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 steep.

Mechanical Weathering

Section 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.

Section 1 WeatheringChapter 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 weathering.

Chemical Weathering

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 GroundwaterWhen acidic groundwater comes into contact with limestone, the limestone is dissolved and forms karst features.

Acid in groundwater has weathered limestone to form Rusty’s Cave in Dade County, Georgia.

Acid in groundwater has

weathered limestone to

form Rusty’s Cave in

Dade County, Georgia.

Chemical weathering:

the process by which

rocks break down as a

result of chemical

reactions.

Chemical Weathering of Granite

Chemical Weathering, continued

2 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.

Lichens, which

consist of fungi and

algae living

together, contribute

to chemical

weathering.

Section 1 WeatheringChapter 10

Oxidation

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 mountain.

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 SoilChapter 10

Residual and Transported Soil

Click below to watch the Visual Concept.

Visual Concept

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

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.

Soil Properties, continued 2 Soil Fertility A soil’s

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.

Soil Layers

Section 3 From Bedrock to SoilChapter 10

Leaching

Click below to watch the Visual Concept.

Visual Concept

Soil and Climate

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.

Lush tropical

rain forests

have

surprisingly

thin topsoil.

Soil and Climate, cont’d

Temperate Forest and Grassland ClimatesTemperate 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.

The rich

soils in

areas that

have a

temperate

climate

support a

vast

farming

industry.

Arctic soils,

such as the

soil along

Denali

Highway, in

Alaska,

cannot

support

lush

vegetation.

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 live.

Water Storage Without soil to hold water, plants would not get the moisture or the nutrients they need.

Soil Damage & 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 of the canyons.

Contour Plowing & 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.

Cover Crop & 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.

Dust Bowl In the 1800’s 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 1930’s, 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 Steinbeck’s “The Grapes of Wrath”