Weathering and Soil Weathering and Soil FormationFormation

Chapter 10Chapter 10

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

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

Acid in groundwater has weathered limestone to form Rusty’s Cave in

Dade County, Georgia.

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

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, 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.

Section 3 From Bedrock to SoilChapter 10

Leaching

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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, continued2

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.

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 using 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.