Section 7.1: Weathering Section 7.2: Erosion and Deposition Section 7.3: Soil Weathering, Erosion, and Soil 7

Objectives Distinguish between mechanical and chemical weathering. Describe the different factors that affect mechanical and chemical weathering. Identify variables that affect the rate of weathering. Weathering Section 7.1

Review Vocabulary acid: solution that contains hydrogen ions Weathering Weathering breaks down materials on or near Earth’s surface. Section 7.1

New Vocabulary weathering mechanical weathering frost wedging Weathering Section 7.1 exfoliation chemical weathering oxidation

Mechanical Weathering Weathering is the process in which materials on or near Earth’s surface break down and change. Mechanical weathering is a type of weathering in which rocks and minerals break down into smaller pieces. It does not change a rock’s composition. Weathering Section 7.1

Mechanical Weathering Effect of temperature Weathering Section 7.1 When water freezes, it increases in volume. If the temperature drops to the freezing point, water that has collected in the cracks of rocks or rock layers freezes, expands, and exerts pressure on the rocks, which can cause the cracks to widen slightly.

Weathering Section 7.1 Mechanical Weathering When the temperature increases, ice melts in the cracks of rocks and rock layers. The freeze-thaw cycles of water in the cracks of rocks is called frost wedging. Effect of temperature

On a small scale, plant or tree roots wedged in the cracks of rocks exert pressure as they grow and expand, which often causes the rocks to split. Effect of pressure Mechanical Weathering Weathering Section 7.1

Weathering Section 7.1 On a larger scale, when overlying rock layers are removed by processes such as erosion or even mining, the pressure on the bedrock is reduced. The bedrock surface that was buried expands, and long, curved cracks can form. Effect of pressure Mechanical Weathering

Weathering Section 7.1 Exfoliation is a mechanical weathering process in which outer rock layers are stripped away, often resulting in dome-shaped formations. Effect of pressure Mechanical Weathering

Chemical Weathering Chemical weathering is the process by which rocks and minerals undergo changes in their composition. Agents of chemical weathering include water, oxygen, carbon dioxide, and acid precipitation. Weathering Section 7.1

Chemical Weathering The composition of a rock determines the effects that chemical weathering will have on it. Weathering Section 7.1

Weathering Section 7.1 Chemical Weathering Temperature is a significant factor in chemical weathering because it influences the rate at which chemical reactions occur.

Weathering Section 7.1 Chemical Weathering Water is an important agent in chemical weathering because it can dissolve many kinds of minerals and rocks. Water serves as a medium in which chemical reactions can occur, and it can also react directly with minerals in a chemical reaction. Effect of water

Weathering Section 7.1 Chemical Weathering The chemical reaction of oxygen with other substances is called oxidation. Iron in rocks and minerals combines with atmospheric oxygen to form minerals with the oxidized form of iron. Hematite is a common example. Effect of oxygen

Weathering Section 7.1 Chemical Weathering When carbon dioxide combines with water in the atmosphere, it forms a very weak acid called carbonic acid that falls to Earth’s surface as precipitation. The slight acidity of precipitation can cause it to dissolve certain rocks, such as limestone. Effect of carbon dioxide

Weathering Section 7.1 Chemical Weathering When slightly acidic water from precipitation seeps into the ground, it combines with carbon dioxide in the soil, and becomes a stronger acid. Carbonic acid slowly reacts with minerals such as calcite in limestone to dissolve rocks. Effect of carbon dioxide

Weathering Section 7.1 Chemical Weathering Sulfur dioxide, carbon dioxide, and nitrogen oxides are released into the atmosphere by human activities. When these gases combine with water and oxygen in the atmosphere, sulfuric, carbonic, and nitric acids form and cause acid precipitation. Effect of acid precipitation

Weathering Section 7.1 Chemical Weathering Because strong acids can be harmful to many organisms and destructive to human-made structures, acid precipitation often creates problems, such as making forests more vulnerable to disease. Effect of acid precipitation

Weathering Section 7.1 Rate of Weathering The natural weathering of Earth materials occurs slowly. However, certain conditions and interactions can accelerate or slow the weathering process.

