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Weathering and Its Effects

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Presentation on theme: "Weathering and Its Effects"— Presentation transcript:

1 Weathering and Its Effects
The mechanical and chemical processes that change objects on Earth’s surface over time are called weathering. Over thousands of years, weathering can break rock into smaller and smaller pieces, such as sand, silt, and clay.

2 Mechanical Weathering
When physical processes naturally break rocks into smaller pieces, mechanical weathering occurs. The chemical makeup of a rock stays the same during mechanical weathering. Mechanical weathering can be caused by ice wedging, abrasion, plants, and animals.

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4 Surface area is the amount of space on the outside of an object.
Mechanical Weathering (cont.) An example of mechanical weathering is when the intense heat of a forest fire causes nearby rocks to expand and crack. When something is broken into smaller pieces, it has a greater surface area. Surface area is the amount of space on the outside of an object.

5 Chemical Weathering Chemical weathering changes the materials that are part of a rock into new materials. These granite obelisks show how chemical weathering can affect some rock. Dr. Marli Miller/Getty Images

6 Chemical Weathering (cont.)
Water is important in chemical weathering because most substances dissolve in water. The process of dissolving breaks up the minerals in the rock into small pieces. The small pieces mix with water to form a solution and are washed away from the rock.

7 Chemical Weathering (cont.)
Acids are also agents of chemical weathering and cause more chemical weathering than pure water does.

8 The product of oxidation is called an oxide.
Chemical Weathering (cont.) Oxidation combines the element oxygen with other elements or molecules. The product of oxidation is called an oxide. When rocks that contain iron oxidize, a layer of iron oxide forms on the outside surface.

9 The environment helps determine the rate of weathering.
What affects weathering rates? The environment helps determine the rate of weathering. Mechanical weathering occurs fastest in locations that have a lot of temperature changes.

10 Chemical weathering is fastest in warm, wet places.
What affects weathering rates? Chemical weathering is fastest in warm, wet places. The type of rock being weathered also affects the rate of weathering and determines what kinds of products result.

11 Constructive processes build up features on Earth’s surface.
Reshaping Earth’s Surface A combination of constructive processes and destructive processes produce landforms. Constructive processes build up features on Earth’s surface. Destructive processes tear down features on Earth’s surface.

12 The breakdown of rock—weathering— is one type of destructive process that changes Earth’s surface.

13 Chemical weathering alters the chemical composition of rock.
A Continual Process of Change Chemical weathering alters the chemical composition of rock. Physical weathering is the breaking of rock into pieces, called sediment, without changing the chemical composition of the rock. Water, wind, and ice are agents, or causes, of weathering.

14 A Continual Process of Change (cont.)
The mineral composition of some rocks makes them less resistant than others are to weathering. The difference in the rate of weathering can produce unusual landforms.

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16 Agents of erosion include water, wind, glaciers, and gravity.
Erosion is the removal of weathered material from one location to another. Agents of erosion include water, wind, glaciers, and gravity. Factors that affect the rate of erosion include weather, climate, shape of the land, and type of rock.

17 The rate of erosion sometimes depends on the type of rock.
Erosion (cont.) The presence of plants and the way humans use the land affect the rate of erosion. The rate of erosion sometimes depends on the type of rock. Weathering breaks some types of rock into large pieces. Other rock types easily break into smaller pieces that are more easily transported.

18 Erosion (cont.) As rock fragments bump against each other during erosion, the shapes of the fragments can change.

19 Erosion (cont.) Erosion also affects the level of sorting— separating of items into groups according to one or more properties—of sediment. Sediment is often well-sorted when it has been moved a lot by wind or waves. Poorly sorted sediment often results from rapid transportation, perhaps by a storm, a flash flood, or a volcanic eruption.

20 Deposition is the laying down or settling of eroded material.

21 Deposition (cont.) As water or wind slows down, it has less energy and can hold less sediment, which can result in some of the sediment being deposited. Sediment is deposited in locations called depositional environments, such as swamps, deltas, beaches, and the ocean floor.

