Processes of Change

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Processes of Change
Weathering
chemical weathering
mechanical weathering
moving water
erosion
ice
deposition
waves
gravity
wind
glaciers
Acids
abrasion
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EQ
EQ

• How does weathering
• occur?

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Weathering

• Describe three ways abrasion occurs in nature.
• List three things that cause chemical weathering
  of rocks.
• Describe the similarity in the ways tree roots
  and ice mechanically weather rock.
• Describe five (5) sources of chemical weathering.

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Weathering

• Weathering is the process by which rock materials
  are broken down by the action of physical or
  chemical processes.
• Mechanical weathering is the breakdown of rock
  into smaller pieces by physical means. (ice,
  wind, water, gravity, plants, animals)
• Chemical weathering is the process by which rocks
  break down as a result of chemical reactions.
  Water, weak acids, and air can cause chemical
  weathering.

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6 Agents of Mechanical Weathering

• 1. Ice water seeps into cracks during warm
  weather. When the temperature drops, the water
  freezes and expands, causing the ice to push
  against the sides of the crack. This causes the
  crack in the rock to widen.
• Abrasion the grinding and wearing away of rock
  surfaces through mechanical action of other rock
  or sand pebbles.
• The three ways that can cause abrasion are wind,
  water, and gravity.

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Three Causes of Abrasion

• 2. Water as rocks and pebbles roll along the
  bottom of flowing water, they bump and scrape
  against each other, causing these rocks to become
  rounded and smooth.
• 3. Wind wind blows sand and silt against
  exposed rock eventually wearing away the rocks
  surface.
• 4. Gravity rocks grind against each other
  during a rock slide, creating smaller and smaller
  rock fragments. Anytime one rock hits another
  rock, abrasion takes place.

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Plants and Animals

• Some plants (6) can easily break rocks. The
  roots grow through existing cracks in rocks.
• The growth causes the root to expand, forcing
  the crack to widen. The force can eventually
  split the rock apart.
• 7. Animals that live in the soil (moles, prairie
  dogs, insects, worms, gophers), cause a lot of
  weathering. By burrowing in the ground, these
  living creatures brake up soil and loosen rocks
  to be exposed to further weathering.

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5 Agents of Chemical Weathering

• Common agents of chemical weathering are water,
  acids, and air.
• These agents weaken the bonds between minerals
  grains of the rock.
• 1. Water can cause rock to be broken down and
  dissolve. Can take thousands of years to take
  place.
• 2. Air the process of oxidation is a chemical
  reaction in which an element (iron) combines with
  oxygen, causing rust.
• (Weak Acids) - acid precipitation, acids in
  groundwater, acids in living things.

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Three Sources of Weak Acids

• 3. Acid Precipitation rain, sleet, or snow that
  contains a high concentration of acid. Normal
  precipitation is acidic, acid precipitation
  contains more acid than normal.
• 4. Acids in Groundwater carbonic acid or
  sulfuric acid reacts with rocks in the ground,
  causing a chemical reaction, eating away at the
  rock.
• 5. Acids in Living Things Lichens produce acids
  that slowly break down rock.

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Summary

• Ice wedging is a form of mechanical weathering in
  which water seeps into rock cracks and then
  freezes and expands.
• Wind, water, and gravity cause mechanical
  weathering by abrasion.
• Animals and plants cause mechanical weathering by
  turning the soil and breaking apart rocks.
• Water, acids, and air chemically weather rock by
  weakening the bonds between mineral grains of the
  rock.

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Rates of Weathering

• What is differential weathering?
• How does surface area affect the rate of
  weathering?
• How does climate affect the rate of weathering?
• Why do mountaintops weather faster than rocks at
  sea level?

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Differential Weathering

• Differential weathering is a process by which
  softer, less weather resistant rocks wear away
  and leave harder, more weather resistant rocks
  behind.
• Hard rocks weather more slowly than softer rocks.

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The Shape of Rocks

• Weathering takes place on the outer surface of
  rocks.
• The more surface area exposed to weathering, the
  faster the rock will be worn down.
• As the surface area increases, the rate of
  weathering also increases.
• If a large rock is broken into smaller pieces,
  weathering of the rock happens much faster.
• The rate of weathering increases because a
  smaller rock has more surface area to volume than
  a larger rock.
• More of the smaller rock is exposed to the
  weathering process.

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Weathering and Climate

• The rate of chemical weathering is faster in
  warm, humid climates than cold, dry climates
  because of oxidation.
• Oxidation happens when the temperature is higher
  and when water is present.
• Water increases the rate of mechanical (physical)
  weathering (ice wedging).
• Repeated changes in temperature (freeze, thaw,
  freeze, thaw) is a major factor in mechanical
  weathering.

