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Weathering: Processes of Change. Weathering. chemical weathering. mechanical weathering. moving water. erosion. ice. deposition. waves. gravity. wind. glaciers. Acids. abrasion. EQ :. How does weathering occur?. Describe three ways abrasion occurs in nature.

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Weathering: Processes of Change

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Weathering processes of change l.jpg

Weathering:Processes of Change


chemical weathering

mechanical weathering

moving water










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How does weathering


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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 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 rock’s 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, weak 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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  • 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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Quick Check

Which of the following things cannot cause mechanical weathering?

  • A. water

  • B. acid

  • C. wind

  • D. animals

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Quick Check

Which of the following is a type of frost action?

  • A. abrasion

  • B. oxidation

  • C. ice wedging

  • D. gravity

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Quick Check

Which of the following types of chemical weathering causes a karst landscape, such as a cavern?

  • A. lichens

  • B. acid precipitation

  • C. acids in groundwater

  • D. water

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Quick Check

How do lichens slowly break down a rock?

  • A. by abrasion

  • B. by mechanical means

  • C. by ice wedging

  • D. by chemical means

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Quick Check

Which of the following will most likely experience oxidation?

  • A. tennis ball

  • B. aluminum can

  • C. wooden fence

  • D. Bicycle tire

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The grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles

Rain, sleet, or snow that contains a high concentration of acids

The process by which rocks break down as a result of chemical reactions

The breakdown of rock into smaller pieces by physical means

A chemical reaction in which an element, such as iron, combines with oxygen to form an oxide

The process by which rock materials are broken down by the action of physical or chemical processes

a. mechanical weathering

b. oxidation

c. weathering

d. acid precipitation

e. abrasion

f. chemical weathering

Quick Check

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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?

Rates of Weathering

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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

  • Mountaintopsweather faster than rocks at sea level because they are exposed to more wind, rain, andice 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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  • 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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Quick Check

1. What three factors determine the rate at which rock weathers?




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Quick Check

2. The process by which softer, less weather-resistant rocks wear away and leave harder, more weather-resistant rocks behind is called

A. mechanical weathering

B. chemical weathering

C. differential weathering

D. acid precipitation

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Quick Check

3. Weathering takes place

  • at different rates

  • on the outer surface of rocks.

  • on all rocks equally.

  • inside the rocks.

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Quick Check

4. Because of a large rock’s volume, it will

  • weather unevenly.

  • weather relatively quickly.

  • not weather at all.

  • weather relatively slowly.

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Quick Check

5. What is the average weather condition in an area over a long period of time called?


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Quick Check

6. Chemical weathering such as oxidation occurs more quickly in a climate that is ___________ and ________________.



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Quick Check

7. Weathering occurs faster at high elevations because of

  • an increase in wind but not ice or rain.

  • an increase in ice and rain but not wind.

  • a decrease in wind, ice, and rain.

  • an increase in wind, ice, and rain.

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What is soil formed from?

What is bedrock

What is humus?

What are soil horizons?

From Bedrock to Soil

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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.

  • Soil that is blown or washed away from its parent soil is called transported 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 based on the proportions of soil particles.

  • Soil texture can influence the ability of water movement through the soil.

  • Soil structure is the arrangement of soil particles.

  • Consistency describes a soil’s ability to be worked and broken up for farming.

  • Infiltration is the ability of water to move through soil.

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Soil Properties

  • Some soils are rich in nutrients, some are poor in nutrients.

  • Soil fertility is the soil’s ability to hold nutrients and to supply nutrients to a plant.

  • 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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Soil pH

  • Soils can be acidic or basic.

  • The pH scale, ranging from 0 to 14, is used to measure the acidity of a substance.

  • 7 is neutral; below 7 is acidic; above 7 is basic.

  • Different plants need different types of soil.

  • The right pH for a soil depends on the plants growing in it.

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  • 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.

  • The pH of a soil influences which nutrients plants can take up from the soil.

  • Different climates have different types of soil, depending on the temperature and rainfall.

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1.Soil that is blown or washed away from its parent rock

2. The layer of rock beneath the soil

3. A rock formation that is the source of mineral fragments in the soil

4. A loose mixture of mineral fragments, organic material, water, and air that can support vegetation

a. soil

b. transported soil

c. parent rock

d. bedrock

Quick Check

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Soil quality based on the proportions of soil particles

The arrangement of soil particles

Ability of water to move through soil

Soil’s ability to be broken up for farming

a. soil structure

b. infiltration

c. consistency

d. soil texture

Quick Check

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Quick Check

What is soil’s ability to hold nutrients and to supply nutrients to a plant?

  • Soil structure

  • Soil texture

  • Soil horizons

  • Soil fertility

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Quick Check

What do we call the removal of substances from soil due to water passing through it?

  • Wedging

  • Infiltration

  • Erosion

  • leaching

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Quick Check

What is the layer of soil that often contains the most humus?

  • Horizon

  • Parent rock

  • Topsoil

  • bedrock

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Quick Check

What is soil that has a pH below 7 called?

  • Neutral

  • Acidic

  • Basic

  • midpoint

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Quick Check

What is the correct pH for growing plants?

  • 7

  • Above 7

  • Below 7

  • It depends upon the plant

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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.

Soil Conservation

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Soil Conservation

  • Soil can be endangered, just like plants and animals.

  • Soil is important because it provides nutrients to plants, provides houses for animals, and stores water.

  • 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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Soil Loss and Damage

  • Soil loss is a serious problem around the world.

  • Soil damage leads to soil loss.

  • Soil becomes damaged from overuse, by poor farming techniques.

  • Soil damage also can come from overgrazing.

  • Overused soil can lose its nutrients and become infertile

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Soil Loss and Damage

  • Plants will not grow in soil that is infertile.

  • Without plants to hold and help the cycle water, the area can become a desert.

  • Without plants and moisture, soil can be blown or washed away.

  • Soil left unprotected can be exposed to erosion.

  • Roots from plants and trees act like an anchor to hold soil in place.

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Soil Erosion

  • Human activity can accelerate soil erosion when those activities affect plant roots.

  • Plants and trees protect the soil.

  • By taking care of the vegetation, you also take care of the soil.

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  • Soil is important for plants to grow, for animals to live in, and for water to be stored.

  • Soil erosion and soil damage can be prevented by no-till farming, contour plowing, terracing, using cover crop, and practicing crop rotation.

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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 Earth’s surface.

  • Weathering is the slow wearing away or breaking down of objects exposed to Earth’s atmosphere

  • Two kinds of weathering act on Earth’s surface

    • Mechanical weathering

    • Chemical weathering

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Mechanical Weathering (4)

  • When objects are broken down into small pieces but their chemical makeup doesn’t 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 transportsweathered 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.

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