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Weathering and Soil Formation


Weathering and Soil Formation Chapter 10 – PowerPoint PPT presentation

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Title: Weathering and Soil Formation

Weathering and Soil Formation
  • Chapter 10

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
  • The Appalachians are much older so they have had
    more time to weather and erode.

  • The natural processes that break down exposed
    rock and turns it into soil.
  • Heat, cold, water, and ice, and wind all can
    weather rock.
  • Rocks get weathered into smaller and smaller
    pieces, forming the basis of soil.

Mechanical Weathering Section 1
  • Mechanical (physical) weathering is when rock is
    physically broken into smaller pieces.
  • 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.

Section 1 Weathering
Chapter 10
Ice Wedging
Click below to watch the Visual Concept.
Visual Concept
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.

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

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.

Chemical weathering the process by which rocks
break down as a result of chemical reactions. A
new substance is created.
Chemical Weathering of Granite
Chemical Weathering, continued 2
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

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

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.

Surface Area and Volume
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.

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

The Source of Soil Section 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.

Section 3 From Bedrock to Soil
Chapter 10
Residual and Transported Soil
Click below to watch the Visual Concept.
Visual Concept
  • Ch. 11

  • 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.

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.
Soil Texture
Soil Properties 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
  • Soil pH Soils can be acidic or basic. The pH
    scale is used to measure how acidic or basic a
    soil is.

Soil Layers
Section 3 From Bedrock to Soil
Chapter 10
Click below to watch the Visual Concept.
Visual Concept
  • 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 than regular rock

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.  

Soil and Climate
Lush tropical rain forests have surprisingly thin
  • 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.
Soil and Climate 2
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
The Importance of Soil Section 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
  • Water Storage Without soil to hold water, plants
    would not get the moisture or the nutrients they

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.
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
Georgia Red Clay
  • Georgia is famous for its red clay.
  • This red color comes from the high iron content
    in the soil.
  • Think rust!

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
  • In the 1930s, severe drought over several years
    allowed this soil to be blown away in great, dark
  • 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
  • Read Steinbecks The Grapes of Wrath

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 use
    terracing. Terracing changes one steep field into
    a series of smaller, flatter fields.

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
  • Crop Rotation Farmers can rotate crops that use
    different nutrients so that nutrients in the soil
    have time to become replenished.