22 Deposition (cont.) High-energy environments, like rushing rivers and ocean shores with large waves, are those in which sediment is transported and deposited quickly. Small grains of sediment are often deposited in low-energy environments, like deep lakes, areas of slow-moving air, and swamps.

23 Landforms can have features that are clearly produced by erosion.
Interpreting Landforms Landforms can have features that are clearly produced by erosion. Different rates of erosion can create unusual landforms like tall, protruding landforms called hoodoos. Glacial erosion can produce ice-carved features in mountains.

24 Landforms created by deposition are often flat and low-lying.
Interpreting Landforms (cont.) Landforms created by deposition are often flat and low-lying. An apron of sediment, called an alluvial fan, often forms where a stream flows from a steep, narrow canyon onto a flat plain at the foot of a mountain.

25 Interpreting Landforms (cont.)
Deposition along a riverbed occurs where the speed of the water slows down and can result in a sandbar.

26 Erosion by water and wind can change the shape of landforms.
Shaping the Land with Water and Wind Water and wind are two important agents of weathering, erosion, and deposition. Erosion by water and wind can change the shape of landforms.

27 Streams are active systems that erode land and transport sediment.
Water Erosion and Deposition Streams are active systems that erode land and transport sediment. The erosion produced by a stream depends on the stream’s energy. This energy is usually greatest in steep, mountainous areas where young streams flow rapidly downhill.

28 Water Erosion and Deposition
Water from a young stream slows down as it reaches gentler slopes and is then called a mature stream. A stream moves slowly when it reaches flat land and is then called an old stream.

29 A meander is a broad, C-shaped curve in a stream.
Water Erosion and Deposition (cont.) A meander is a broad, C-shaped curve in a stream. As time passes, erosion of the outside bend of a meander, where water is flowing more quickly, occurs. Deposition occurs on the inside bend, where water flows more slowly.

30 Over time, meanders change shape due to erosion and deposition.

31 A longshore current is a current that flows parallel to the shoreline.
Water Erosion and Deposition (cont.) Waves crashing into shore erode loose sand, gravel, and rock along coastlines. A longshore current is a current that flows parallel to the shoreline. This current moves sediment and continually changes the size and shape of beaches.

32 Water erosion can also form caves, stacks, and arches.
Water Erosion and Deposition (cont.) Water erosion can also form caves, stacks, and arches.

33 Flowing water deposits sediment as the water slows down.
Water Erosion and Deposition (cont.) Flowing water deposits sediment as the water slows down. Slower-moving water deposits sediment on the inside curves of meanders. A delta is a large deposit of sediment that forms where a stream enters a large body of water.

34 Water Erosion and Deposition (cont.)
Much of the sand on most ocean beaches was originally deposited by rivers. Longshore currents transport the sand along ocean coasts and deposit it where the currents have less energy.

35 Ocean waves can erode beaches by removing sediment.
Water Erosion and Deposition (cont.) Ocean waves can erode beaches by removing sediment. To reduce erosion, people sometimes build structures such as retaining walls or groins. Reducing or removing vegetation from the land surface is one of the most common ways that surface erosion is increased.

36 A dune is a pile of wind-blown sand.
Wind Erosion and Deposition Abrasion is the grinding away of rock or other surfaces as particles carried by wind, water, or ice scrape against them. A dune is a pile of wind-blown sand. Loess is a crumbly, windblown deposit of silt and clay.

37 Wind Erosion and Deposition (cont.)
Plowed fields and dry, overgrazed pastures are two ways in which people contribute to wind erosion.

38 Mass Wasting Mass wasting is the downhill movement of a large mass of rocks or soil because of the pull of gravity. Mass wasting commonly occurs when soil on a hillside is soaked with rainwater. A landslide is the rapid downhill movement of soil, loose rocks, and boulders.

39 Two types of landslides are a rockfall and a mudslide.
Mass Wasting (cont.) Two types of landslides are a rockfall and a mudslide. Slump is a type of mass wasting where the material moves slowly, in a large mass. If the material moves too slowly to be noticeable, causing trees and other objects to lean over, the event is called creep.

