Weathering and Soil Weathering and Soil FormationFormation

Chapter 10Chapter 10

Old and New MountainsOld and New Mountains The Appalachian The Appalachian

Mountains appear Mountains appear very different from very different from the Sierra Mountains.the Sierra Mountains.

The Appalachians The Appalachians are smaller, rounded, are smaller, rounded, gently sloping, and gently sloping, and covered with plants.covered with plants.

The Sierras are twice The Sierras are twice as high, and very as high, and very rocky and steep.rocky and steep.

Mechanical Weathering Mechanical Weathering

Mechanical Mechanical Weathering-the Weathering-the breakdown of rock breakdown of rock into smaller pieces by into smaller pieces by physical means physical means

Weathering-is the Weathering-is the process by which rock process by which rock materials are broken materials are broken down by the action of down by the action of physical or chemical physical or chemical processes.processes.

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.

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 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 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 GraniteChemical Weathering of Granite

Chemical Weathering, continued2

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

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Visual Concept

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.

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 VolumeSurface 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 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.

Section 3 From Bedrock to SoilChapter 10

Residual and Transported Soil

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Visual Concept

SoilSoil

Ch. 11Ch. 11

LoamLoam

Loam, a type of very Loam, a type of very fertile soil is made fertile soil is made up of air, water and up of air, water and organic materials as organic materials as well as minerals well as minerals from weathered from weathered rock.rock.

Rich fertile soil that Rich fertile soil that is made up of about is made up of about equal parts of clay equal parts of clay sand and silt. 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 TextureSoil Texture

Soil Properties 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 LayersSoil Layers

Section 3 From Bedrock to SoilChapter 10

Leaching

Click below to watch the Visual Concept.

Visual Concept

RegolithRegolith

A term that A term that describes the describes the weathered weathered material that is on material that is on top of the bed rocktop of the bed rock

Top soil is the top Top soil is the top layer of regolithlayer of regolith

Regolith protects Regolith protects the rock below the rock below from weathering from weathering because bedrock because bedrock weathers easier weathers easier than regular rock than regular rock

Soil TriangleSoil Triangle A A soil texture trianglesoil texture triangle is is

used to classify the texture used to classify the texture of a soil. of a soil.

The sides of the soil texture The sides of the soil texture triangle are scaled for the triangle are scaled for the percentages of sand, silt, percentages of sand, silt, and clay.and clay.

Clay percentages are read Clay percentages are read from left to right across the from left to right across the triangletriangle

Silt is read from the upper Silt is read from the upper right to lower left right to lower left

Sand from lower right Sand from lower right towards the upper left towards the upper left portion of the triangleportion of the triangle

. The intersection of the . The intersection of the three sizes on the triangle three sizes on the triangle give the texture class. For give the texture class. For instance, if you have a soil instance, if you have a soil with 20% clay, 60% silt, and with 20% clay, 60% silt, and 20% sand it falls in the "silt 20% sand it falls in the "silt loam" class.  loam" class.  

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 2 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.

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 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.

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 CanyonProvidence CanyonProvidence 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.

Georgia Red ClayGeorgia Red Clay

Georgia is famous for Georgia is famous for its red clay.its red clay.

This red color comes This red color comes from the high iron from the high iron content in the soil.content in the soil.

Think rust!Think rust!

Dust BowlDust Bowl In the 1800’s settlers in the In the 1800’s settlers in the

Great Plains turned the Great Plains turned the fertile, moisture laden sod fertile, moisture laden sod into farmland.into farmland.

In drought, this land dried In drought, this land dried up and blew away as dust.up and blew away as dust.

In the 1930’s, severe In the 1930’s, severe drought over several years drought over several years allowed this soil to be blown allowed this soil to be blown away in great, dark clouds.away in great, dark clouds.

Some of these dust storms Some of these dust storms reached New York City.reached New York City.

This lasted until 1938. This lasted until 1938. Many farmers in the “Dust Many farmers in the “Dust Bowl” had to abandon their Bowl” had to abandon their homes and move away.homes and move away.

Read Steinbeck’s “The Read Steinbeck’s “The Grapes of Wrath”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 rain.

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

Old and New Mountains Old and New Mountains