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Weathering and Elevation

• Mountaintops weather faster than rocks at sea
  level because they are exposed to more wind,
  rain, and ice than rocks at sea level or lower
  elevations.
• The increase in wind, rain, and ice increases the
  effects of mechanical and chemical weathering.
  This increase in elevation causes peaks of
  mountains to weather faster.
• Gravity affects the rate of weathering
• Steepness
• Rainwater
• Removal of sediment exposes new rock to
  weathering
• Abrasion
• Increased surface area of mountain

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Summary

• Hard rocks weather more slowly than softer rocks.
• The more surface area of a rock that is exposed
  to weathering, the faster the rock will be worn
  down.
• Chemical weathering occurs faster in warm, humid
  climates.
• Weathering occurs faster at high elevations
  because of an increase in ice, rain, and wind.

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From Bedrock to Soil

• What is soil (loam) formed from?
• What is bedrock?
• What is soil structure?
• What is humus?
• What are soil horizons?

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The Source of Soil

• Soil is a loose mixture of small mineral
  fragments, organic matter, water, and air that
  can support the growth of vegetation.
• Bedrock is the layer of rock beneath soil.
• Parent rock is the rock formation that is the
  source of soil.
• Wind, water, and movements of glaciers can
  transport or move soil from one place to another.

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Soil Properties

• Soil is made from different-sized materials.
• Soil texture is the soil quality is based on the
  proportions of soil particles.
• Soil texture can influence the ability of water
  move through the soil.
• Soil structure is the arrangement of soil
  particles.

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Soil Properties

• Some soils are rich in nutrients, some are poor
  in nutrients.
• A soils ability to hold nutrients and to supply
  nutrients to a plant is describe as soil
  fertility.
• Humus is the dark, organic material formed in
  soil from the decayed remains of plants and
  animals.

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Soil Horizons

• Soil horizons are the horizontal layers of soil.
• The top layer of soil is called topsoil,
  containing more humus than the other layers of
  soil, rich in nutrients plants need to be
  healthy.
• Good topsoil is necessary for farming.

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Summary

• Soil (loam) is formed from the weathering of
  bedrock.
• Soil texture affects how soil can be worked for
  farming and how well water passes through it.
• The ability of soil to provide nutrients so that
  plants can survive and grow is called soil
  fertility.

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Soil Conservation

• Why is soil important?
• How can human activity affect soil erosion?
• What are three important benefits that soil
  provides?
• List five methods of soil conservation.

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Soil Conservation

• Soil can be endangered, just like plants and
  animals.
• It takes thousands of years for soil to form, it
  is not easy to replace.
• Soil conservation is a method to maintain the
  fertility of the soil by protecting the soil from
  erosion and nutrient loss.

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The Importance of Soil

• Soil provides minerals and other nutrients for
  plant life.
• All animals get their energy from plants.
• Soil also provides a place for animals to live.
• The region a plant or animal lives is called a
  habitat.
• Soil holds water for plants to get the moisture
  or nutrients they need.

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The Processes of Change

• Lesson 18

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Processes of Change (5)

• Weathering and erosion wear down, deposition
  fills in Earths surface.
• Weathering is the slow wearing away or breaking
  down of objects exposed to Earths atmosphere
• Two kinds of weathering act on Earths surface
• Mechanical weathering
• Chemical weathering

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Mechanical Weathering (4)

• When objects are broken down into small pieces
  but their chemical makeup doesnt change
• Wind and moving water are two main causes of
  mechanical weathering
• Repeated changes in temperature (freeze, melt,
  freeze, melt again)

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Chemical Weathering (5)

• Material of an object is changed
• Produces underground caverns
• Statue of Liberty needed repairs because of
  chemical weathering
• Examples
• Rust
• Acid rain

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Erosion (5)

• The natural moving of material from one place to
  another
• Erosion transports weathered rock material
• Causes of Erosion
• Moving water
• Gravity
• Wind
• Glaciers (moving rivers of ice)
• Waves

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Deposition (5)

• Land torn down in one place is deposited in
  another place
• Gravity can cause a landslide moving mud, rock
  and soil down a hill
• Wind erosion can move sand and deposit it in
  another area
• Glaciers (rivers of ice) scrape rocks off the
  land and moves them downhill

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Deposition (5)

• Glaciers will stop moving and even retreat and
  cut a steep U-shaped valley in the land
• Erosion caused by mountain rivers form V-shaped
  valleys
• Hurricanes create waves that erode beaches and
  cliffs
• Breaking of waves on a beach can wear it away.
  The larger the waves, the faster is the rate of
  erosion.