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Chapter Presentation Visual Concepts Transparencies Standardized Test Prep Brain Food Video Quiz

Weathering and Erosion Table of Contents Section 1 Weathering Processes Section 2 Rates of Weathering Section 3 Soil Section 4 Erosion

Section 1 Weathering Processes Objectives Identify three agents of mechanical weathering. Compare mechanical and chemical weathering processes. Describe four chemical reactions that decompose rock.

Section 1 Weathering Processes Weathering Processes weathering the natural process by which atmospheric and environmental agents, such as wind, rain, and temperature changes, disintegrate and decompose There are two main types of weathering processes mechanical weathering and chemical weathering. Each type of weathering has different effects on rock.

Section 1 Weathering Processes Mechanical Weathering mechanical weathering the process by which rocks break down into smaller pieces by physical means Mechanical weathering is strictly a physical process and does not change the composition of the rock. Common agents of mechanical weathering are ice, plants and animals, gravity, running water, and wind. Physical changes within the rock itself affect mechanical weathering.

Section 1 Weathering Processes Mechanical Weathering, continued Ice Wedging A type of mechanical weathering that occurs in cold climates is called ice wedging. Ice wedging occurs when water seeps into the cracks in rock and freezes. When the water freezes, its volume increases by about 10% and creates pressure on the surrounding rock. This process eventually splits the rock apart.

Section 1 Weathering Processes Mechanical Weathering, continued Abrasion abrasion the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles Abrasion is caused by gravity, running water, and wind. Wind is another agent of abrasion.

Section 1 Weathering Processes Reading Check Describe two types of mechanical weathering.

Section 1 Weathering Processes Reading Check Describe two types of mechanical weathering. Two types of mechanical weathering are ice wedging and abrasion. Ice wedging is caused by water that seeps into cracks in rock and freezes. When water freezes, it expands and creates pressure on the rock, which widens and deepens cracks. Abrasion is the grinding away of rock surfaces by other rocks or sand particles. Abrasive agents may be carried by gravity, water, and wind.

Section 1 Weathering Processes Mechanical Weathering, continued Organic Activity Plants and animals are important agents of mechanical weathering. As plants grow, the roots grow and expand to create pressure that wedge rock apart. Earthworms and other animals that move soil expose new rock surfaces to both mechanical and chemical weathering.

Section 1 Weathering Processes Chemical Weathering chemical weathering the process by which rocks break down as a result of chemical reactions Chemical reactions commonly occur between rock, water, carbon dioxide, oxygen, and acids. Bases can also chemically weather rock. Chemical weathering changes both the composition and physical appearance of the rock.

Section 1 Weathering Processes Chemical Weathering, continued Oxidation oxidation a reaction that moves one or more electrons from a substance such that the substance s valence or oxidation state increases; in geology, the process by which an element combines with oxygen Oxidation commonly occurs in rock that has ironbearing minerals, such as hematite and magnetite.

Section 1 Weathering Processes Chemical Weathering, continued Oxidation, continued Iron, Fe, in rocks and soil combines quickly with oxygen, O 2, that is dissolved in water to form rust, or iron oxide, Fe 2 O 3. 4Fe + 3O 2 2Fe 2 O 3 The red color of much of the soil in the southeastern United States is due to mainly the presence of iron oxide produced by oxidation.

Section 1 Weathering Processes Reading Check Describe two effects of chemical weathering.

Section 1 Weathering Processes Reading Check Describe two effects of chemical weathering. Two effects of chemical weathering are changes in the chemical composition and changes in the physical appearance of a rock.

Section 1 Weathering Processes Chemical Weathering, continued Hydrolysis hydrolysis a chemical reaction between water and another substance to form two or more new substances Water plays a crucial role in chemical weathering. Minerals that are affected by hydrolysis often dissolve in water. Water can then carry the dissolved minerals to lower layers of rock in a process called leaching.

Section 1 Weathering Processes Chemical Weathering, continued The image below shows how water plays a crucial role in chemical weathering.

Section 1 Weathering Processes Chemical Weathering, continued Carbonation carbonation the conversion of a compound into a carbonate When carbon dioxide, CO 2, from the air dissolves in water, H 2 O, a weak acid called carbonic acid, H 2 CO 3, forms. H 2 O + CO 2 H 2 CO 3 Carbonic acid has a higher concentration of hydronium ions than pure water does, which speeds up the process of hydrolysis.