40 Talus is a pile of angular rocks and sediment from a rockfall.
Mass Wasting (cont.) When material reaches a stable location, such as the base of a mountain, the material is deposited. Talus is a pile of angular rocks and sediment from a rockfall.

41 Mass Wasting (cont.) Human activity, such as removing vegetation, can affect both the severity of mass wasting and the tendency for it to occur. Landscaping or building on a slope can make the slope steeper and more likely to undergo mass wasting.

42 The two main types of glaciers are alpine glaciers and ice sheets.
Glacial Erosion and Deposition A glacier is a large mass of ice that formed on land and moves slowly across Earth’s surface. The two main types of glaciers are alpine glaciers and ice sheets. Glaciers erode Earth’s surface as they slide over it, carving the land as they move.

43 Alpine glaciers produce distinctive erosional features.

44 Sediment that was frozen in a glacier’s ice is eventually deposited in various forms.

45 Till is a mixture of various sizes of sediment deposited by a glacier.
Glacial Erosion and Deposition (cont.) Till is a mixture of various sizes of sediment deposited by a glacier. A moraine is a mound or ridge of unsorted sediment deposited by a glacier.

46 As glaciers melt, sea level rises around the world.
Glacial Erosion and Deposition (cont.) Outwash is layered sediment deposited by streams of water that flow from a melting glacier. A small change in Earth’s average temperature causes considerable melting of glaciers. As glaciers melt, sea level rises around the world.

47 Organic matter is the remains of something that was once alive.
What is soil? Soil is a mixture of weathered rock, decayed organic matter, mineral fragments, water, and air. Organic matter is the remains of something that was once alive. Decomposition is the process of changing once-living material into dark-colored organic matter.

48 The sizes of pores change with differences in particle size.
What is soil? (cont.) Soil contains gases that fill the soil pores–the small holes and spaces in soil. The sizes of pores change with differences in particle size.

49 The term inorganic describes materials that have never been alive.
Formation of Soil Inorganic matter in soil is formed by the mechanical and chemical weathering of rocks into fragments. The term inorganic describes materials that have never been alive.

50 Parent material is the starting material of soil.
Formation of Soil (cont.) Parent material is the starting material of soil. Parent material is made of the rock or sediment that weathers to form the soil.

51 The average weather of an area is its climate.
Formation of Soil (cont.) The average weather of an area is its climate. If the parent material is in a warm, wet climate, soil formation can be rapid. Topography is the shape and steepness of the landscape.

52 Formation of Soil (cont.)
The topography of an area determines what happens to water that reaches the soil surface. Water running downhill can carry soil with it, leaving some slopes bare of soil.

53 Biota is all of the organisms that live in a region.
Formation of Soil (cont.) Biota is all of the organisms that live in a region. Biota in the soil help speed up the process of soil formation in various ways. Organisms can be involved in decomposition of organic matter or form passages in soil for water to move through.

54 Rock and soil are affected by organism activity.
Mature soils develop layers as new soil forms on top of older soil.

55 Horizons As time passes, weathering is constantly acting on rock and sediment, making soil formation a constant, but slow, process. Horizons are layers of soil formed from the movement of the products of weathering.

56 Horizons (cont.) Each horizon has characteristics based on the type of materials it contains. The three horizons common to most soils are identified as A-horizon, B-horizon, and C- horizon. The top, organic layer is called the O-horizon and the unweathered, bedrock layer is the R-horizon.

57 Soil Properties and Uses

58 Some properties of soil can be determined just by observation.
Soil Properties and Uses (cont.) Some properties of soil can be determined just by observation. The amount of sand, silt, and clay in a soil can be estimated by feeling the soil. Many soil properties can be measured more accurately in a laboratory.

59 Soil Properties and Uses (cont.)
Laboratory measurements can determine exactly what is in each sample of soil. Plant growers can observe how well plants grow in the soil to get information about soil nutrients.

60 The type of soil formed depends partly on climate.


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