Weathering and Erosion In this chapter we will discuss: The difference between chemical and mechanical weathering and their effects on the climate How soil develops and the factors that affect its development Why soil is important and ways to reduce soil loss

Weathering Weathering breaks down rock into smaller pieces called sediments. The sediments change gradually into soil. Weathering also produces strange rock formations like the one on page 182. (the soil formation depends on the amount of weathering that occurs). There are two types of weathering: chemical and mechanical

Physical Weathering Occurs when rocks are broken apart by physical processes. Their chemical makeup remains the same. It is caused by growing plants, burrowing animals, and expanding ice. The plants are nourished by water and nutrients that seep through cracks. This causes plants to grow. The animals loosen sediments and push them to the surface. Once at the surface other weathering processes act on them.

Ice wedging: occurs in temperate and cold climates where water enters cracks in rocks and freezes. freezing and thawing also breaks up roads and highways As the amount of surface area increases more rock is exposed to water and oxygen.

Chemical Weathering occurs when chemical reactions dissolve the minerals in rock or change them into different minerals. It also occurs when naturally formed acids come into contact with other rocks. Natural acids - Carbonic acids are formed when water mixes with carbon dioxide gas in the air or soil. This causes calcite to dissolve. Clay is an end product of weathering. Kaolinite clay forms when natural acids react with feldspar in granite and other rocks.

Oxidation occurs when metallic minerals are exposed to oxygen and water over prolonged periods of time (ex. limestone) Effects of climate Climate is the pattern of weather that occurs in a particular area over many Years. -in cold climates mechanical weathering breaks down rocks more rapidly.

occurs more rapidly (ex. Amazon). Marble -in warm, wet climates, chemical weathering occurs more rapidly (ex. Amazon). Marble weathers more rapidly than granite in warm climates.

Explain . . . the difference between mechanical and chemical weathering the effects of climate on weathering

Factors Affecting Soil Formation Soil is a mixture of weathered rock, decayed organic matter, mineral fragments, water, and air. The Nature of Soil Factors Affecting Soil Formation Climate Slope of the land Types of rock Types of vegetation And the amount of time a rock has been weathering

Soil Composition Soil is composed of plants, leaves, stems, and animal microorganisms. When animals die they get into the soil and then decay. This decayed matter is called humus. Humus is dark in color and serves as a nutritional source for plants.

Soil Profile Soil is set up in layers called horizons Soil Profile Soil is set up in layers called horizons. These horizons create the soil profile. Most soils have three horizons. Horizon A top layer of soil, also called topsoil. May be covered with twigs, leaves, and other organic material (litter) Litter helps prevent erosions and holds water. It has more humus and mineral particles than any other layer. It is dark in color (color is determined by the organic material that is in the soil)

Horizon B Lighter in color, less fertile Has larger particles Contains material from the leaching process. Leaching removes material from Horizon A through acid, which dissolves minerals from the upper layer.

Soil profile continued Horizon C Consists partially of weathered rock and is the bottom horizon. Composed of coarser, smaller sediments than other horizons above it. Called the parent material of soil . Glacial deposits cover much of the Midwestern U. S. Soil on glaciers are very fertile and are a key part of their (Midwestern states) agricultural industry.

Soil Types Different climates produce different types of soil. The U. S. has 9 different soil types that vary in color, depth, texture, and fertility.

Explain. . . How soil develops from rock The different soil horizons The factors that affect soil developments.

Soil Erosion Soil is important; if topsoil is eroded away, it becomes less fertile.

Causes and Effects of Soil Erosion Soil is eroded when it is moved from the place where it is formed. It is more common on steep slopes and areas where there is little vegetation Soil forms at the same rate it is produced.

Types of Soil Erosion agricultural cultivation: is the result of increase in population. Over time it can reduce soil quality. Forest harvesting: removing forests and exposing soil. This is especially so in tropical rain forests. The soil here is rich in nutrients but only for a few years. Once useless, the land is cleared and the process is repeated, which damages the soil more.

Overgrazing: when natural vegetation is removed from land that receives little rain, plants are slow to grow back. This affects soil because it increases erosion. Urban construction: erodes the soil by wind and water. This eroded soil can enter streams causing them to fill up with sediments. This damages streams because it covers dwelling organisms and eggs, clogging the streams or reducing the downstream water quality.

Preventing Soil Erosion There are many things that can be done to prevent soil erosion. Here are a few things mentioned in the chapter: Farmers can plant shelter belts of trees, cover bare soils with decaying plants, graze animals on vegetation instead of plowing it under, or use no-till farming Plant along natural contours of the land (contour farming). Terracing can also be done to grow crops. At construction sites, cover exposed land with mulch, mats, or plastic. Spraying water on exposed land, add topsoil and plant trees. Also build retaining walls to prevent soil from eroding.

Explain why soil is important Identify human activities that lead to soil loss Describe ways to reduce soil loss