Weathering and Soil Formation

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Weathering and Soil Formation

• Chapter 10

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Old and New Mountains

• The Appalachian Mountains appear very different
  from the Sierra Mountains.
• The Appalachians are smaller, rounded, gently
  sloping, and covered with plants.
• The Sierras are twice as high, and very rocky and
  steep.

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Mechanical WeatheringSection 1

• Ice The alternate freezing and thawing of soil
  and rock, called frost action, is a form of
  mechanical weathering.
• Abrasion Abrasion is the grinding and wearing
  away of rock surfaces through the mechanical
  action of other rock or sand particles.
• Wind, Water, and Gravity Wind, water, and
  gravity carry rocks, causing them to abrade
  against one another.

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Section 1 Weathering
Chapter 10
Ice Wedging
Click below to watch the Visual Concept.
Visual Concept
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Mechanical Weathering, continued 2

• Plants As a plant grows, the force of the
  expanding root becomes so strong that it can
  break a rock apart.
• Animals Almost any animal that burrows causes
  mechanical weathering by mixing and digging
  through soil and rock particles.

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Animals and Mechanical Weathering

• Animals that burrow in the ground break up soil
  and loosen rocks to be exposed to further
  weathering.

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Chemical Weathering
Acid in groundwater has weathered limestone to
form Rustys Cave in Dade County, Georgia.

• Water Even hard rock, such as granite, can be
  broken down by water. The next slide shows how
  this can happen.
• Acid Precipitation The high level of acidity in
  acid precipitation can cause very rapid
  weathering of rock.
• Acids in Groundwater When acidic groundwater
  comes into contact with limestone, the limestone
  is dissolved and forms karst features.

• Acid in groundwater has weathered limestone to
  form Rustys Cave in Dade County, Georgia.

Chemical weathering the process by which rocks
break down as a result of chemical reactions.
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Chemical Weathering of Granite
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Chemical Weathering, continued2
Lichens, which consist of fungi and algae living
together, contribute to chemical weathering.

• Acids in Living Things Some living things, such
  as lichens, produce acids that can slowly break
  down rocks.
• Air Oxygen in the air causes oxidation. Oxidation
  is the chemical reaction in which an element,
  such as iron, combines with oxygen to form an
  oxide.

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Section 1 Weathering
Chapter 10
Oxidation
Click below to watch the Visual Concept.
Visual Concept
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Differential WeatheringSection 2

• What Is Differential Weathering? Differential
  weathering is a process by which softer, less
  weather resistant rock wear away and leave
  harder, more weather resistant rock. The image
  below is an example of differential weathering.

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The Shape of Rocks

• Surface Area The more surface area of a rock that
  is exposed to weathering, the faster the rock
  will be worn down.
• Increasing the Rate of Weathering If a large rock
  is broken down into smaller fragments, weathering
  of the rock happens much more quickly.

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Surface Area and Volume
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Weathering and Climate

• What Is Climate? Climate is the average weather
  condition in an area over a long period of time.
• Temperature and Water The rate of chemical
  weathering happens faster in warm, humid
  climates. Water also increases the rate of
  mechanical weathering.

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Weathering and Elevation

• High Elevations Rocks at higher elevations, as on
  a mountain, are exposed to more wind, rain, and
  ice than rocks at lower elevations.
• Steep Slopes The steepness of mountain slopes
  increases the effects of mechanical and chemical
  weathering. Steep slopes cause water and
  sediments to quickly run down the side of the
  mountain.

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The Source of SoilSection 3

• What Is Soil? Soil is a loose mixture of small
  mineral fragments, organic material, water, and
  air that can support the growth of vegetation.
• Residual and Transported Soil Soil that remains
  above its parent rock is called residual soil.
  Soil that is blown or washed away from its parent
  rock is called transported soil.

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Section 3 From Bedrock to Soil
Chapter 10
Residual and Transported Soil
Click below to watch the Visual Concept.
Visual Concept
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Soil Properties

• Soil Texture and Soil Structure Soil texture is
  the soil quality that is based on the proportions
  of soil particles. Soil structure is the
  arrangement of soil particles.

Transported soil may be moved long distances from
its parent rock by rivers, such as this one.
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Soil Texture
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Loam

• Loam, a type of very fertile soil is made up of
  air, water and organic materials as well as
  minerals from weathered rock.
• Rich fertile soil that is made up of about equal
  parts of clay sand and silt.