Weathering Section 7.1 Rate of Weathering The interaction between temperature and precipitation in a given climate determines the rate of weathering in a region. Effects of climate on weathering

Weathering Section 7.1 Rate of Weathering Warm, lush areas such as the tropics experience the fastest chemical weathering. Effects of climate on weathering

Weathering Section 7.1 Rate of Weathering Physical weathering can break down rocks more rapidly in cool climates. Conditions in such climates do not favor chemical weathering because cool temperatures slow or inhibit chemical reactions. Effects of climate on weathering

Weathering Section 7.1 Rate of Weathering Not all the rocks in the same climate weather at the same rate. The effects of climate on the weathering of rock also depend on the rock type and composition. Rock type and composition

Weathering Section 7.1 Rate of Weathering Mechanical weathering breaks rocks into smaller pieces. As the pieces get smaller, their surface area increases, resulting in more total surface area available for chemical weathering. Surface area

Weathering Section 7.1 Rate of Weathering The slope of a landscape helps determine the rate of weathering. Steep slopes promote erosion and continually expose less-weathered material. Topography

Objectives Describe the relationship of gravity to all agents of erosion. Contrast the features left from different types of erosion. Analyze the impact of living and nonliving things on the processes of weathering and erosion. Erosion and Deposition Section 7.2

gravity: a force of attraction between objects due to their masses Review Vocabulary Erosion transports weathered materials across Earth’s surface until they are deposited. Erosion and Deposition Section 7.2

New Vocabulary Erosion and Deposition Section 7.2 erosion deposition rill erosion gully erosion

Gravity’s Role The removal of weathered rock and soil from its original location is a process called erosion. Erosion can remove material through a number of different agents, including running water, glaciers, wind, ocean currents, and waves. Erosion and Deposition Section 7.2

Erosion and Deposition Section 7.2 Gravity’s Role After the rock and soil are transported, sometimes thousands of kilometers away from their source, they are dropped in another location in a process known as deposition.

Erosion and Deposition Section 7.2 Gravity’s Role Gravity is associated with many erosional agents because the force of gravity tends to pull all materials downslope.

Erosion and Deposition Section 7.2 Erosion by Water Stream erosion can reshape entire landscapes. Water flowing down steep slopes has additional erosive potential resulting from gravity, causing it to cut downward into the slopes, carving steep valleys and carrying away rock and soil.

Erosion and Deposition Section 7.2 Erosion by Water Rill erosion develops when running water cuts small channels into the side of a slope. When a channel becomes deep and wide, rill erosion evolves into gully erosion.

Erosion and Deposition Section 7.2 Erosion by Water Once a river enters the ocean, the current slows down, which reduces the potential of the stream to carry sediment. As a result, rivers deposit large amounts of sediment near the region where they enter the ocean. Over time, deltas form. Rivers and streams

Erosion and Deposition Section 7.2 Erosion by Water The work of ocean currents, waves, and tides carves out cliffs, arches, and other features along the continents’ edges. Wave action

Erosion and Deposition Section 7.2 Erosion by Water The constant movement of water and the availability of accumulated weathered material result in a continuous erosional process. Deposition of sand particles forms features such as beaches and sandbars; erosion removes sand from these features. Wave action

Glacial Erosion Because glaciers can move as dense, enormous rivers of slowly flowing ice, they have the capacity to carry huge rocks and piles of debris over great distances and grind the rocks beneath them into flour-sized particles. Erosion and Deposition Section 7.2

Erosion and Deposition Section 7.2 Glacial Erosion The features left in the wake of glaciers include steep U-shaped valleys and lakes.

Erosion and Deposition Section 7.2 Glacial Erosion The effects of glaciers on the landscape also include deposition. For example, soils in the northern parts of the United States are formed from material that was transported and deposited by glaciers.

Wind Erosion Wind can be a major erosional agent, especially in arid and coastal regions, which tend to have little vegetation to hold soil in place. Wind can easily pick up and move fine, dry particles. Erosion and Deposition Section 7.2

Erosion and Deposition Section 7.2 Wind Erosion The abrasive action of windblown particles can damage both natural features and human-made structures. Winds can also easily move fine-grained sediments and sand uphill.

Erosion by Living Things As plants and animals carry out their life processes, they often move Earth’s surface materials from one place to another. Erosion and Deposition Section 7.2

Objectives Describe how soil forms. Recognize soil horizons in a soil profile. Differentiate among the factors of soil formation. Soil Section 7.3 organism: anything that has or once had all the characteristics of life Review Vocabulary

Soil forms slowly as a result of mechanical and chemical processes. Soil Section 7.3 New Vocabulary soil residual soil transported soil soil profile soil horizon

Soil Formation Soil is the loose covering of weathered rock particles and decaying organic matter, called humus, overlying the bedrock on Earth’s surface, and serves as a medium for the growth of plants. Soil Section 7.3

Soil Section 7.3 Soil Formation The soil-development process often begins when weathering breaks solid bedrock into smaller pieces, which continue to undergo weathering and break down further. Soil development

Soil Section 7.3 Soil Formation Worms and other organisms help break down organic matter and add nutrients to the soil as well as creating passages for air and water. Soil development

Soil Section 7.3 Soil Layers During the process of its formation, soil develops layers. Most of the volume of soil is formed from the weathered products of a source rock, called the parent material.

Soil Layers Soil Section 7.3 A soil whose parent material is the local bedrock is called residual soil. Transported soil is soil that develops from parent material that has been moved far from its original location, usually by agents of erosion.