Section 1 Weathering Processes Chemical Weathering, continued Organic Acids Acids are produced naturally by certain living organisms. Lichens and mosses grow on rocks and produce weak acids that can weather the surface of the rock. The acids seep into the rock and produce cracks that eventually cause the rock to break apart.

Section 1 Weathering Processes Chemical Weathering, continued Acid Precipitation acid precipitation precipitation, such as rain, sleet, or snow, that contains a high concentration of acids, often because of the pollution of the atmosphere Acid precipitation weathers rock faster than ordinary precipitation does. Rainwater is slightly acidic because it combines with small amounts of carbon dioxide.

Section 1 Weathering Processes Chemical Weathering, continued Acid Precipitation, continued But when fossil fuels, especially coal, are burned, nitrogen oxides and sulfur dioxides are released into the air. These compounds combine with water in the atmosphere to produce nitric acid, nitrous acid, or sulfuric acid. The occurrence of acid precipitation has been greatly reduced since power plants have installed scrubbers that remove much of the sulfur dioxide before it can be released.

Section 1 Weathering Processes Ice Wedging

Section 2 Rates of Weathering Objectives Explain how rock composition affects the rate of weathering. Discuss how surface area affects the rate at which rock weathers. Describe the effects of climate and topography on the rate of weathering.

Section 2 Rates of Weathering Rates of Weathering The processes of mechanical and chemical weathering generally work very slowly. The rate at which rock weathers depends on a number of factors, including rock composition, climate, and topography.

Section 2 Rates of Weathering Differential Weathering differential weathering the process by which softer, less weather resistant rocks wear away at a faster rate than harder, more weather resistant rocks do When igneous rocks that are rich in the mineral quartz are exposed on Earth s surface, they remain basically unchanged, even after all of the surrounding sedimentary rock has weathered away. They remain unchanged because the chemical composition and crystal structure of quartz make quartz resistant to chemical weathering.

Section 2 Rates of Weathering Rock Composition Limestone and other sedimentary rocks that contain calcite are weathered most rapidly. They weather rapidly because they commonly undergo carbonation. Other sedimentary rocks are affected mainly by mechanical weathering processes. The rates at which these rocks weather depend mostly on the material that holds the sediment grains together. For example, shales and sandstones that are not firmly cemented together gradually break up to become clay and sand particles.

Section 2 Rates of Weathering Amount of Exposure Surface Area Both chemical and mechanical weathering may split rock into a number of smaller rocks. The part of a rock that is exposed to air, water, and other agents of weathering is called the rock s surface area. As a rock breaks into smaller pieces, the surface area that is exposed increases.

Section 2 Rates of Weathering Amount of Exposure, continued The image below shows the ratio of total surface area to volume.

Section 2 Rates of Weathering Amount of Exposure, continued Fractures and Joints Most rocks on Earth s surface contain natural fractures and joints. These structures are natural zones of weakness within the rock. Fractures and joints increase the surface area of a rock and allow weathering to take place more rapidly. They also form natural channels through which water flows.

Section 2 Rates of Weathering Reading Check How do fractures and joints affect surface area?

Section 2 Rates of Weathering Reading Check How do fractures and joints affect surface area? Fractures and joints in a rock increase surface area and allow weathering to occur more rapidly.

Section 2 Rates of Weathering Climate In general, climates that have alternating periods of hot and cold weather allow the fastest rates of weathering. In warm, humid climates, chemical weathering is also fairly rapid. The constant moisture is highly destructive to exposed surfaces. The slowest rates of weathering occur in hot, dry climates. The lack of water limits many weathering processes, such as carbonation and ice wedging. Weathering is also slow in very cold climates.

Section 2 Rates of Weathering Topography Because temperatures are generally cold at high elevations, ice wedging is more common at high elevations than at low elevations. On steep slopes, such as mountainsides, weathered rock fragments are pulled downhill by gravity and washed out by heavy rains. As a result of the removal of these surface rocks, new surfaces of the mountain are continually exposed to weathering.

Section 2 Rates of Weathering Human Activities Mining and construction often expose rock surfaces to agents of weathering. Mining also often exposes rock to strong acids and other chemical compounds that are used in mining processes. Recreational activities such as hiking or riding allterrain vehicles can also speed up weathering by exposing new rock surfaces. Rock that is disturbed or broken by human activities weathers more rapidly than undisturbed rock does.

