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Weathering and Soil Formation

Weathering and Soil Formation. Ayers Rock… Another View. Coach Holmes indicator for, “How far out in the boonies are we?” Distance from civilization. Approximately how far away from Ayers Rock is the closest McDonalds restaurant?.

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Weathering and Soil Formation

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  1. Weathering and Soil Formation

  2. Ayers Rock… Another View

  3. Coach Holmes indicator for, “How far out in the boonies are we?” Distance from civilization. Approximately how far away from Ayers Rock is the closest McDonalds restaurant? 465 km (289 miles). The closest McDonalds is in Alice Springs. 22 km to Yulara then another 443 km to Alice Springs

  4. Essential Question: • NCSCOS: EEn.2.1.3 • Explain how natural actions such as weathering, erosion(wind, water and gravity), and soil formation affect the Earth’s surface. • E.Q. - What are the mechanisms of weathering

  5. Objectives and Goals • Recall that soil is the result of weathering of rocks and includes weathered particles: sand, silt and clay. • Explain differences in chemical and physical weathering how weathering rates are affected by a variety of factors including climate, topography and rock composition.

  6. Writing: • In your journals: • Give your definition of weathering.

  7. Part I Weathering • The breaking down of rocks and other materials on the Earth’s surface is called weathering. A slow, continuous process, it affects all substances exposed to the atmosphere.

  8. Types of Weathering • Rocks on the Earth’s surface are broken down by two types of weathering: • mechanical and chemical.

  9. MechanicalWeathering • When the forces of weathering break rocks into smaller pieces but do not change the chemical makeup of the rocks, the process is called mechanical weathering. During mechanical weathering, rocks are broken into different shapes and smaller pieces. At the beginning the edges are jagged, as weathering continues, they become round.

  10. Causes of Mechanical Weathering • Must involve motion or movement • Temperature / Exfoliation • Frost action / Ice wedging • Organic activity / Root Pry • Gravity / Rolling down hill • Abrasion / Sand blasting • Glacier / Till

  11. Temperature • Rocks can be broken apart by changes in temperature. As rocks are heat up in the sun during the day, the outside of the rock expands. The inside of the rocks remain cool and do not expand. When the air temperature drops at night, the outside of the rock cools and contracts. This continuing cycle causes particles to break off. This is called exfoliation.

  12. Rock Exfoliates

  13. Study the figure and answer the questions below in your notebook. a Are the changes in temperature gradual or rapid? b In which regions do these fluctuating temperatures often occur? c Where are the points of weakness in the rock?

  14. Frost Action • Unlike most liquids, water expands when it freezes. The repeated freezing and melting of water, called frost action, is another cause of mechanical weathering. When water freezes in cracks in the rocks, it expands, making the crack larger.In time, this causes the rock to break into pieces.

  15. Ice Wedging / Frost Action

  16. .Study figure and answer the questions below in your notebook • a Where is the rainwater going? • b What happens when temperatures fall below 0°C? • c Why has the crack widened? • d What effect will this have on the rock? • e Which process does this flow chart illustrate?

  17. Organic Activity • Plants and animals can cause mechanical weathering. The roots of plants sometimes loosens rock material. A plant growing in a crack can make the crack larger as the root spread out. This is known as root-pry. It is organic since this activity is caused by living things.

  18. Study the figure and answer the questions below in your notebook. a What happens to the crack as the roots get bigger? b What kind of weathering is this? c What kind of weathering does this process cause? dThe decaying tree will provide…

  19. Gravity • Gravity is another agent of mechanical weathering. Sometimes gravity pulls loosened rocks down mountain cliffs in a landslide. A landslide is a large movement of loose rocks and soil, know as MASS MOVEMENT. As the rocks fall, they collide with one another and break into smaller pieces. Falling rocks usually occur in areas where a road has been cut through, leaving cliffs on both sides.

  20. Abrasion • Wind-blown sand causes mechanical weathering . Abrasion is the wearing away of rocks by solid particles carried by wind, water or other forces. In desert regions or at the beach, the wind easily picks up and moves sand. The sharp edges of the sand particles scrape off pieces of exposed rocks. Running water also carries loose rocks which scrape against each other and break.

  21. Sandblasting Arthttp://www.youtube.com/watch?v=apjYHZKZV6k&safety_mode=true&persist_safety_mode=1

  22. Chemical Weathering • When the chemical makeup of the rocks is changed it is called chemical weathering. During chemical weathering, changes occur in the mineral composition of rocks. Minerals can be added, removed or broken down (decomposed). Many substances react chemically with rocks to break them down.

  23. Types of Chemical Weathering • The chemical composition must be changed • Water /dissolving • Oxidation / Rusting • Carbonation / Acid Rain weak • Sulfuric acid / Acid Rain strong • Plant acids / Mosses and lichens

  24. Water Most chemical weathering is caused by water and carbon dioxide. Water can dissolve most of the mineral that hold rocks together. Rocks that dissolve in water are said to be soluble. Water can form acids when it mixes with certain gases in the atmosphere to speed up the decomposition of rocks. Water can also combine with a mineral to form a new mineral.