Soil Section 7.3 Soil Layers Soil profiles A soil profile is a vertical sequence of soil layers. New soils that have not yet developed distinct layers are called undeveloped soils. Mature soils are those that have distinct layers, sometimes after tens of thousands of years.

Soil Section 7.3 Soil Layers Soil profiles A distinct layer within a soil profile is called a soil horizon. There are typically four major soil horizons in mature soils: O, A, B, and C.

Soil Layers Soil profiles The O-horizon is the top layer of organic material and is composed of humus and leaf litter. The A-horizon is a layer of weathered rock combined with a rich concentration of dark brown organic material. Soil Section 7.3

Soil Section 7.3 Soil Layers Soil profiles The B-horizon, also known as the zone of accumulation, is a red or brown layer enriched over time by clay and minerals deposited by water flowing from above, or percolating upward from below. The C-horizon contains little or no organic matter and is often made of broken-down bedrock.

Factors of Soil Formation Five factors influence soil formation: climate, topography, parent material, biological organisms, and time. Soil Section 7.3

Factors of Soil Formation These factors combine to produce different types of soil, called soil orders, from region to region. The five factors of soil formation result in 12 different soil orders. Soil Section 7.3

Soil Section 7.3 Factors of Soil Formation Climate Climate is the most significant factor controlling the development of soils because it also affects the weathering of rocks. Temperature, wind, and the amount of rainfall determine the type of soil that can develop.

Factors of Soil Formation Topography Topography, which includes the slope and orientation of the land, affects the type of soil that forms. Soil Section 7.3

Soil Section 7.3 Factors of Soil Formation Topography In the northern hemisphere, slopes that face south receive more sunlight than other slopes, allowing more vegetation to grow.

Soil Section 7.3 Factors of Soil Formation Parent material If the soil is residual, it will have the same chemical composition as the local bedrock. If the soil is transported, the minerals in the soil are likely to be different from those in the local bedrock.

Soil Section 7.3 Factors of Soil Formation Biological organisms Organisms including fungi and bacteria, as well as plants and animals, interact with soil. Different types of biological organisms in a soil can result in different soil orders.

Time Soil Section 7.3 Factors of Soil Formation The effects of time alone can determine the characteristics of a soil. After tens of thousands of years of weathering, most of the original minerals in a soil are changed or washed away.

Visualizing Soil Orders The five factors of soil formation determine how the soil orders are distributed across the United States. Soil profiles of three soil orders from different parts of the country are shown. Each soil profile has soil horizons expressed differently. Soil Section 7.3

Soil Section 7.3 Please click the image above to view the video.

Soil Texture Soil Section 7.3 The relative proportions of particle sizes determine a soil’s texture, which affects a soil’s capacity to retain moisture and therefore its ability to support plant growth.

Soil Section 7.3 Soil Texture A soil textural triangle is used to determine a soil’s texture.

Soil Section 7.3 Soil Fertility Soil fertility is the measure of how well a soil can support the growth of plants. It is affected by topography, availability of minerals and nutrients, the number of microorganisms present, the amount of precipitation available, and the level of acidity.

Soil Section 7.3 Soil Color The minerals, organic matter, and moisture in each soil horizon determine its color. Scientists use the Munsell System of Color Notation to describe soil color in components of hue (color), value (lightness or darkness), and chroma (intensity).

Chapter Resource Menu Section Questions Chapter Assessment Questions Standardized Test Practice Earth Science Online Glencoe Earth Science Transparencies Image Bank Vocabulary Animations Click on a hyperlink to view the corresponding feature. Study Guide Weathering, Erosion, and Soil 7

Key Concepts Section 7.1 Weathering Weathering breaks down materials on or near Earth’s surface. Mechanical weathering changes a rock’s size and shape. Frost wedging and exfoliation are forms of mechanical weathering. Study Guide 7

Chemical weathering changes the composition of a rock. The rate of chemical weathering depends on the climate, rock type, surface area, and topography. Section 7.1 Weathering 7 Study Guide Key Concepts

Erosion transports weathered materials across Earth’s surface until they are deposited. The processes of erosion and deposition have shaped Earth’s landscape in many ways. Section 7.2 Erosion and Deposition 7 Study Guide Key Concepts

Gravity is the driving force behind major agents of erosion. Agents of erosion include running water, waves, glaciers, wind, and living things. Section 7.2 Erosion and Deposition 7 Study Guide Key Concepts

Key Concepts Section 7.3 Soil Soil forms slowly as a result of mechanical and chemical processes. Soil consists of weathered rock and humus. Soil is either residual or transported A typical soil profile has O-horizon, A-horizon, B-horizon, and C-horizon. Study Guide 7