Section 2 Rates of Weathering Plant and Animal Activities Rock that is disturbed or broken by plants or animals also weathers more rapidly than undisturbed rock does. The roots of plants and trees often break apart rock. Burrowing animals dig holes into rock and soil. Some biological wastes of animals can cause chemical weathering.

Section 2 Rates of Weathering Dissolving Process

Section 3 Soil Objectives Summarize how soil forms. Explain how the composition of parent rock affects soil composition. Describe the characteristic layers of mature residual soils. Predict the type of soil that will form in arctic and tropical climates.

Section 3 Soil Soil soil a loose mixture of rock fragments and organic material that can support the growth of vegetation One result of weathering is the formation of regolith, a layer of weathered rock fragments that covers much of Earth s surface. Bedrock is the solid, unweathered rock that lies beneath the regolith.

Section 3 Soil Characteristics of Soil The characteristics of soil depend mainly on the rock from which the soil was weathered, which is called the soil s parent rock. Soil Composition Soil composition refers to the materials of which it is made. The color of soil is related to the composition of the soil. Soil moisture can also affect color.

Section 3 Soil Characteristics of Soil, continued Soil Texture Rock material in soil consists of three main types: clay, silt, and sand. Clay particles have a diameter of less than 0.004 mm. Silt particles have a diameter from 0.004 to 0.06 mm. Sand particles have diameters from 0.06 to 2mm. The proportion of clay, silt, and sand in soil depends on the soil s parent rock.

Section 3 Soil Soil Profile soil profile a vertical section of soil that shows the layers of horizons horizon a horizontal layer of soil that can be distinguished from the layers above and below it; also a boundary between two rock layers that have different physical properties Transported soils are commonly deposited in unsorted masses. However, residual soils commonly develop distinct layers over time.

Section 3 Soil Soil Profile, continued humus dark, organic material formed in soil from the decayed remains of plants and animals Residual soils generally consist of three main horizons. The A horizon, or topsoil, is a mixture of organic materials and small rock particles. The B horizon or subsoil, contains the minerals leached from the topsoil, clay, and sometimes, humus. The C horizon consists of partially-weathered bedrock.

Section 3 Soil Soil Profile, continued The image below shows the soil horizons of residual soils.

Section 3 Soil Soil and Climate Climate is one of the most important factors that influences soil formation. Climate determines the weathering processes that occur in a region. These weathering processes, in turn, help determine the composition of soil.

Section 3 Soil Soil and Climate, continued Tropical Soils In humid tropical climates, where much rain falls and where temperatures are high, chemical weathering causes thick soils to develop rapidly. Leached minerals from the A horizon sometimes collect in the B horizon. Heavy rains, which are common in tropical climates, cause a lot of leaching of the topsoil, and thus keep the A horizon thin. A thin layer of humus usually covers the B horizon.

Section 3 Soil Soil and Climate, continued Temperate Soils In temperate climates, where temperatures range between cool and warm and here rainfall is not excessive, both mechanical and chemical weathering occur. All three soil horizons in temperate soils may reach a thickness of several meters.

Section 3 Soil Reading Check Compare the formation of tropical soils and temperate soils.

Section 3 Soil Reading Check Compare the formation of tropical soils and temperate soils. Large amounts of rainfall and high temperatures cause thick soils to form in both tropical and temperate climates. Tropical soils have thin A horizons because of the continuous leaching of topsoil. Temperate soils have three thick layers, because leaching of the A horizon in temperate climates is much less than leaching of the A horizon in tropical climates.

Section 3 Soil Soil and Climate, continued Desert and Arctic Soils In desert and arctic climates, rainfall is minimal and chemical weathering occurs slowly. As a result, the soil is thin and consists mostly of regolith evidence that soil in these areas form mainly by mechanical weathering. Desert and arctic climates are also often too warm or too cold to sustain life, so their soils have little humus.

Section 3 Soil Soil and Climate, continued Soil and Topography Because rainwater runs down slopes, much of the topsoil of the slope washes away. Therefore, the soil at the top and bottom of a slope tends to be thicker than the soil on the slope. Topsoil that remains on a slope is often too thin to support dense plant growth.

Section 3 Soil Soils and the Effects of Climate

Section 4 Erosion Objectives Define erosion, and list four agents of erosion. Identify four farming methods that conserve soil. Discuss two ways gravity contributes to erosion. Describe the three major landforms shaped by weathering and erosion.

