaller, lighter chunks of rock broke off and blew away until this formation was all that remained.
Glacial Erosion
glacier
Erosion caused by water; millions of years ago before the Grand Canyon was formed, the Colorado River was a quiet river streaming through the land.
glacial erosion
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SLOW MASS MOVEMENT Slow mass movement can occur over days, weeks or years and can be identified by bending trees, leaning fences and cracked roads.
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Deposition
Erosion breaks rocks down, but deposition is the process where the material is dropped in new places. Deposition builds landforms on Earth.
Creep
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soil weathering erosion.notebook
March 19, 2014
Dust bowl of the 1930s This is what a native grassland would have looked like in Kansas, Oklahoma, Texas, and Colorado when pioneers first arrived.
• For eight years the dust storms blew across the southern Plains. • Began in 1931. • Land had been over‐plowed and over‐grazed.
Click in the empty space to see what the land looked like in the Dust Bowl of the 1930s.
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April 27, 1935: Congress declares soil erosion "a national menace“. Farming techniques such as terracing, crop rotation, contour plowing, and cover crops were advocated. Farmers were paid to practice soil‐conserving farming techniques.
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SOIL CONSERVATION: (4 methods)
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soil weathering erosion.notebook
1. Contour Plowing – farmers plow along the curves of the land to prevent water from washing away soil; rows of garden look curvy instead of straight
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2. Conservation Plowing (NoTill Plowing) – farmers leave the dead plants to keep the soil covered and in place; don’t cut down or plow old crops
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3. Crop Rotation – farmers plant different crops each year that use different nutrients from the soil (corn/cotton àoats/barley/ryeàbeans/alfalfa)
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4. Terracing – farmers plant crop on different levels on a hillside to maximize the area of usable land and keep healthy soil in place; looks like steps on the hill
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