Key Concepts Section 7.3 Soil Five factors influence soil formation: climate, topography, parent material, biological organisms, and time. Characteristics of soil include texture, fertility, and color. Study Guide 7

Which mineral can form as a result of the oxidation of iron at Earth’s surface? a. olivine b. quartz c. feldspar d. hematite 7.1 Section Questions Weathering, Erosion, and Soil 7

In which climate is mechanical weathering most rapid? a. warm and wet b. warm and dry c. cool and wet d. cool and dry 7.1 Section Questions Weathering, Erosion, and Soil 7

What effects do mechanical and chemical weathering have on the rock at Earth’s surface? 7.1 Section Questions Weathering, Erosion, and Soil 7

Possible answer: Mechanical weathering breaks rock apart but does not change its composition. Chemical weathering dissolves some rock and also causes some new minerals, such as iron oxides and clays, to form. 7.1 Section Questions Weathering, Erosion, and Soil 7

Erosion is the picking up and moving of rock or soil from a location. a. true b. false 7.2 Section Questions Weathering, Erosion, and Soil 7

Which feature forms as a result of deposition of sediment at a river’s mouth? a. a canyon b. a delta c. a channel d. a barrier island 7.2 Section Questions Weathering, Erosion, and Soil 7

How does gravity cause erosion on Earth? Possible answer: Gravity causes erosion directly when landslides occur. It causes erosion indirectly by providing the driving force that causes streams and glaciers to flow. 7.2 Section Questions Weathering, Erosion, and Soil 7

Which soil horizon is most similar to the parent material from which the soil formed? a. O-horizon b. A-horizon c. B-horizon d. C-horizon 7.3 Section Questions Weathering, Erosion, and Soil 7

What soil nutrient is replenished by planting legumes? a. phosphate b. nitrate c. potassium d. manganese 7.3 Section Questions Weathering, Erosion, and Soil 7

In which climate would intensely weathered soils consisting only of insoluble materials form? a. a dry polar climate b. a hot desert climate c. a cool temperate climate d. a wet tropical climate 7.3 Section Questions Weathering, Erosion, and Soil 7

Which process is considered to be chemical weathering? a. frost wedging b. exfoliation c. oxidation d. burrowing Chapter Assessment Questions Weathering, Erosion, and Soil 7

Carbon dioxide in the air reacts with rainwater and surface water on Earth. Which acid is a product of this reaction? a. hydrochloric b. sulfuric c. carbonic d. nitric Chapter Assessment Questions Weathering, Erosion, and Soil 7

Which feature forms as a result of erosion by glaciers? a. a field without topsoil b. a U-shaped valley c. a rill and gully system d. a scarp on a hillside Chapter Assessment Questions Weathering, Erosion, and Soil 7

In which geologic setting is a thick, well-developed soil most likely to form? a. a mountain slope b. a valley floor c. a river bar d. a sandy beach Chapter Assessment Questions Weathering, Erosion, and Soil 7

How do organisms affect the development of soil? Chapter Assessment Questions Weathering, Erosion, and Soil 7 Possible answer: Organisms affect the development of soil in several ways. Plants contribute organic matter to soil. Microorganisms decompose organic matter and change it into humus. Some animals, such as earthworms, aerate soil by burrowing in it.

In which climate is chemical weathering most rapid? a. warm and wet b. warm and dry c. cool and wet d. cool and dry Standardized Test Practice Weathering, Erosion, and Soil 7

A soil consists of 20 percent clay, 40 percent silt, and 40 percent sand. How is this soil classified? a. clay b. loam c. clay loam d. silt loam Standardized Test Practice Weathering, Erosion, and Soil 7

What soil horizon is called the zone of accumulation because clays and some other minerals accumulate there? a. O-horizon b. A-horizon c. B-horizon d. C-horizon Standardized Test Practice Weathering, Erosion, and Soil 7

Standardized Test Practice Weathering, Erosion, and Soil 7 In which setting would erosion by wind normally be highest? a. a prairie b. a forest c. a desert d. a swamp

Which landscape features form as a result of erosion by flowing water? Standardized Test Practice Weathering, Erosion, and Soil 7 Possible answer: Small features that result from erosion by flowing water include rills and gullies. Large features include river channels and canyons. Through very long periods of time, flowing water can sculpt entire landscapes.

Weathering, Erosion, and Soil 7 Glencoe Earth Science Transparencies

Weathering, Erosion, and Soil 7 Image Bank

Section 7.1 Vocabulary weathering mechanical weathering frost wedging exfoliation chemical weathering oxidation Weathering, Erosion, and Soil 7

Section 7.2 Vocabulary Weathering, Erosion, and Soil 7 erosion deposition rill erosion gully erosion

Section 7.3 Vocabulary soil residual soil transported soil soil profile soil horizon Weathering, Erosion, and Soil 7

Visualizing Soil Orders Animations 7