Section 4 Erosion Erosion erosion a process in which the materials of Earth s surface are loosened, dissolved, or worn away and transported from one place to another by a natural agent, such as wind, water, ice, or gravity When rock weathers, the resulting rock particles do not always stay near the parent rock. Various forces may move weathered fragments of rock away from where the weathering occurred.

Section 4 Erosion Soil Erosion Ordinarily, new soil forms about as fast as existing soil erodes. Some farming and ranching practices increase soil erosion. Soil erosion is considered by some scientists to be the greatest environmental problem that faces the world today. This erosion prevents some countries from growing the crops needed to prevent widespread famine.

Section 4 Erosion Soil Erosion, continued Gullying and Sheet Erosion One farming technique that can accelerate soil erosion is the plowing of furrows, or long, narrow rows. As soil is washed away with each rainfall, a furrow becomes larger and forms a small gully. Eventually land that is plowed in this way can become covered with deep gullies. This type of accelerated soil erosion is called gullying.

Section 4 Erosion Soil Erosion, continued Gullying and Sheet Erosion, continued sheet erosion the process by which water flows over a layer of soil and removes the topsoil Another type of soil erosion strips away parallel layers of top soil. Sheet erosion may occur where continuous rainfall washes away layers of the topsoil. Wind also can cause sheet erosion during unusually dry periods.

Section 4 Erosion Soil Erosion, continued The image below shows a map of soil vulnerability worldwide to erosion by water.

Section 4 Erosion Reading Check Describe one way a dust storm may form, and explain how a dust storm can affect the fertility of land.

Section 4 Erosion Reading Check Describe one way a dust storm may form, and explain how a dust storm can affect the fertility of land. Dust storms may form during droughts when the soil is made dry and loose by lack of moisture and windcaused sheet erosion carries it away in clouds of dust. If all of the topsoil is removed, the remaining subsoil will not contain enough nutrients to raise crops.

Section 4 Erosion Soil Erosion, continued Results of Soil Erosion Constant erosion reduces the fertility of the soil be removing the A horizon, which contains the fertile humus. The B horizon, which does not contain much organic matter, is difficult to farm because it is much less fertile than the A horizon. Without plants, the B horizon has nothing to protect it from further erosion. So, within a few years, all the soil layers could be removed by continuous erosion.

Section 4 Erosion Soil Conservation Certain farming and grazing techniques and construction projects can also increase the rate of erosion. This land clearing removes protective ground cover plants and accelerates topsoil erosions. But rapid, destructive soil erosion can be prevented by soil conservation methods.

Section 4 Erosion Soil Conservation, continued Contour Plowing Farmers in countries around the world use planting techniques to reduce soil erosion. In one method, called contour plowing, soil is plowed in curved bands that follow the contour, or shape of the land. This method of planting prevents water from flowing directly down slopes, so the method prevents gullying.

Contour Plowing

Section 4 Erosion Soil Conservation, continued Strip-Cropping In strip-cropping, crops are planted in alternating bands. The cover crop protects the soil by slowing the runoff of rainwater. Strip-cropping is often combined with contour plowing. The combination of these two methods can reduce soil erosion by 75%.

Section 4 Erosion Soil Conservation, continued Terracing The construction of steplike ridges that follow the contours of a sloped field is called terracing. Terraces, especially those used for growing rice in Asia, prevent or slow the downslope movement of water and thus prevent rapid erosion.

Section 4 Erosion Soil Conservation, continued Crop Rotation In crop rotation, farmers plant one type of crop one year and a different type of crop the next. For example, crops that expose the soil to the full effects of erosion may be planted one year, and a cover crop will be planted the next year. Crop rotation stops erosion in its early stages, which allows small gullies that formed during one growing season to fill with soil during the next one.

Section 4 Erosion Gravity and Erosion mass movement the movement of a large mass of sediment or a section of land down a slope Gravity causes rock fragments to move down inclines. Some mass movements occur rapidly, and others occur very slowly.

Section 4 Erosion Gravity and Erosion, continued Rockfalls and Landslides The most dramatic and destructive mass movements occur rapidly. The fall of rock from a steep cliff is called a rockfall. A rockfall is the fastest kind of mass movement. When masses of loose rock combined with soil suddenly fall down a slope, the event is called a landslide. Heavy rainfall, spring thaws, volcanic eruptions, and earthquakes can trigger landslides.

Section 4 Erosion Reading Check What is the difference between a rockfall and a landslide?

