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Chapter 7: Weathering, Erosion, and Soil

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Presentation on theme: "Chapter 7: Weathering, Erosion, and Soil"— Presentation transcript:

1 Chapter 7: Weathering, Erosion, and Soil

2 relate to weathering and
How does this cartoon relate to weathering and erosion?

3 BIG Idea: Weathering and erosion are agents of change on Earth’s surface.

4 Weathering: the process by which rocks are broken down chemically and physically by the action of water, air, and organisms.

Mechanical Weathering Strictly a physical process Rocks and minerals break into smaller pieces No change to chemical composition

6 Agents of MECHANICAL Weathering:
ice plants and animals gravity running water wind

7 1. Ice (Frost) Wedging water seeps into rock cracks and then freezes

8 What causes this to happen?


10 2. Pressure Exfoliation: outer rock layers are stripped away (like an onion’s layers can be peeled)


12 3. Organic Activity

13 Root Action: tree roots grow within cracks in rocks and cause the rocks to split

14 4. Abrasion The collision of rocks with one another, causing them to break down Agents of abrasion: gravity running water wind

15 wearing down or smoothing
of a material due to constant collisions

16 Wind Abrasion

17 Water Abrasion

18 B. Chemical Weathering Process by which rocks and minerals undergo changes in their composition Can cause some substances to dissolve Some new minerals form New minerals have properties different than those of original rock


20 What items have you seen rusted?
What could you do to such objects to prevent or reduce rusting?

21 Agents of CHEMICAL Weathering:
Water Oxygen Carbon dioxide Acid precipitation

22 Hydrolysis: reacting with water
Carbonation: carbon dioxide combines with water to produce carbonic acid (dissolves limestone) Oxidation: reacting with oxygen (rust)

23 Carbonic acid creates caves

24 Oxidation of the iron in the rock causes a red hue

25 Acid precipitation (rain): sulfur dioxide, carbon dioxide and nitrogen oxides released into atmosphere by human activities; gases combine with oxygen and water to form strong acid rains Plant acids: from decaying plants


27 II. RATES OF WEATHERING All rocks do not weather at the same rate (speed)… Some factors that affect the rate at which rocks weather are:

28 A. Rock Composition Igneous and metamorphic rocks break down more SLOWLY Hardest minerals resist weathering (i.e. quartz) Rocks containing calcite weather QUICKLY

29 Which layer is MORE resistant to weathering? LEAST resistant?



32 B. Amount of Exposure time exposed surface area

33 Surface Area Which will weather faster, solid rock or crushed rock?

34 The crushed rock of course!
the large rock is tightly packed and has less surface area exposed the crushed rock is loosely packed and has more surface area exposed

35 Increased surface area = increased weathering


37 C. Climate Rocks in tropical regions weather faster than rocks in dry desert areas More rain, humidity, wind, and temperature range = faster weathering

38 Physical Weathering: works better in a cool and dry climate Chemical Weathering: works better in a hot and moist environment (more water = more weathering)

39 Cleopatra’s Needle stood in Egypt (hot/dry) for 3,000 years…

40 It was only in New York City for 100 years
Rain, ice, and pollution destroyed it

41 Compare the two tombstones in the next picture…
How do they compare in appearance? Which appears more weathered?

42 marble slate

43 Which tombstone is older?
marble slate

44 This means that rocks can weather at different rates!
marble slate

45 D. Topography Higher elevation = faster weathering (colder, more ice wedging) Steep slopes - gravity pulls rocks down hill

46 III. Weathering and Soil
Soil: loose rock fragments and clay from weathered rock mixed with organic material.

47 A. Soil Composition A = Humus - dark organic material
B & C = Soil – mixture of minerals, gases, and dead organisms D = Regolith – layer of weathered rock fragments E = Bedrock – solid unweathered rock

48 B. Soil Profile Soil Profile: cross section of the soil layers
Horizons: layers in the soil


50 Two Types of Soil: Residual: parent material is the local bedrock
Transported: develops from parent material that has been moved far from original location

51 Residual Soils forms from the weathering of the underlying bedrock

52 Transported Soils Due to…

53 IV. EROSION Process by which the products of weathering are TRANSPORTED (moved) Agents of erosion: Running WATER wind glaciers (ice)

54 A. Gravity and Erosion Talus: rock fragments at the base of a slope

55 Mass Movements Rock fall: fall of rocks from a steep cliff


57 Landslide: loose soil and rocks that move down the slope of a hill



60 Mudflow: rapid movement of a large mass of mud

61 Creep: slow downhill movement of rocks and soil

62 B. Landforms and Erosion
3 major landforms: Mountains: steep, high elevations Plains: flat or gently sloped, not high above sea level Plateaus: high elevations, flat surfaces




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