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Soil Properties, continued 2

• Soil Fertility A soils ability to hold nutrients
  and to supply nutrients to a plant is described
  as soil fertility.
• Soil Horizons Because of the way soil forms, soil
  often ends up in a series of layers called
  horizons.
• Soil pH Soils can be acidic or basic. The pH
  scale is used to measure how acidic or basic a
  soil is.

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Soil Layers
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Section 3 From Bedrock to Soil
Chapter 10
Leaching
Click below to watch the Visual Concept.
Visual Concept
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Regolith

• A term that describes the weathered material that
  is on top of the bed rock
• Top soil is the top layer of regolith
• Regolith protects the rock below from weathering
  because bedrock weathers easier then regular rock
  

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Soil Triangle

• A soil texture triangle is used to classify the
  texture of a soil.
• The sides of the soil texture triangle are scaled
  for the percentages of sand, silt, and clay.
• Clay percentages are read from left to right
  across the triangle
• Silt is read from the upper right to lower left
• Sand from lower right towards the upper left
  portion of the triangle
• . The intersection of the three sizes on the
  triangle give the texture class. For instance, if
  you have a soil with 20 clay, 60 silt, and 20
  sand it falls in the "silt loam" class.  

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Soil and Climate
Lush tropical rain forests have surprisingly thin
topsoil.

• Tropical Rain Forest Climates The warm soil in
  tropical rain forest climates allows dead plants
  and animals to decay easily. This provides rich
  humus to the soil.
• Desert Climates The lack of rain in desert
  climates leads to low rates of chemical and
  mechanical weathering.

The salty conditions of desert soils make it
difficult for many plants to survive.
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Soil and Climate, continued2
The rich soils in areas that have a temperate
climate support a vast farming industry.

• Temperate Forest and Grassland Climates Temperate
  forest and grassland climates get enough rain to
  cause a high level of chemical weathering, but
  not too much that nutrients are leached out.
• Arctic Climates In arctic climates, as in desert
  climates, chemical weathering occurs very slowly.
  Low temperatures slow the formation of humus.

Arctic soils, such as the soil along Denali
Highway, in Alaska, cannot support lush
vegetation.
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The Importance of SoilSection 4

• Nutrients Soil provides minerals and other
  nutrients for plants. All animals get their
  energy from plants.
• Housing Soil provides a place for animals to
  live.
• Water Storage Without soil to hold water, plants
  would not get the moisture or the nutrients they
  need.

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Soil Damage and Loss

• Overuse Overused soil can lose its nutrients and
  become infertile.
• Soil Erosion When soil is left unprotected, it
  can be exposed to erosion. Erosion is the process
  by which wind, water, or gravity transport soil
  and sediment from one location to another.

Providence Canyon, Georgia, shows the effects of
cutting forests for farm land.
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Providence Canyon
Providence Canyon is near Lumpkin, Georgia.  It
has beautiful gullies formed by erosion 150 years
ago. This park is part of Georgia's East Gulf
Coastal Plain region. People call it Georgia's
"Little Grand Canyon."  There are 16 canyons
altogether.  Some canyons are 1 mile long and 300
feet across.  An ancient ocean formed all the
canyons.
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Contour Plowing and Terracing

• Contour Plowing In contour plowing, the rows of
  soil act as a series of dams to prevent water
  from eroding topsoil away.
• Terracing If hills are steep, farmers can using
  terracing. Terracing changes one steep field into
  a series of smaller, flatter fields.

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Cover Crop and Crop Rotation

• Cover Crops Cover crops are crops that are
  planted between harvests to replace certain
  nutrients and prevent erosion. Cover crops
  prevent erosion by providing cover from wind and
  rain.
• Crop Rotation Farmers can rotate crops that use
  different nutrients so that nutrients in the soil
  have time to become replenished.

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Dust Bowl

• In the 1800s settlers in the Great Plains turned
  the fertile, moisture laden sod into farmland.
• In drought, this land dried up and blew away as
  dust.
• In the 1930s, severe drought over several years
  allowed this soil to be blown away in great, dark
  clouds.
• Some of these dust storms reached New York City.
• This lasted until 1938. Many farmers in the
  Dust Bowl had to abandon their homes and move
  away.
• Read Steinbecks The Grapes of Wrath