Section 4 Erosion Reading Check What is the difference between a rockfall and a landslide? Landslides are masses of loose rock combined with soil that suddenly fall down a slope. A rockfall consists of rock falling from a steep cliff.

Section 4 Erosion Gravity and Erosion, continued Mudflows and Slumps The rapid movement of a large amount of mud creates a mudflow. Mudflows occur in dry, mountainous regions during sudden, heavy rainfall or as a result of volcanic eruptions. Mud churns and tumbles as it moves down slopes and through valleys, and it frequently spreads out in a large fan shape at the base of the slope.

Section 4 Erosion Gravity and Erosion, continued Mudflows and Slumps, continued Sometimes, a large block of soil and rock becomes unstable and moves downhill in one piece. The block of soil then slides along the curved slope of the surface. This type of movement is called a slump. Slumping occurs along very steep slopes. Saturation by water and loss of friction within underlying rock causes loose soil to slip downhill over the solid rock.

Section 4 Erosion Gravity and Erosion, continued Solifluction solifluction the slow, downslope flow of soil saturated with water in areas surrounding glaciers at high elevations Solifluction occurs in arctic and mountainous climates where the subsoil is permanently frozen. In the spring and summer, only the top layer of soil thaws. Solifluction can also occur in warmer regions, where the subsoil consists of hard clay.

Section 4 Erosion Gravity and Erosion, continued Creep creep the slow downhill movement of weathered rock material Soil creep moves the most soil of all types of mass movements. But creep may go unnoticed unless buildings, fences, or other surface objects move along with the soil. Many factors contribute to soil creep.

Section 4 Erosion Erosion and Landforms landforms a physical feature of Earth s surface There are three major landforms that are shaped by weathering and erosion mountains, plains, and plateaus. Minor landforms include hills, valleys, and dunes. All landforms are subject to two opposing processes. One process bends, breaks and lifts Earth s crust and thus creates elevated, or uplifted, landforms. The other process is weathering and erosion, which wears down land surfaces.

Section 4 Erosion Erosion and Landforms, continued Erosion of Mountains During the early stages in the history of a mountain, the mountain undergoes uplift. When the forces stop uplifting the mountain, weathering and erosion wear down the rugged peaks to rounded peaks and gentle slopes. Over millions of years, mountains that are not being uplifted become low, featureless surfaces. These areas are called peneplains, which means almost flat.

Section 4 Erosion Reading Check Describe how a mountain changes after it is no longer uplifted.

Section 4 Erosion Reading Check Describe how a mountain changes after it is no longer uplifted. When a mountain is no longer being uplifted, weathering and erosion wear down its jagged peaks to low, featureless surfaces called peneplains.

Section 4 Erosion Erosion and Landforms, continued Erosion of Plains and Plateaus A plain is a relatively flat landform near sea level. A plateau is a broad, flat landform that has a high elevation. A plateau is subject to much more erosion than a plain. The effect of weathering and erosion on a plateau depends on the climate and the composition and structure of the rock.

Section 4 Erosion Erosion and Landforms, continued Erosion of Plains and Plateaus, continued As a plateau ages, erosion may dissect the plateau into smaller, tablelike areas called mesas. Mesas ultimately erode to small, narrow-topped formations called buttes.

Mesas

Buttes

Monument Valley, AZ

Section 4 Erosion Mass Movement and Angle of Repose

Weathering and Erosion Brain Food Video Quiz

Maps in Action Maps in Action Soil Map of North Carolina

Standardized Test Prep Multiple Choice 1. The processes of physical weathering and erosion shape Earth s landforms by A. expanding the elevation of Earth s surface B. decreasing the elevation of Earth's surface C. changing the composition of Earth s surface D. bending rock layers near Earth s surface

Standardized Test Prep Multiple Choice, continued 1. The processes of physical weathering and erosion shape Earth s landforms by A. expanding the elevation of Earth s surface B. decreasing the elevation of Earth's surface C. changing the composition of Earth s surface D. bending rock layers near Earth s surface

Standardized Test Prep Multiple Choice, continued 2. Which of the following rocks is most likely to weather quickly? F. a buried rock in a mountain G. an exposed rock on a plain H. a buried rock in a desert I. an exposed rock on a slope

Standardized Test Prep Multiple Choice, continued 3. The red color of rocks and soil containing iron-rich minerals is caused by A. chemical weathering B. mechanical weathering C. abrasion D. erosion

Standardized Test Prep Multiple Choice, continued 4. In which of the following climates does chemical weathering generally occur most rapidly? F. cold, wet climates G. cold, dry climates H. warm, humid climates I. warm, dry climates

Standardized Test Prep Multiple Choice, continued 5. Which of the following has the greatest impact on soil composition? A. activity of plants and animals B. characteristics of the parent rock C. amount of precipitation D. shape of the land

Standardized Test Prep Short Response, continued 6. In what type of decomposition reaction do hydrogen ions from water displace elements in a mineral?