  25. Evaporites

  26. Our State (Magazine) • Linville Caverns Video https://www.youtube.com/watch?v=242YYeGdid4

  27. Oxidation • Chemical weathering is also caused by oxidation. Oxidation is the process in which oxygen chemically combines with another substance. The result of oxidation is the formation of an entirely different substance. Iron in rocks combines with oxygen in the air to form iron oxide, or rust.

  28. Carbonation • When carbon dioxide dissolves in water, a weak acid called carbonic acid is formed. When carbonic acid reacts chemically with other substance, the process of carbonation occurs. In nature, carbonic acid is formed when carbon dioxide in the air dissolves in rain. This acid rain falls to the ground and sinks into the soil. It decomposes feldspar and limestone.

  29. Study the figure and answer the questions below in your notebook. a What kind of weathering is this? b How does this kind of weathering affect the rock? c Which climates speed up this kind of weathering?

  30. Sulfuric Acid • The air in certain areas is polluted with sulfur oxides. Sulfur oxides are a byproduct of the burning of coal as a source of energy. These compounds dissolve in rainwater to form sulfuric acid. Rain that contains sulfuric acid is one type of acid rain. It is much stronger than carbonic acid. Sulfuric acid corrodes rocks, metals and other materials quickly.

  31. Plant Acids • Plants produce weak acids that dissolve certain minerals in rocks. Mosses and lichens produce weak acids that dissolve some of the minerals in the rocks they grow on in areas of PERMAFROST / Polar Climates. Gradually the rocks break into smaller pieces. They are important in the formation of soil.

  32. Rate of Weathering • The composition of the rock • The amount of time that the rock is exposed on the Earth’s surface • The amount of exposed surface on a rock • Climate • Relief / Topography (Height)

  33. Rate of Getting Wet Check your understanding of weathering rates. With a partner list five different ways that your clothes become saturated with rain more and/or faster. Then compare that list with your notes on the rates of weathering

  34. Rate of Weathering Graph

  35. Composition of Rocks • Two different types of rocks in the same climate can weather differently, depending on the minerals that make up each rock type. If a rock resist weathering, the rock is called a STABLE ROCK. The stability of a rock can vary depending on the climate in which the rock is found. Limestone is stable in a dry climate but not in a wet climate.

  36. Amount of Time of Exposure • The amount of time that rock is exposed on the Earth’s surface also affects its rate of weathering. A very old rock that has not been exposed to the forces of weathering can remain almost unchanged. If a newly formed rock is deposited on the Earth’s surface it will begin to weather right away.

  37. Which Is Older???? Vs.

  38. The Amount of Exposed Surface • The amount of exposed surface area on a rock also affects its rate of weathering. As rocks are broken down into many small pieces, more rock surfaces are exposed and more weathering takes place. In rocks that contain many joints or cracks, various chemicals easily come into contact with the rock surfaces and break them down.

  39. Which Dome is more exposed??? Vs.

  40. Chimney Tops… G.S.M.N.P.

  41. Climate • Cold and/or dry climates favor physical weathering. Arctic/Polar • Warm and wet climates favor chemical weathering. Tropical • Frost action works best in areas where the temperature fluctuates wildly. Temperate Climates

  42. Part 2

  43. Part II Erosion and Deposition • Essential Question: • Compare erosion by water, wind, ice, and gravity and the effect on various landforms

  44. What Caused This?

  45. What is Erosion? Erosion – the moving of rock material from one place to a new location • For erosion to occur three processes must take place: detachment of particles, lifting them, and transporting them • Many agents of erosion - flowing water, moving ice, waves, gravity, or wind • Sand, silt and clay consists of small pieces of rock that have been weathered from a parent rock, eroded, and deposited somewhere else

  46. What Is Wind Erosion? • Wind- responsible for wearing away rocks and creating great deserts like the Sahara Desert and Gobi • Most effective in moving loose material • Two main effects: (1) Wind causes small particles to be lifted and moved away. (2) Suspended particles may impact on solid objects causing weathering by abrasion (rubbing/blasting). • Occurs in areas where there is not enough rainfall to support vegetation

  47. What Is Water Erosion? • Water - most influential force in erosion • Ability to move materials from one location to another over long distances • The faster water moves in streams the larger objects it can pick up and transport. Known as STREAM LOAD • Responsible for wearing away of rocks in rivers, lakes, and the oceans

  48. What Is Wave Erosion? • Waves - relentless pounding • Erodes the softer, weaker parts of the rock first, leaving harder, more resistant rock behind • Can take over 100 years to erode a rock to sand • Energy of waves along with the chemical content of the water erodes the rock off the coastline

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