Weathering and Soil Formation Chapter 10
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. Old and New Mountains
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. Mechanical WeatheringSection 1
Chapter 10 Section1 Weathering Ice Wedging Click below to watch the Visual Concept. Visual Concept
Mechanical Weathering, continued 2 • PlantsAs 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 that burrow in the ground break up soil and loosen rocks to be exposed to further weathering. Animals and Mechanical Weathering
WaterEven hard rock, such as granite, can be broken down by water. The next slide shows how this can happen. Acid PrecipitationThe 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. Chemical Weathering Chemical weathering: the process by which rocks break down as a result of chemical reactions.
Acids in Living ThingsSome living things, such as lichens, produce acids that can slowly break down rocks. AirOxygen in the air causes oxidation. Oxidation is the chemical reaction in which an element, such as iron, combines with oxygen to form an oxide. Chemical Weathering, continued2 Lichens, which consist of fungi and algae living together, contribute to chemical weathering.
Chapter 10 Section1 Weathering Oxidation Click below to watch the Visual Concept. 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.
Rock Composition • Rock Composition-rocks made of softer minerals will weather faster than rocks made of harder minerals
Surface AreaThe more surface area of a rock that is exposed to weathering, the faster the rock will be worn down. Increasing the Rate of WeatheringIf a large rock is broken down into smaller fragments, weathering of the rock happens much more quickly. The Shape of Rocks
Weathering and Climate • What Is Climate?Climate is the average weather condition in an area over a long period of time. • Temperature and WaterThe rate of chemical weathering happens faster in warm, humid climates. Water also increases the rate of mechanical weathering.
High ElevationsRocks at higher elevations, as on a mountain, are exposed to more wind, rain, and ice than rocks at lower elevations. Steep SlopesThe 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. Weathering and Elevation
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.
Chapter 10 Section3 From Bedrock to Soil Residual and Transported Soil Click below to watch the Visual Concept. Visual Concept
Soil Ch. 11
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. Loam
Soil Texture and Soil StructureSoil texture is the soil quality that is based on the proportions of soil particles. Soil structure is the arrangement of soil particles. Soil Properties Transported soil may be moved long distances from its parent rock by rivers, such as this one.
Soil FertilityA soil’s ability to hold nutrients and to supply nutrients to a plant is described as soil fertility. Soil HorizonsBecause of the way soil forms, soil often ends up in a series of layers called horizons. Soil pHSoils can be acidic or basic. The pH scale is used to measure how acidic or basic a soil is. Soil Properties 2
Chapter 10 Section3 From Bedrock to Soil Leaching Click below to watch the Visual Concept. Visual Concept
A term that describes the weathered material that is on top of the bed rock Top soil is the top layer of regolith Regolith protects the rock below from weathering because bedrock weathers easier than regular rock Regolith
A soil texture triangle is used to classify the texture of a soil. The sides of the soil texture triangle are scaled for the percentages of sand, silt, and clay. Clay percentages are read from left to right across the triangle Silt is read from the upper right to lower left Sand from lower right towards the upper left portion of the triangle . The intersection of the three sizes on the triangle give the texture class. For instance, if you have a soil with 20% clay, 60% silt, and 20% sand it falls in the "silt loam" class. Soil Triangle
Tropical Rain Forest ClimatesThe warm soil in tropical rain forest climates allows dead plants and animals to decay easily. This provides rich humus to the soil. Desert ClimatesThe lack of rain in desert climates leads to low rates of chemical and mechanical weathering. Soil and Climate Lush tropical rain forests have surprisingly thin topsoil. The salty conditions of desert soils make it difficult for many plants to survive.
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 ClimatesIn arctic climates, as in desert climates, chemical weathering occurs very slowly. Low temperatures slow the formation of humus. Soil and Climate 2 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.
NutrientsSoil provides minerals and other nutrients for plants. All animals get their energy from plants. HousingSoil provides a place for animals to live. Water StorageWithout soil to hold water, plants would not get the moisture or the nutrients they need. The Importance of SoilSection 4
Soil Damage and Loss • OveruseOverused soil can lose its nutrients and become infertile. • Soil ErosionWhen 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 the canyons.
Georgia Red Clay • Georgia is famous for its red clay. • This red color comes from the high iron content in the soil. • Think rust!
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” Dust Bowl
Contour PlowingIn contour plowing, the rows of soil act as a series of dams to prevent water from eroding topsoil away. TerracingIf hills are steep, farmers can use terracing. Terracing changes one steep field into a series of smaller, flatter fields. Contour Plowing and Terracing
Cover CropsCover 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 RotationFarmers can rotate crops that use different nutrients so that nutrients in the soil have time to become replenished. Cover Crop and Crop Rotation