Standardized Test Prep Short Response, continued 6. In what type of decomposition reaction do hydrogen ions from water displace elements in a mineral? hydrolysis

Standardized Test Prep Short Response, continued 7. Sand carried by wind is responsible for what type of mechanical weathering?

Standardized Test Prep Short Response, continued 7. Sand carried by wind is responsible for what type of mechanical weathering? abrasion

Standardized Test Prep Reading Skills Read the passage below. Then, answer questions 8 10. How Rock Becomes Soil Earthworms are crucial for forming soil. As they search for food by digging tunnels, they expose rocks and minerals to the effects of weathering. Over time, this process creates new soil. Worms are not the only living things that help create soil. Plants also play a part in the weathering process. As the roots of plants grow and seek out water and nutrients, they help break large rock fragments into smaller ones. Have you ever seen a plant growing in a sidewalk? As the plant grows, its roots spread into tiny cracks in the sidewalk. These roots apply pressure to the cracks, and over time, the cracks become larger. As the plants make the cracks larger, ice wedging can occur more readily. As the cracks expand, more water can flow into them. When the water freezes, it expands and presses against the walls of the crack, which makes the crack larger. Over time, the weathering caused by water, plants, and worms helps break down rock to form soil.

Standardized Test Prep Reading Skills, continued 8. Which of the following statements can be inferred from the passage? A. Weathering can occur only when water freezes in cracks in rocks. B. Only large plants have roots that are powerful enough to increase the rate of weathering. C. Local biological activity may increase the rate of weathering in a given area. D. Plant roots often prevents weathering by filling cracks and keeping water out of cracks.

Standardized Test Prep Reading Skills, continued 9. Ice wedging, as described in the passage, is an example of which of the following? F. oxidation G. mechanical weathering H. chemical weathering I. hydrolysis

Standardized Test Prep Reading Skills, continued 10.What are some ways not mentioned in the passage in which the activity of biological organisms may increase weathering?

Standardized Test Prep Reading Skills, continued 10.What are some ways not mentioned in the passage in which the activity of biological organisms may increase weathering? Answers should include: almost any activity initiated by a living organism that exposes rock and soil to wind or water would be an acceptable answer; construction by humans breaks up rocks and creates quarries, which contribute to weathering; tunneling animals, other than worms, churn and expose rocks in soil to the surface; rotting vegetation and animal waste may release acids that can help destroy rocks when the acids are mixed with groundwater.

Standardized Test Prep Interpreting Graphics Use the diagram below to answer questions 11 and 12. The diagram shows the soil profile of a mature soil.

Standardized Test Prep Interpreting Graphics, continued 11.Which of the layers in the soil profile above contains the greatest number of soil organisms? A. layer A B. layer B C. layer C D. layer D

Standardized Test Prep Interpreting Graphics, continued 12.Which two layers in the soil profile above are the least likely to contain the dark, organic material humus. F. layers A and B G. layers B and C H. layers C and D I. layers A and D

Standardized Test Prep Interpreting Graphics Use the diagram of stone blocks to answer question 13.

Standardized Test Prep Interpreting Graphics, continued 13. If the blocks shown in diagrams A, B, and C above contain identical volumes and are made of the same types of minerals, will they weather at the same rate? Explain your answer. Answers should include: the eight small blocks in part C will weather most rapidly; students should relate the rate of weathering to the amount of exposed surface area available; students should examine the diagram and consider that the total surface area of each rectangular solid, or cube, is equal to the sum of the areas of each of the cube s six sides. The block shown in figure A has far less exposed surface than the blocks shown in figures B or C. If all conditions are equal, the more surface area that is available to experience weathering, the faster weathering will occur; even though the figures show the same volume and type of rock, the blocks of figure C would weather at the fastest rate due to their larger total surface area. The blocks of figure A would weather at the slowest rate.

Chemical Weathering

Surface Area

Soil Horizons of Residual Soils

Soil Erosion Vulnerability Map

Soil Map of North Carolina