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23.2 Weathering and Mass Movement Incredible rock formations called hoodoos can be seen at Bryce Canyon National Park in Utah.

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Presentation on theme: "23.2 Weathering and Mass Movement Incredible rock formations called hoodoos can be seen at Bryce Canyon National Park in Utah."— Presentation transcript:

1 23.2 Weathering and Mass Movement Incredible rock formations called hoodoos can be seen at Bryce Canyon National Park in Utah.

2 23.2 Weathering and Mass Movement Erosion What are the agents of erosion? Erosion acts through weathering, the force of gravity, and through the movement of streams, groundwater, glaciers, wind, and waves.

3 23.2 Weathering and Mass Movement Erosion is the process that wears down and carries away rock and soil. Erosion is the destructive process that has shaped Earth’s surface over hundreds of millions of years. The end product of erosion is sediment. Erosion

4 23.2 Weathering and Mass Movement Weathering What causes mechanical and chemical weathering? Weathering is the process by which rocks are chemically altered or physically broken down into fragments at or near Earth’s surface. There are two forms of weathering: mechanical and chemical. They cause rocks to disintegrate or decompose.

5 23.2 Weathering and Mass Movement Mechanical Weathering Mechanical weathering is the process of physically breaking rock into smaller fragments. Mechanical weathering occurs through frost wedging, abrasion, growth of plant roots, and other processes. Weathering

6 23.2 Weathering and Mass Movement Frost wedging occurs when water freezes to form ice and the water expands. The expansion pries open cracks. Frost wedging is an important cause of weathering in mountains, where water often freezes at night and melts during the day. Weathering

7 23.2 Weathering and Mass Movement When water expands to form ice, it can pry open cracks in rock. This is called frost wedging. Weathering

8 23.2 Weathering and Mass Movement Abrasion is a form of mechanical weathering that occurs when rocks scrape or grind against one another. For example, abrasion occurs when sand carried by water or wind causes bits of rock to break off as if they were being sandblasted. Weathering

9 23.2 Weathering and Mass Movement Mechanical weathering also occurs in other ways. Plant roots can grow into cracks in a rock. Roots exert a powerful force that can slowly pry the rock apart. Erosion removes material from the surface of a mass of rock, reducing pressure on the rock that remains. The rock expands, causing the outside of the rock to crack and flake off. Weathering

10 23.2 Weathering and Mass Movement Chemical Weathering Chemical weathering is a process in which rock is broken down by chemical reactions. Chemical reactions dissolve the minerals making up rock or change them into new minerals. Eventually, the rock crumbles and disintegrates. Weathering

11 23.2 Weathering and Mass Movement Water is the main agent of chemical weathering. Water is an effective solvent. All minerals dissolve in water, though most do so very slowly. Chemical weathering also occurs because rain is slightly acidic. Weathering

12 23.2 Weathering and Mass Movement A.One form of chemical weathering occurs through oxidation. Iron-rich minerals become rusted like this old bicycle. Weathering

13 23.2 Weathering and Mass Movement B.Chemical weathering also occurs when rainwater dissolves or reacts with the minerals in rocks, as with this statue of a lion. Weathering

14 23.2 Weathering and Mass Movement One type of chemical weathering, the rusting of minerals that are rich in iron, involves oxidation. Weathering

15 23.2 Weathering and Mass Movement Rates of Weathering What factors affect the rate at which rocks weather? The rate at which mechanical and chemical weathering take place depends on three main factors: temperature, the availability of water, and the type of rock.

16 23.2 Weathering and Mass Movement Chemical weathering occurs more rapidly in places with high temperatures and abundant rainfall. These conditions generally speed up chemical reactions. Mechanical weathering occurs faster in places where temperature conditions frequently alternate between freezing and thawing. Rates of Weathering

17 23.2 Weathering and Mass Movement Some rocks, such as limestone and marble, undergo rapid chemical weathering. These rocks are composed primarily of calcite, a mineral that reacts readily with carbonic acid. Rates of Weathering

18 23.2 Weathering and Mass Movement Different rocks weather at different rates. Even though the slate tombstone is older, it is much less weathered than the marble one (left). Rates of Weathering

19 23.2 Weathering and Mass Movement Mass Movement What force causes mass movement? Through the process of mass movement, gravity moves loose material down a slope.

20 23.2 Weathering and Mass Movement Once weathering loosens particles of rock, the particles, or sediment, do not stay in the same place. Mass movement is the downward movement of rock and soil due to gravity. Mass Movement

21 23.2 Weathering and Mass Movement Landslides The rapid movement of large amounts of rock and soil is a landslide. Landslides often occur after heavy rains or after earthquakes loosen materials on a steep slope. Mass Movement

22 23.2 Weathering and Mass Movement Mudflows Rapid mass movements of soil and other sediment mixed with water are called mudflows. Mudflows tend to occur in areas where fine sediment has collected in thick layers. When it rains, water loosens the sediment and increases its weight. Mass Movement

23 23.2 Weathering and Mass Movement Creep Creep occurs when soil gradually moves down a slope. Creep often occurs because of the formation of ice. Each time the ground freezes, the soil expands outward. Creep happens so slowly that it’s hard to notice. Mass Movement

24 23.2 Weathering and Mass Movement Creep can be caused by the alternate freezing and thawing of water in soil. Slumping often occurs when soil that is rich in clay is soaked by water. Mass Movement

25 23.2 Weathering and Mass Movement Slumping Slumping occurs when weak layers of soil or rock suddenly move downslope as a single unit. Gravity acting on water-saturated soil and rock causes slumping. Slumping often leaves a curved scar. Mass Movement

26 23.2 Weathering and Mass Movement Assessment Questions 1.Which of these factors tends to increase the rate of chemical weathering? a.freezing temperatures b.strong winds c.abundant rainfall d.presence of minerals such as quartz

27 23.2 Weathering and Mass Movement Assessment Questions 1.Which of these factors tends to increase the rate of chemical weathering? a.freezing temperatures b.strong winds c.abundant rainfall d.presence of minerals such as quartz ANS:C

28 23.2 Weathering and Mass Movement Assessment Questions 2.Which type of mass movement involves the gradual movement of soil down a slope? a.landslides b.mudflows c.creeps d.lumping

29 23.2 Weathering and Mass Movement Assessment Questions 2.Which type of mass movement involves the gradual movement of soil down a slope? a.landslides b.mudflows c.creeps d.lumping ANS:C

30 23.2 Weathering and Mass Movement Assessment Questions 1.Erosion breaks rocks down by two processes: mechanical weathering and chemical weathering. True False

31 23.2 Weathering and Mass Movement Assessment Questions 1.Erosion breaks rocks down by two processes: mechanical weathering and chemical weathering. True False ANS:T


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