Weathering and Soil Formation Chapter 10 Weathering Weathering is simply the breakdown of rock into smaller and smaller pieces called sediment. Rocks on the Earth’s surface are undergoing weathering all the time, either by mechanical means or by chemical means. Mechanical Weathering Mechanical weathering is simply the breakdown of rock into smaller pieces by physical means. Agents or causes of mechanical weathering include: Ice Wind Water - gravity - plants - animals Agents of Mechanical Weathering Explain how each of the following Causes mechanical Weathering: Ice (Define Ice Wedging) Wind, Water, and Gravity (Define Abrasion) Plants Animals Chapter 10 Weathering Mechanical Weathering Ice Wedging Ice Wedging occurs when water seeps into cracks of rocks and constantly freezes and thaws expanding the rock and eventually breaking it apart https://www.youtube.com/watch?v=_XnCTcjNpuc http://my.hrw.com/sh2/sh07_10/student/flash/visual_conce pts/80127.htm Mechanical Weathering Abrasion http://my.hrw.com/sh2/sh07_1 0/student/flash/visual_concept s/80130.htm https://www.youtube.com/watc h?v=JA4BdLkiRtg Abrasion: Abrasion is the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles. Mechanical Weathering Wind, Water, and Gravity: Wind, water, and gravity carry rocks, causing them to abrade against one another. Mechanical Weathering (Biological Weathering) Plants As a plant grows, the force of the expanding root becomes so strong that it can break a rock apart. (Biological Weathering) Animals and Mechanical Weathering (Biological Weathering) Animals that burrow in the ground break up soil and loosen rocks to be exposed to further weathering (Biological Weathering) Chemical Weathering Chemical Weathering is the chemical breakdown of rocks and minerals into new substances. The most common agents or causes of chemical weathering are: Water Weak Acids Air Soil Agents of Chemical Weathering Explain how each of the following Causes Chemical Weathering Water Acid Precipitation Acid in Ground Water Acids in Living Things Air (Define and explain the result of Oxidation) Chemical Weathering Water Even hard rock, such as granite, can be broken down by water. Chemical Weathering (Acid Precipitation) Sometimes precipitation contains more acid than normal. Rain, sleet, or snow that contains more acid than normal is called acid precipitation. Acid precipitation forms when small amounts of certain gases mix with water in the atmosphere. The gases come from natural sources, such as active volcanoes. They are also produced when people burn fossil fuels, such as coal and oil. Acid Precipitation The high level of acidity in acid precipitation can cause very rapid weathering of rock. Chemical Weathering (Biological Weathering) Acids in Living Things Some living things, such as lichens, produce acids that can slowly break down rocks. https://www.youtube.com/ watch?v=zv2JNaqnYxU&i ndex=2&list=PLEE924CE 51E2604AD Lichens, which consist of fungi and algae living together, contribute to chemical weathering. Chemical Weathering Acids in Groundwater When acidic groundwater comes into contact with limestone, the limestone is dissolved and forms karst features. When the groundwater touches some kinds of rock, a chemical reaction happens. The chemical reaction dissolves the rock. Over a long period of time, huge caves can form where rock has been dissolved. Acid in groundwater has weathered limestone to form Rusty’s Cave in Dade County, Georgia. Chapter 10 Oxidation 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. http://my.hrw.com/sh2/sh07_10/student/flash/visual_conce pts/80128.htm https://www.youtube.com/watch?v=6VnVRHIV6j4 Section 10.2 (Rates of Weathering) 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. 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. Soil Ch. 11 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 • 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 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 Layers 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 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 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! 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” Soil Conservation A method to maintain the fertility of the soil by protecting the soil from erosion and chemical decay. The Importance of Soil 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. Why is soil Important? Soil is one of Earth’s most valuable resources because every thing that lives on land depends directly or indirectly on soil. Plants depend directly on the soil to live and grow. Animals depend on plants or on other animals for food. Fertile soil is valuable because there is a limited supply. 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. Soil Damage/ Loss Soil damage can lead to soil loss. Soil can be damaged from overuse by poor farming techniques or by overgrazing. Overused soil can lose its nutrients and become infertile. Plants can’t grow in soil that is infertile. Without plants to hold and help cycle water, the area can become a desert.. 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. Roots from plants and trees are like anchors to the soil. Roots keep topsoil from being eroded. Therefore, plants and trees protect the soil. What human activities affect soil erosion? Farming Construction and development Mining What can be done to prevent soil erosion? Contour Plowing Conservation Plowing Terracing Windbreaks Crop Rotation Contour Plowing and Terracing Contour Plowing In contour plowing farmers plowed rows so that they run up and down hills. 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. Prevents erosion from heavy rains on steep hills No Till Farming and Cover Crop No-till farming, which is the practice of leaving old stalks, provides cover from rain. The cover reduces water runoff and slows soil erosion. 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 and Windbreaks Crop Rotation Farmers can rotate crops that use different nutrients so that nutrients in the soil have time to become replenished. Windbreaks Rows of trees are planted along the edges of fields. Block the wind and also trap eroding soil.